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diff --git a/doc/protocol/draft-ietf-tls-rfc4346-bis-03.txt b/doc/protocol/draft-ietf-tls-rfc4346-bis-03.txt deleted file mode 100644 index e41c5b412b..0000000000 --- a/doc/protocol/draft-ietf-tls-rfc4346-bis-03.txt +++ /dev/null @@ -1,5189 +0,0 @@ - - - - - - - Tim Dierks - Independent - Eric Rescorla -INTERNET-DRAFT Network Resonance, Inc. -<draft-ietf-tls-rfc4346-bis-03.txt> March 2007 (Expires September 2007) - - The TLS Protocol - Version 1.2 - -Status of this Memo - By submitting this Internet-Draft, each author represents that any - applicable patent or other IPR claims of which he or she is aware - have been or will be disclosed, and any of which he or she becomes - aware will be disclosed, in accordance with Section 6 of BCP 79. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt. - - The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. - -Copyright Notice - - Copyright (C) The IETF Trust (2007). - -Abstract - - This document specifies Version 1.2 of the Transport Layer Security - (TLS) protocol. The TLS protocol provides communications security - over the Internet. The protocol allows client/server applications to - communicate in a way that is designed to prevent eavesdropping, - tampering, or message forgery. - -Table of Contents - - 1. Introduction 3 - 1.1 Requirements Terminology 4 - 1.2 Major Differences from TLS 1.1 5 - - - -Dierks & Rescorla Standards Track [Page 1] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - 2. Goals 5 - 3. Goals of This Document 6 - 4. Presentation Language 6 - 4.1. Basic Block Size 6 - 4.2. Miscellaneous 7 - 4.3. Vectors 7 - 4.4. Numbers 8 - 4.5. Enumerateds 8 - 4.6. Constructed Types 9 - 4.6.1. Variants 9 - 4.7. Cryptographic Attributes 10 - 4.8. Constants 12 - 5. HMAC and the Pseudorandom fFunction 12 - 6. The TLS Record Protocol 14 - 6.1. Connection States 14 - 6.2. Record layer 17 - 6.2.1. Fragmentation 17 - 6.2.2. Record Compression and Decompression 18 - 6.2.3. Record Payload Protection 19 - 6.2.3.1. Null or Standard Stream Cipher 19 - 6.2.3.2. CBC Block Cipher 20 - 6.2.3.3. AEAD ciphers 22 - 6.3. Key Calculation 23 - 7. The TLS Handshaking Protocols 24 - 7.1. Change Cipher Spec Protocol 25 - 7.2. Alert Protocol 25 - 7.2.1. Closure Alerts 26 - 7.2.2. Error Alerts 27 - 7.3. Handshake Protocol Overview 30 - 7.4. Handshake Protocol 34 - 7.4.1. Hello Messages 35 - 7.4.1.1. Hello Request 35 - 7.4.1.2. Client Hello 36 - 7.4.1.3. Server Hello 39 - 7.4.1.4 Hello Extensions 40 - 7.4.1.4.1 Cert Hash Types 42 - 7.4.2. Server Certificate 42 - 7.4.3. Server Key Exchange Message 44 - 7.4.4. Certificate Request 46 - 7.4.5 Server hello done 47 - 7.4.6. Client Certificate 48 - 7.4.7. Client Key Exchange Message 48 - 7.4.7.1. RSA Encrypted Premaster Secret Message 49 - 7.4.7.1. Client Diffie-Hellman Public Value 51 - 7.4.8. Certificate verify 52 - 7.4.9. Finished 52 - 8. Cryptographic Computations 53 - 8.1. Computing the Master Secret 54 - - - -Dierks & Rescorla Standards Track [Page 2] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - 8.1.1. RSA 54 - 8.1.2. Diffie-Hellman 54 - 9. Mandatory Cipher Suites 54 - A. Protocol Constant Values 58 - A.1. Record Layer 58 - A.2. Change Cipher Specs Message 59 - A.3. Alert Messages 59 - A.4. Handshake Protocol 61 - A.4.1. Hello Messages 61 - A.4.2. Server Authentication and Key Exchange Messages 62 - A.4.3. Client Authentication and Key Exchange Messages 63 - A.4.4. Handshake Finalization Message 64 - A.5. The CipherSuite 64 - A.6. The Security Parameters 67 - B. Glossary 69 - C. CipherSuite Definitions 73 - D. Implementation Notes 75 - D.1 Random Number Generation and Seeding 75 - D.2 Certificates and Authentication 75 - D.3 CipherSuites 75 - E. Backward Compatibility 76 - E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0 76 - E.2 Compatibility with SSL 2.0 77 - E.2. Avoiding Man-in-the-Middle Version Rollback 79 - F. Security Analysis 80 - F.1. Handshake Protocol 80 - F.1.1. Authentication and Key Exchange 80 - F.1.1.1. Anonymous Key Exchange 80 - F.1.1.2. RSA Key Exchange and Authentication 81 - F.1.1.3. Diffie-Hellman Key Exchange with Authentication 81 - F.1.2. Version Rollback Attacks 82 - F.1.3. Detecting Attacks Against the Handshake Protocol 83 - F.1.4. Resuming Sessions 83 - F.1.5 Extensions 83 - F.2. Protecting Application Data 84 - F.3. Explicit IVs 84 - F.4. Security of Composite Cipher Modes 84 - F.5 Denial of Service 85 - F.6. Final Notes 86 - - -1. Introduction - - The primary goal of the TLS Protocol is to provide privacy and data - integrity between two communicating applications. The protocol is - composed of two layers: the TLS Record Protocol and the TLS Handshake - Protocol. At the lowest level, layered on top of some reliable - transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The - - - -Dierks & Rescorla Standards Track [Page 3] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - TLS Record Protocol provides connection security that has two basic - properties: - - - The connection is private. Symmetric cryptography is used for - data encryption (e.g., DES [DES], RC4 [SCH] etc.). The keys for - this symmetric encryption are generated uniquely for each - connection and are based on a secret negotiated by another - protocol (such as the TLS Handshake Protocol). The Record - Protocol can also be used without encryption. - - - The connection is reliable. Message transport includes a message - integrity check using a keyed MAC. Secure hash functions (e.g., - SHA, MD5, etc.) are used for MAC computations. The Record - Protocol can operate without a MAC, but is generally only used in - this mode while another protocol is using the Record Protocol as - a transport for negotiating security parameters. - - The TLS Record Protocol is used for encapsulation of various higher - level protocols. One such encapsulated protocol, the TLS Handshake - Protocol, allows the server and client to authenticate each other and - to negotiate an encryption algorithm and cryptographic keys before - the application protocol transmits or receives its first byte of - data. The TLS Handshake Protocol provides connection security that - has three basic properties: - - - The peer's identity can be authenticated using asymmetric, or - public key, cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This - authentication can be made optional, but is generally required - for at least one of the peers. - - - The negotiation of a shared secret is secure: the negotiated - secret is unavailable to eavesdroppers, and for any authenticated - connection the secret cannot be obtained, even by an attacker who - can place himself in the middle of the connection. - - - The negotiation is reliable: no attacker can modify the - negotiation communication without being detected by the parties - to the communication. - - One advantage of TLS is that it is application protocol independent. - Higher-level protocols can layer on top of the TLS Protocol - transparently. The TLS standard, however, does not specify how - protocols add security with TLS; the decisions on how to initiate TLS - handshaking and how to interpret the authentication certificates - exchanged are left to the judgment of the designers and implementors - of protocols which run on top of TLS. - -1.1 Requirements Terminology - - - -Dierks & Rescorla Standards Track [Page 4] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in RFC 2119 [RFC2119]. - -1.2 Major Differences from TLS 1.1 - This document is a revision of the TLS 1.1 [TLS1.1] protocol which - contains improved flexibility, particularly for negotiation of - cryptographic algorithms. The major changes are: - - - Merged in TLS Extensions definition and AES Cipher Suites from - external documents. - - - Replacement of MD5/SHA-1 combination in the PRF. Addition - of cipher-suite specified PRFs. - - - Replacement of MD5/SHA-1 combination in the digitally-signed - element. - - - Allow the client to indicate which hash functions it supports - for digital signature. - - - Allow the server to indicate which hash functions it supports - for digital signature. - - - Addition of support for authenticated encryption with additional - data modes. - - - Tightened up a number of requirements. - - - The usual clarifications and editorial work. - - -2. Goals - - The goals of TLS Protocol, in order of their priority, are as - follows: - - 1. Cryptographic security: TLS should be used to establish a secure - connection between two parties. - - 2. Interoperability: Independent programmers should be able to - develop applications utilizing TLS that can successfully exchange - cryptographic parameters without knowledge of one another's code. - - 3. Extensibility: TLS seeks to provide a framework into which new - public key and bulk encryption methods can be incorporated as - necessary. This will also accomplish two sub-goals: preventing - the need to create a new protocol (and risking the introduction - - - -Dierks & Rescorla Standards Track [Page 5] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - of possible new weaknesses) and avoiding the need to implement an - entire new security library. - - 4. Relative efficiency: Cryptographic operations tend to be highly - CPU intensive, particularly public key operations. For this - reason, the TLS protocol has incorporated an optional session - caching scheme to reduce the number of connections that need to - be established from scratch. Additionally, care has been taken to - reduce network activity. - -3. Goals of This Document - - This document and the TLS protocol itself are based on the SSL 3.0 - Protocol Specification as published by Netscape. The differences - between this protocol and SSL 3.0 are not dramatic, but they are - significant enough that the various versions of TLS and SSL 3.0 do - not interoperate (although each protocol incorporates a mechanism by - which an implementation can back down to prior versions). This - document is intended primarily for readers who will be implementing - the protocol and for those doing cryptographic analysis of it. The - specification has been written with this in mind, and it is intended - to reflect the needs of those two groups. For that reason, many of - the algorithm-dependent data structures and rules are included in the - body of the text (as opposed to in an appendix), providing easier - access to them. - - This document is not intended to supply any details of service - definition or of interface definition, although it does cover select - areas of policy as they are required for the maintenance of solid - security. - -4. Presentation Language - - This document deals with the formatting of data in an external - representation. The following very basic and somewhat casually - defined presentation syntax will be used. The syntax draws from - several sources in its structure. Although it resembles the - programming language "C" in its syntax and XDR [XDR] in both its - syntax and intent, it would be risky to draw too many parallels. The - purpose of this presentation language is to document TLS only; it has - no have general application beyond that particular goal. - -4.1. Basic Block Size - - The representation of all data items is explicitly specified. The - basic data block size is one byte (i.e., 8 bits). Multiple byte data - items are concatenations of bytes, from left to right, from top to - bottom. From the bytestream, a multi-byte item (a numeric in the - - - -Dierks & Rescorla Standards Track [Page 6] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - example) is formed (using C notation) by: - - value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | - ... | byte[n-1]; - - This byte ordering for multi-byte values is the commonplace network - byte order or big endian format. - -4.2. Miscellaneous - - Comments begin with "/*" and end with "*/". - - Optional components are denoted by enclosing them in "[[ ]]" double - brackets. - - Single-byte entities containing uninterpreted data are of type - opaque. - -4.3. Vectors - - A vector (single dimensioned array) is a stream of homogeneous data - elements. The size of the vector may be specified at documentation - time or left unspecified until runtime. In either case, the length - declares the number of bytes, not the number of elements, in the - vector. The syntax for specifying a new type, T' that is a fixed- - length vector of type T is - - T T'[n]; - - Here, T' occupies n bytes in the data stream, where n is a multiple - of the size of T. The length of the vector is not included in the - encoded stream. - - In the following example, Datum is defined to be three consecutive - bytes that the protocol does not interpret, while Data is three - consecutive Datum, consuming a total of nine bytes. - - opaque Datum[3]; /* three uninterpreted bytes */ - Datum Data[9]; /* 3 consecutive 3 byte vectors */ - - Variable-length vectors are defined by specifying a subrange of legal - lengths, inclusively, using the notation <floor..ceiling>. When - these are encoded, the actual length precedes the vector's contents - in the byte stream. The length will be in the form of a number - consuming as many bytes as required to hold the vector's specified - maximum (ceiling) length. A variable-length vector with an actual - length field of zero is referred to as an empty vector. - - - - -Dierks & Rescorla Standards Track [Page 7] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - T T'<floor..ceiling>; - - In the following example, mandatory is a vector that must contain - between 300 and 400 bytes of type opaque. It can never be empty. The - actual length field consumes two bytes, a uint16, sufficient to - represent the value 400 (see Section 4.4). On the other hand, longer - can represent up to 800 bytes of data, or 400 uint16 elements, and it - may be empty. Its encoding will include a two-byte actual length - field prepended to the vector. The length of an encoded vector must - be an even multiple of the length of a single element (for example, a - 17-byte vector of uint16 would be illegal). - - opaque mandatory<300..400>; - /* length field is 2 bytes, cannot be empty */ - uint16 longer<0..800>; - /* zero to 400 16-bit unsigned integers */ - -4.4. Numbers - - The basic numeric data type is an unsigned byte (uint8). All larger - numeric data types are formed from fixed-length series of bytes - concatenated as described in Section 4.1 and are also unsigned. The - following numeric types are predefined. - - uint8 uint16[2]; - uint8 uint24[3]; - uint8 uint32[4]; - uint8 uint64[8]; - - All values, here and elsewhere in the specification, are stored in - "network" or "big-endian" order; the uint32 represented by the hex - bytes 01 02 03 04 is equivalent to the decimal value 16909060. - - Note that in some cases (e.g., DH parameters) it is necessary to - represent integers as opaque vectors. In such cases, they are - represented as unsigned integers (i.e., leading zero octets are not - required even if the most significant bit is set). - -4.5. Enumerateds - - An additional sparse data type is available called enum. A field of - type enum can only assume the values declared in the definition. - Each definition is a different type. Only enumerateds of the same - type may be assigned or compared. Every element of an enumerated must - be assigned a value, as demonstrated in the following example. Since - the elements of the enumerated are not ordered, they can be assigned - any unique value, in any order. - - - - -Dierks & Rescorla Standards Track [Page 8] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te; - - Enumerateds occupy as much space in the byte stream as would its - maximal defined ordinal value. The following definition would cause - one byte to be used to carry fields of type Color. - - enum { red(3), blue(5), white(7) } Color; - - One may optionally specify a value without its associated tag to - force the width definition without defining a superfluous element. - In the following example, Taste will consume two bytes in the data - stream but can only assume the values 1, 2, or 4. - - enum { sweet(1), sour(2), bitter(4), (32000) } Taste; - - The names of the elements of an enumeration are scoped within the - defined type. In the first example, a fully qualified reference to - the second element of the enumeration would be Color.blue. Such - qualification is not required if the target of the assignment is well - specified. - - Color color = Color.blue; /* overspecified, legal */ - Color color = blue; /* correct, type implicit */ - - For enumerateds that are never converted to external representation, - the numerical information may be omitted. - - enum { low, medium, high } Amount; - -4.6. Constructed Types - - Structure types may be constructed from primitive types for - convenience. Each specification declares a new, unique type. The - syntax for definition is much like that of C. - - struct { - T1 f1; - T2 f2; - ... - Tn fn; - } [[T]]; - - The fields within a structure may be qualified using the type's name, - with a syntax much like that available for enumerateds. For example, - T.f2 refers to the second field of the previous declaration. - Structure definitions may be embedded. - -4.6.1. Variants - - - -Dierks & Rescorla Standards Track [Page 9] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Defined structures may have variants based on some knowledge that is - available within the environment. The selector must be an enumerated - type that defines the possible variants the structure defines. There - must be a case arm for every element of the enumeration declared in - the select. The body of the variant structure may be given a label - for reference. The mechanism by which the variant is selected at - runtime is not prescribed by the presentation language. - - struct { - T1 f1; - T2 f2; - .... - Tn fn; - select (E) { - case e1: Te1; - case e2: Te2; - .... - case en: Ten; - } [[fv]]; - } [[Tv]]; - - For example: - - enum { apple, orange } VariantTag; - struct { - uint16 number; - opaque string<0..10>; /* variable length */ - } V1; - struct { - uint32 number; - opaque string[10]; /* fixed length */ - } V2; - struct { - select (VariantTag) { /* value of selector is implicit */ - case apple: V1; /* VariantBody, tag = apple */ - case orange: V2; /* VariantBody, tag = orange */ - } variant_body; /* optional label on variant */ - } VariantRecord; - - Variant structures may be qualified (narrowed) by specifying a value - for the selector prior to the type. For example, a - - orange VariantRecord - - is a narrowed type of a VariantRecord containing a variant_body of - type V2. - -4.7. Cryptographic Attributes - - - -Dierks & Rescorla Standards Track [Page 10] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - The five cryptographic operations digital signing, stream cipher - encryption, block cipher encryption, authenticated encryption with - additional data (AEAD) encryption and public key encryption are - designated digitally-signed, stream-ciphered, block-ciphered, aead- - ciphered, and public-key-encrypted, respectively. A field's - cryptographic processing is specified by prepending an appropriate - key word designation before the field's type specification. - Cryptographic keys are implied by the current session state (see - Section 6.1). - - In digital signing, one-way hash functions are used as input for a - signing algorithm. A digitally-signed element is encoded as an opaque - vector <0..2^16-1>, where the length is specified by the signing - algorithm and key. - - In RSA signing, the opaque vector contains the signature generated - using the RSASSA-PKCS1-v1_5 signature scheme defined in [PKCS1B]. As - discussed in [PKCS1B], the DigestInfo MUST be DER encoded and for - digest algorithms without parameters (which include SHA-1) the - DigestInfo.AlgorithmIdentifier.parameters field SHOULD be omitted but - implementations MUST accept both without parameters and with NULL - parameters. Note that earlier versions of TLS used a different RSA - signature scheme which did not include a DigestInfo encoding. - - In DSS, the 20 bytes of the SHA-1 hash are run directly through the - Digital Signing Algorithm with no additional hashing. This produces - two values, r and s. The DSS signature is an opaque vector, as above, - the contents of which are the DER encoding of: - - Dss-Sig-Value ::= SEQUENCE { - r INTEGER, - s INTEGER - } - - In stream cipher encryption, the plaintext is exclusive-ORed with an - identical amount of output generated from a cryptographically secure - keyed pseudorandom number generator. - - In block cipher encryption, every block of plaintext encrypts to a - block of ciphertext. All block cipher encryption is done in CBC - (Cipher Block Chaining) mode, and all items that are block-ciphered - will be an exact multiple of the cipher block length. - - In AEAD encryption, the plaintext is simultaneously encrypted and - integrity protected. The input may be of any length and the output is - generally larger than the input in order to accomodate the integrity - check value. - - - - -Dierks & Rescorla Standards Track [Page 11] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - In public key encryption, a public key algorithm is used to encrypt - data in such a way that it can be decrypted only with the matching - private key. A public-key-encrypted element is encoded as an opaque - vector <0..2^16-1>, where the length is specified by the signing - algorithm and key. - - RSA encryption is done using the RSAES-PKCS1-v1_5 encryption scheme - defined in [PKCS1B]. - - In the following example - - stream-ciphered struct { - uint8 field1; - uint8 field2; - digitally-signed opaque hash[20]; - } UserType; - - the contents of hash are used as input for the signing algorithm, and - then the entire structure is encrypted with a stream cipher. The - length of this structure, in bytes would be equal to two bytes for - field1 and field2, plus two bytes for the length of the signature, - plus the length of the output of the signing algorithm. This is known - because the algorithm and key used for the signing are known prior to - encoding or decoding this structure. - -4.8. Constants - - Typed constants can be defined for purposes of specification by - declaring a symbol of the desired type and assigning values to it. - Under-specified types (opaque, variable length vectors, and - structures that contain opaque) cannot be assigned values. No fields - of a multi-element structure or vector may be elided. - - For example: - - struct { - uint8 f1; - uint8 f2; - } Example1; - - Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */ - -5. HMAC and the Pseudorandom fFunction - - A number of operations in the TLS record and handshake layer requires - a keyed MAC; this is a secure digest of some data protected by a - secret. Forging the MAC is infeasible without knowledge of the MAC - secret. The construction TLS provides for this operation is known as - - - -Dierks & Rescorla Standards Track [Page 12] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - HMAC and is described in [HMAC]. Cipher suites MAY define their own - MACs. - - In addition, a construction is required to do expansion of secrets - into blocks of data for the purposes of key generation or validation. - This pseudo-random function (PRF) takes as input a secret, a seed, - and an identifying label and produces an output of arbitrary length. - We define one PRF, based on HMAC, which is used for all cipher suites - in this document. Cipher suites MAY define their own PRFs. - - First, we define a data expansion function, P_hash(secret, data) that - uses a single hash function to expand a secret and seed into an - arbitrary quantity of output: - - P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) + - HMAC_hash(secret, A(2) + seed) + - HMAC_hash(secret, A(3) + seed) + ... - - Where + indicates concatenation. - - A() is defined as: - A(0) = seed - A(i) = HMAC_hash(secret, A(i-1)) - - P_hash can be iterated as many times as is necessary to produce the - required quantity of data. For example, if P_SHA-1 is being used to - create 64 bytes of data, it will have to be iterated 4 times (through - A(4)), creating 80 bytes of output data; the last 16 bytes of the - final iteration will then be discarded, leaving 64 bytes of output - data. - - TLS's PRF is created by applying P_hash to the secret S as: - - PRF(secret, label, seed) = P_<hash>(secret, label + seed) - - All the cipher suites defined in this document and in TLS documents - prior to this document MUST use SHA-256 as the basis for their PRF. - New cipher suites MUST specify a PRF and in general SHOULD use the - TLS PRF with SHA-256 or a stronger standard hash function. - - The label is an ASCII string. It should be included in the exact form - it is given without a length byte or trailing null character. For - example, the label "slithy toves" would be processed by hashing the - following bytes: - - 73 6C 69 74 68 79 20 74 6F 76 65 73 - - - - - -Dierks & Rescorla Standards Track [Page 13] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -6. The TLS Record Protocol - - The TLS Record Protocol is a layered protocol. At each layer, - messages may include fields for length, description, and content. - The Record Protocol takes messages to be transmitted, fragments the - data into manageable blocks, optionally compresses the data, applies - a MAC, encrypts, and transmits the result. Received data is - decrypted, verified, decompressed, and reassembled, and then - delivered to higher-level clients. - - Four record protocol clients are described in this document: the - handshake protocol, the alert protocol, the change cipher spec - protocol, and the application data protocol. In order to allow - extension of the TLS protocol, additional record types can be - supported by the record protocol. New record type values are assigned - by IANA as described in Section 11. - - - If a TLS implementation receives a record type it does not - understand, it SHOULD just ignore it. Any protocol designed for use - over TLS MUST be carefully designed to deal with all possible attacks - against it. Note that because the type and length of a record are - not protected by encryption, care SHOULD be taken to minimize the - value of traffic analysis of these values. Implementations MUST not - send record types not defined in this document unless negotiated by - some extension. - -6.1. Connection States - - A TLS connection state is the operating environment of the TLS Record - Protocol. It specifies a compression algorithm, encryption algorithm, - and MAC algorithm. In addition, the parameters for these algorithms - are known: the MAC secret and the bulk encryption keys for the - connection in both the read and the write directions. Logically, - there are always four connection states outstanding: the current read - and write states, and the pending read and write states. All records - are processed under the current read and write states. The security - parameters for the pending states can be set by the TLS Handshake - Protocol, and the Change Cipher Spec can selectively make either of - the pending states current, in which case the appropriate current - state is disposed of and replaced with the pending state; the pending - state is then reinitialized to an empty state. It is illegal to make - a state that has not been initialized with security parameters a - current state. The initial current state always specifies that no - encryption, compression, or MAC will be used. - - The security parameters for a TLS Connection read and write state are - set by providing the following values: - - - -Dierks & Rescorla Standards Track [Page 14] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - connection end - Whether this entity is considered the "client" or the "server" in - this connection. - - bulk encryption algorithm - An algorithm to be used for bulk encryption. This specification - includes the key size of this algorithm, how much of that key is - secret, whether it is a block, stream, or AEAD cipher, and the - block size of the cipher (if appropriate). - - MAC algorithm - An algorithm to be used for message authentication. This - specification includes the size of the hash that is returned by - the MAC algorithm. - - compression algorithm - An algorithm to be used for data compression. This specification - must include all information the algorithm requires to do - compression. - - master secret - A 48-byte secret shared between the two peers in the connection. - - client random - A 32-byte value provided by the client. - - server random - A 32-byte value provided by the server. - - These parameters are defined in the presentation language as: - - enum { server, client } ConnectionEnd; - - enum { null, rc4, rc2, des, 3des, des40, idea, aes } BulkCipherAlgorithm; - - enum { stream, block, aead } CipherType; - - enum { null, md5, sha, sha256, sha384, sha512} MACAlgorithm; - - /* The use of "sha" above is historical and denotes SHA-1 */ - - enum { null(0), (255) } CompressionMethod; - - /* The algorithms specified in CompressionMethod, - BulkCipherAlgorithm, and MACAlgorithm may be added to. */ - - struct { - ConnectionEnd entity; - - - -Dierks & Rescorla Standards Track [Page 15] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - BulkCipherAlgorithm bulk_cipher_algorithm; - CipherType cipher_type; - uint8 enc_key_length; - uint8 block_length; - uint8 iv_length; - MACAlgorithm mac_algorithm; - uint8 mac_length; - uint8 mac_key_length; - CompressionMethod compression_algorithm; - opaque master_secret[48]; - opaque client_random[32]; - opaque server_random[32]; - } SecurityParameters; - - The record layer will use the security parameters to generate the - following four items: - - client write MAC secret - server write MAC secret - client write key - server write key - - The client write parameters are used by the server when receiving and - processing records and vice-versa. The algorithm used for generating - these items from the security parameters is described in Section 6.3. - - Once the security parameters have been set and the keys have been - generated, the connection states can be instantiated by making them - the current states. These current states MUST be updated for each - record processed. Each connection state includes the following - elements: - - compression state - The current state of the compression algorithm. - - cipher state - The current state of the encryption algorithm. This will consist - of the scheduled key for that connection. For stream ciphers, - this will also contain whatever state information is necessary to - allow the stream to continue to encrypt or decrypt data. - - MAC secret - The MAC secret for this connection, as generated above. - - sequence number - Each connection state contains a sequence number, which is - maintained separately for read and write states. The sequence - number MUST be set to zero whenever a connection state is made - - - -Dierks & Rescorla Standards Track [Page 16] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - the active state. Sequence numbers are of type uint64 and may not - exceed 2^64-1. Sequence numbers do not wrap. If a TLS - implementation would need to wrap a sequence number, it must - renegotiate instead. A sequence number is incremented after each - record: specifically, the first record transmitted under a - particular connection state MUST use sequence number 0. - -6.2. Record layer - - The TLS Record Layer receives uninterpreted data from higher layers - in non-empty blocks of arbitrary size. - -6.2.1. Fragmentation - - The record layer fragments information blocks into TLSPlaintext - records carrying data in chunks of 2^14 bytes or less. Client message - boundaries are not preserved in the record layer (i.e., multiple - client messages of the same ContentType MAY be coalesced into a - single TLSPlaintext record, or a single message MAY be fragmented - across several records). - - - struct { - uint8 major, minor; - } ProtocolVersion; - - enum { - change_cipher_spec(20), alert(21), handshake(22), - application_data(23), (255) - } ContentType; - - struct { - ContentType type; - ProtocolVersion version; - uint16 length; - opaque fragment[TLSPlaintext.length]; - } TLSPlaintext; - - type - The higher-level protocol used to process the enclosed fragment. - - version - The version of the protocol being employed. This document - describes TLS Version 1.2, which uses the version { 3, 3 }. The - version value 3.3 is historical, deriving from the use of 3.1 for - TLS 1.0. (See Appendix A.1). Note that a client that supports - multiple versions of TLS may not know what version will be - employed before it receives ServerHello. See Appendix E for - - - -Dierks & Rescorla Standards Track [Page 17] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - discussion about what record layer version number should be - employed for ClientHello. - - length - The length (in bytes) of the following TLSPlaintext.fragment. - The length MUST not exceed 2^14. - - fragment - The application data. This data is transparent and treated as an - independent block to be dealt with by the higher-level protocol - specified by the type field. - - Implementations MUST not send zero-length fragments of Handshake, - Alert, or Change Cipher Spec content types. Zero-length fragments - of Application data MAY be sent as they are potentially useful as - a traffic analysis countermeasure. - - Note: Data of different TLS Record layer content types MAY be - interleaved. Application data is generally of lower precedence - for transmission than other content types. However, records MUST - be delivered to the network in the same order as they are - protected by the record layer. Recipients MUST receive and - process interleaved application layer traffic during handshakes - subsequent to the first one on a connection. - - -6.2.2. Record Compression and Decompression - - All records are compressed using the compression algorithm defined in - the current session state. There is always an active compression - algorithm; however, initially it is defined as - CompressionMethod.null. The compression algorithm translates a - TLSPlaintext structure into a TLSCompressed structure. Compression - functions are initialized with default state information whenever a - connection state is made active. - - Compression must be lossless and may not increase the content length - by more than 1024 bytes. If the decompression function encounters a - TLSCompressed.fragment that would decompress to a length in excess of - 2^14 bytes, it MUST report a fatal decompression failure error. - - struct { - ContentType type; /* same as TLSPlaintext.type */ - ProtocolVersion version;/* same as TLSPlaintext.version */ - uint16 length; - opaque fragment[TLSCompressed.length]; - } TLSCompressed; - - - - -Dierks & Rescorla Standards Track [Page 18] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - length - The length (in bytes) of the following TLSCompressed.fragment. - The length should not exceed 2^14 + 1024. - - fragment - The compressed form of TLSPlaintext.fragment. - - Note: A CompressionMethod.null operation is an identity operation; no - fields are altered. - - Implementation note: - Decompression functions are responsible for ensuring that - messages cannot cause internal buffer overflows. - -6.2.3. Record Payload Protection - - The encryption and MAC functions translate a TLSCompressed structure - into a TLSCiphertext. The decryption functions reverse the process. - The MAC of the record also includes a sequence number so that - missing, extra, or repeated messages are detectable. - - struct { - ContentType type; - ProtocolVersion version; - uint16 length; - select (SecurityParameters.cipher_type) { - case stream: GenericStreamCipher; - case block: GenericBlockCipher; - case aead: GenericAEADCipher; - } fragment; - } TLSCiphertext; - - type - The type field is identical to TLSCompressed.type. - - version - The version field is identical to TLSCompressed.version. - - length - The length (in bytes) of the following TLSCiphertext.fragment. - The length may not exceed 2^14 + 2048. - - fragment - The encrypted form of TLSCompressed.fragment, with the MAC. - -6.2.3.1. Null or Standard Stream Cipher - - Stream ciphers (including BulkCipherAlgorithm.null, see Appendix A.6) - - - -Dierks & Rescorla Standards Track [Page 19] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - convert TLSCompressed.fragment structures to and from stream - TLSCiphertext.fragment structures. - - stream-ciphered struct { - opaque content[TLSCompressed.length]; - opaque MAC[SecurityParameters.mac_length]; - } GenericStreamCipher; - - The MAC is generated as: - - HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type + - TLSCompressed.version + TLSCompressed.length + - TLSCompressed.fragment)); - - where "+" denotes concatenation. - - seq_num - The sequence number for this record. - - hash - The hashing algorithm specified by - SecurityParameters.mac_algorithm. - - Note that the MAC is computed before encryption. The stream cipher - encrypts the entire block, including the MAC. For stream ciphers that - do not use a synchronization vector (such as RC4), the stream cipher - state from the end of one record is simply used on the subsequent - packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL, encryption - consists of the identity operation (i.e., the data is not encrypted, - and the MAC size is zero, implying that no MAC is used). - TLSCiphertext.length is TLSCompressed.length plus - SecurityParameters.mac_length. - -6.2.3.2. CBC Block Cipher - - For block ciphers (such as RC2, DES, or AES), the encryption and MAC - functions convert TLSCompressed.fragment structures to and from block - TLSCiphertext.fragment structures. - - block-ciphered struct { - opaque IV[SecurityParameters.block_length]; - opaque content[TLSCompressed.length]; - opaque MAC[SecurityParameters.mac_length]; - uint8 padding[GenericBlockCipher.padding_length]; - uint8 padding_length; - } GenericBlockCipher; - - The MAC is generated as described in Section 6.2.3.1. - - - -Dierks & Rescorla Standards Track [Page 20] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - IV - TLS 1.2 uses an explicit IV in order to prevent the attacks - described by [CBCATT]. The IV SHOULD be chosen at random and MUST - be unpredictable. In order to decrypt, thereceiver decrypts the - entire GenericBlockCipher structure and then discards the first - cipher block, corresponding to the IV component. - - padding - Padding that is added to force the length of the plaintext to be - an integral multiple of the block cipher's block length. The - padding MAY be any length up to 255 bytes, as long as it results - in the TLSCiphertext.length being an integral multiple of the - block length. Lengths longer than necessary might be desirable to - frustrate attacks on a protocol based on analysis of the lengths - of exchanged messages. Each uint8 in the padding data vector MUST - be filled with the padding length value. The receiver MUST check - this padding and SHOULD use the bad_record_mac alert to indicate - padding errors. - - padding_length - The padding length MUST be such that the total size of the - GenericBlockCipher structure is a multiple of the cipher's block - length. Legal values range from zero to 255, inclusive. This - length specifies the length of the padding field exclusive of the - padding_length field itself. - - The encrypted data length (TLSCiphertext.length) is one more than the - sum of TLSCompressed.length, SecurityParameters.mac_length, and - padding_length. - - Example: If the block length is 8 bytes, the content length - (TLSCompressed.length) is 61 bytes, and the MAC length is 20 - bytes, then the length before padding is 82 bytes (this does - not include the IV, which may or may not be encrypted, as - discussed above). Thus, the padding length modulo 8 must be - equal to 6 in order to make the total length an even multiple - of 8 bytes (the block length). The padding length can be 6, - 14, 22, and so on, through 254. If the padding length were the - minimum necessary, 6, the padding would be 6 bytes, each - containing the value 6. Thus, the last 8 octets of the - GenericBlockCipher before block encryption would be xx 06 06 - 06 06 06 06 06, where xx is the last octet of the MAC. - - Note: With block ciphers in CBC mode (Cipher Block Chaining), - it is critical that the entire plaintext of the record be known - before any ciphertext is transmitted. Otherwise, it is possible - for the attacker to mount the attack described in [CBCATT]. - - - - -Dierks & Rescorla Standards Track [Page 21] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Implementation Note: Canvel et al. [CBCTIME] have demonstrated a timing - attack on CBC padding based on the time required to compute the - MAC. In order to defend against this attack, implementations MUST - ensure that record processing time is essentially the same - whether or not the padding is correct. In general, the best way - to do this is to compute the MAC even if the padding is - incorrect, and only then reject the packet. For instance, if the - pad appears to be incorrect, the implementation might assume a - zero-length pad and then compute the MAC. This leaves a small - timing channel, since MAC performance depends to some extent on - the size of the data fragment, but it is not believed to be large - enough to be exploitable, due to the large block size of existing - MACs and the small size of the timing signal. - -6.2.3.3. AEAD ciphers - - For AEAD [AEAD] ciphers (such as [CCM] or [GCM]) the AEAD function - converts TLSCompressed.fragment structures to and from AEAD - TLSCiphertext.fragment structures. - - aead-ciphered struct { - opaque IV[SecurityParameters.iv_length]; - opaque aead_output[AEADEncrypted.length]; - } GenericAEADCipher; - - AEAD ciphers take as input a single key, a nonce, a plaintext, and - "additional data" to be included in the authentication check, as - described in Section 2.1 of [AEAD]. These inputs are as follows. - - The key is either the client_write_key or the server_write_key. The - MAC key will be of length zero. - - The nonce supplied to the AEAD operations is determined by the IV in - aead-ciphered struct. Each IV used in distinct invocations of the - AEAD encryption operation MUST be distinct, for any fixed value of - the key. Implementations SHOULD use the recommended nonce formation - method of [AEAD] to generate IVs, and MAY use any other method that - meets this requirement. The length of the IV depends on the AEAD - cipher; that length MAY be zero. Note that in many cases it is - appropriate to use the partially implicit nonce technique of S 3.2.1 - of AEAD, in which case the client_write_iv and server_write_iv should - be used as the "fixed-common". - - The plaintext is the TLSCompressed.fragment. - - The additional authenticated data, which we denote as - additional_data, is defined as follows: - - - - -Dierks & Rescorla Standards Track [Page 22] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - additional_data = seq_num + TLSCompressed.type + - TLSCompressed.version + TLSCompressed.length; - - The aead_output consists of the ciphertext output by the AEAD - encryption operation. AEADEncrypted.length will generally be larger - than TLSCompressed.length, but by an amount that varies with the AEAD - cipher. Since the ciphers might incorporate padding, the amount of - overhead could vary with different TLSCompressed.length values. Each - AEAD cipher MUST NOT produce an expansion of greater than 1024 bytes. - Symbolically, - - AEADEncrypted = AEAD-Encrypt(key, IV, plaintext, - additional_data) - - Where "+" denotes concatenation. - - - In order to decrypt and verify, the cipher takes as input the key, - IV, the "additional_data", and the AEADEncrypted value. The output is - either the plaintext or an error indicating that the decryption - failed. There is no separate integrity check. I.e., - - TLSCompressed.fragment = AEAD-Decrypt(write_key, IV, AEADEncrypted, - TLSCiphertext.type + TLSCiphertext.version + - TLSCiphertext.length); - - If the decryption fails, a fatal bad_record_mac alert MUST be - generated. - -6.3. Key Calculation - - The Record Protocol requires an algorithm to generate keys, and MAC - secrets from the security parameters provided by the handshake - protocol. - - The master secret is hashed into a sequence of secure bytes, which - are assigned to the MAC secrets and keys required by the current - connection state (see Appendix A.6). CipherSpecs require a client - write MAC secret, a server write MAC secret, a client write key, and - a server write key, each of which is generated from the master secret - in that order. Unused values are empty. - - When keys and MAC secrets are generated, the master secret is used as - an entropy source. - - To generate the key material, compute - - key_block = PRF(SecurityParameters.master_secret, - - - -Dierks & Rescorla Standards Track [Page 23] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - "key expansion", - SecurityParameters.server_random + - SecurityParameters.client_random); - - until enough output has been generated. Then the key_block is - partitioned as follows: - - client_write_MAC_secret[SecurityParameters.mac_key_length] - server_write_MAC_secret[SecurityParameters.mac_key_length] - client_write_key[SecurityParameters.enc_key_length] - server_write_key[SecurityParameters.enc_key_length] - - - Implementation note: - The currently defined cipher suite which requires the most - material is AES_256_CBC_SHA, defined in [TLSAES]. It requires 2 x - 32 byte keys and 2 x 20 byte MAC secrets, for a total 104 bytes - of key material. - -7. The TLS Handshaking Protocols - - TLS has three subprotocols that are used to allow peers to agree - upon security parameters for the record layer, to authenticate - themselves, to instantiate negotiated security parameters, and to - report error conditions to each other. - - The Handshake Protocol is responsible for negotiating a session, - which consists of the following items: - - session identifier - An arbitrary byte sequence chosen by the server to identify an - active or resumable session state. - - peer certificate - X509v3 [X509] certificate of the peer. This element of the - state may be null. - - compression method - The algorithm used to compress data prior to encryption. - - cipher spec - Specifies the bulk data encryption algorithm (such as null, - DES, etc.) and a MAC algorithm (such as MD5 or SHA). It also - defines cryptographic attributes such as the hash_size. (See - Appendix A.6 for formal definition,) - - master secret - 48-byte secret shared between the client and server. - - - -Dierks & Rescorla Standards Track [Page 24] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - is resumable - A flag indicating whether the session can be used to initiate - new connections. - - These items are then used to create security parameters for use by - the Record Layer when protecting application data. Many connections - can be instantiated using the same session through the resumption - feature of the TLS Handshake Protocol. - -7.1. Change Cipher Spec Protocol - - The change cipher spec protocol exists to signal transitions in - ciphering strategies. The protocol consists of a single message, - which is encrypted and compressed under the current (not the pending) - connection state. The message consists of a single byte of value 1. - - struct { - enum { change_cipher_spec(1), (255) } type; - } ChangeCipherSpec; - - The change cipher spec message is sent by both the client and the - server to notify the receiving party that subsequent records will be - protected under the newly negotiated CipherSpec and keys. Reception - of this message causes the receiver to instruct the Record Layer to - immediately copy the read pending state into the read current state. - Immediately after sending this message, the sender MUST instruct the - record layer to make the write pending state the write active state. - (See Section 6.1.) The change cipher spec message is sent during the - handshake after the security parameters have been agreed upon, but - before the verifying finished message is sent (see Section 7.4.11 - - Note: If a rehandshake occurs while data is flowing on a connection, - the communicating parties may continue to send data using the old - CipherSpec. However, once the ChangeCipherSpec has been sent, the new - CipherSpec MUST be used. The first side to send the ChangeCipherSpec - does not know that the other side has finished computing the new - keying material (e.g., if it has to perform a time consuming public - key operation). Thus, a small window of time, during which the - recipient must buffer the data, MAY exist. In practice, with modern - machines this interval is likely to be fairly short. - -7.2. Alert Protocol - - One of the content types supported by the TLS Record layer is the - alert type. Alert messages convey the severity of the message and a - description of the alert. Alert messages with a level of fatal result - in the immediate termination of the connection. In this case, other - connections corresponding to the session may continue, but the - - - -Dierks & Rescorla Standards Track [Page 25] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - session identifier MUST be invalidated, preventing the failed session - from being used to establish new connections. Like other messages, - alert messages are encrypted and compressed, as specified by the - current connection state. - - enum { warning(1), fatal(2), (255) } AlertLevel; - - enum { - close_notify(0), - unexpected_message(10), - bad_record_mac(20), - decryption_failed_RESERVED(21), - record_overflow(22), - decompression_failure(30), - handshake_failure(40), - no_certificate_RESERVED(41), - bad_certificate(42), - unsupported_certificate(43), - certificate_revoked(44), - certificate_expired(45), - certificate_unknown(46), - illegal_parameter(47), - unknown_ca(48), - access_denied(49), - decode_error(50), - decrypt_error(51), - export_restriction_RESERVED(60), - protocol_version(70), - insufficient_security(71), - internal_error(80), - user_canceled(90), - no_renegotiation(100), - unsupported_extension(110), /* new */ - (255) - } AlertDescription; - - struct { - AlertLevel level; - AlertDescription description; - } Alert; - -7.2.1. Closure Alerts - - The client and the server must share knowledge that the connection is - ending in order to avoid a truncation attack. Either party may - initiate the exchange of closing messages. - - close_notify - - - -Dierks & Rescorla Standards Track [Page 26] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - This message notifies the recipient that the sender will not send - any more messages on this connection. Note that as of TLS 1.1, - failure to properly close a connection no longer requires that a - session not be resumed. This is a change from TLS 1.0 to conform - with widespread implementation practice. - - Either party may initiate a close by sending a close_notify alert. - Any data received after a closure alert is ignored. - - Unless some other fatal alert has been transmitted, each party is - required to send a close_notify alert before closing the write side - of the connection. The other party MUST respond with a close_notify - alert of its own and close down the connection immediately, - discarding any pending writes. It is not required for the initiator - of the close to wait for the responding close_notify alert before - closing the read side of the connection. - - If the application protocol using TLS provides that any data may be - carried over the underlying transport after the TLS connection is - closed, the TLS implementation must receive the responding - close_notify alert before indicating to the application layer that - the TLS connection has ended. If the application protocol will not - transfer any additional data, but will only close the underlying - transport connection, then the implementation MAY choose to close the - transport without waiting for the responding close_notify. No part of - this standard should be taken to dictate the manner in which a usage - profile for TLS manages its data transport, including when - connections are opened or closed. - - Note: It is assumed that closing a connection reliably delivers - pending data before destroying the transport. - -7.2.2. Error Alerts - - Error handling in the TLS Handshake protocol is very simple. When an - error is detected, the detecting party sends a message to the other - party. Upon transmission or receipt of a fatal alert message, both - parties immediately close the connection. Servers and clients MUST - forget any session-identifiers, keys, and secrets associated with a - failed connection. Thus, any connection terminated with a fatal alert - MUST NOT be resumed. The following error alerts are defined: - - unexpected_message - An inappropriate message was received. This alert is always fatal - and should never be observed in communication between proper - implementations. - - bad_record_mac - - - -Dierks & Rescorla Standards Track [Page 27] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - This alert is returned if a record is received with an incorrect - MAC. This alert also MUST be returned if an alert is sent because - a TLSCiphertext decrypted in an invalid way: either it wasn't an - even multiple of the block length, or its padding values, when - checked, weren't correct. This message is always fatal. - - decryption_failed_RESERVED - This alert was used in some earlier versions of TLS, and may have - permitted certain attacks against the CBC mode [CBCATT]. It MUST - NOT be sent by compliant implementations. - - record_overflow - A TLSCiphertext record was received that had a length more than - 2^14+2048 bytes, or a record decrypted to a TLSCompressed record - with more than 2^14+1024 bytes. This message is always fatal. - - decompression_failure - The decompression function received improper input (e.g., data - that would expand to excessive length). This message is always - fatal. - - handshake_failure - Reception of a handshake_failure alert message indicates that the - sender was unable to negotiate an acceptable set of security - parameters given the options available. This is a fatal error. - - no_certificate_RESERVED - This alert was used in SSLv3 but not any version of TLS. It MUST - NOT be sent by compliant implementations. - - bad_certificate - A certificate was corrupt, contained signatures that did not - verify correctly, etc. - - unsupported_certificate - A certificate was of an unsupported type. - - certificate_revoked - A certificate was revoked by its signer. - - certificate_expired - A certificate has expired or is not currently valid. - - certificate_unknown - Some other (unspecified) issue arose in processing the - certificate, rendering it unacceptable. - - illegal_parameter - - - -Dierks & Rescorla Standards Track [Page 28] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - A field in the handshake was out of range or inconsistent with - other fields. This is always fatal. - - unknown_ca - A valid certificate chain or partial chain was received, but the - certificate was not accepted because the CA certificate could not - be located or couldn't be matched with a known, trusted CA. This - message is always fatal. - - access_denied - A valid certificate was received, but when access control was - applied, the sender decided not to proceed with negotiation. - This message is always fatal. - - decode_error - A message could not be decoded because some field was out of the - specified range or the length of the message was incorrect. This - message is always fatal. - - decrypt_error - A handshake cryptographic operation failed, including being - unable to correctly verify a signature, decrypt a key exchange, - or validate a finished message. - - export_restriction_RESERVED - This alert was used in some earlier versions of TLS. It MUST NOT - be sent by compliant implementations. - - protocol_version - The protocol version the client has attempted to negotiate is - recognized but not supported. (For example, old protocol versions - might be avoided for security reasons). This message is always - fatal. - - insufficient_security - Returned instead of handshake_failure when a negotiation has - failed specifically because the server requires ciphers more - secure than those supported by the client. This message is always - fatal. - - internal_error - An internal error unrelated to the peer or the correctness of the - protocol (such as a memory allocation failure) makes it - impossible to continue. This message is always fatal. - - user_canceled - This handshake is being canceled for some reason unrelated to a - protocol failure. If the user cancels an operation after the - - - -Dierks & Rescorla Standards Track [Page 29] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - handshake is complete, just closing the connection by sending a - close_notify is more appropriate. This alert should be followed - by a close_notify. This message is generally a warning. - - no_renegotiation - Sent by the client in response to a hello request or by the - server in response to a client hello after initial handshaking. - Either of these would normally lead to renegotiation; when that - is not appropriate, the recipient should respond with this alert. - At that point, the original requester can decide whether to - proceed with the connection. One case where this would be - appropriate is where a server has spawned a process to satisfy a - request; the process might receive security parameters (key - length, authentication, etc.) at startup and it might be - difficult to communicate changes to these parameters after that - point. This message is always a warning. - - unsupported_extension - sent by clients that receive an extended server hello containing - an extension that they did not put in the corresponding client - hello (see Section 2.3). This message is always fatal. - - For all errors where an alert level is not explicitly specified, the - sending party MAY determine at its discretion whether this is a fatal - error or not; if an alert with a level of warning is received, the - receiving party MAY decide at its discretion whether to treat this as - a fatal error or not. However, all messages which are transmitted - with a level of fatal MUST be treated as fatal messages. - - New Alert values are assigned by IANA as described in Section 11. - -7.3. Handshake Protocol Overview - - The cryptographic parameters of the session state are produced by the - TLS Handshake Protocol, which operates on top of the TLS Record - Layer. When a TLS client and server first start communicating, they - agree on a protocol version, select cryptographic algorithms, - optionally authenticate each other, and use public-key encryption - techniques to generate shared secrets. - - The TLS Handshake Protocol involves the following steps: - - - Exchange hello messages to agree on algorithms, exchange random - values, and check for session resumption. - - - Exchange the necessary cryptographic parameters to allow the - client and server to agree on a premaster secret. - - - - -Dierks & Rescorla Standards Track [Page 30] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - - Exchange certificates and cryptographic information to allow the - client and server to authenticate themselves. - - - Generate a master secret from the premaster secret and exchanged - random values. - - - Provide security parameters to the record layer. - - - Allow the client and server to verify that their peer has - calculated the same security parameters and that the handshake - occurred without tampering by an attacker. - - Note that higher layers should not be overly reliant on whether TLS - always negotiates the strongest possible connection between two - peers. There are a number of ways in which a man in the middle - attacker can attempt to make two entities drop down to the least - secure method they support. The protocol has been designed to - minimize this risk, but there are still attacks available: for - example, an attacker could block access to the port a secure service - runs on, or attempt to get the peers to negotiate an unauthenticated - connection. The fundamental rule is that higher levels must be - cognizant of what their security requirements are and never transmit - information over a channel less secure than what they require. The - TLS protocol is secure in that any cipher suite offers its promised - level of security: if you negotiate 3DES with a 1024 bit RSA key - exchange with a host whose certificate you have verified, you can - expect to be that secure. - - These goals are achieved by the handshake protocol, which can be - summarized as follows: The client sends a client hello message to - which the server must respond with a server hello message, or else a - fatal error will occur and the connection will fail. The client hello - and server hello are used to establish security enhancement - capabilities between client and server. The client hello and server - hello establish the following attributes: Protocol Version, Session - ID, Cipher Suite, and Compression Method. Additionally, two random - values are generated and exchanged: ClientHello.random and - ServerHello.random. - - The actual key exchange uses up to four messages: the server - certificate, the server key exchange, the client certificate, and the - client key exchange. New key exchange methods can be created by - specifying a format for these messages and by defining the use of the - messages to allow the client and server to agree upon a shared - secret. This secret MUST be quite long; currently defined key - exchange methods exchange secrets that range from 48 to 128 bytes in - length. - - - - -Dierks & Rescorla Standards Track [Page 31] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Following the hello messages, the server will send its certificate, - if it is to be authenticated. Additionally, a server key exchange - message may be sent, if it is required (e.g., if their server has no - certificate, or if its certificate is for signing only). If the - server is authenticated, it may request a certificate from the - client, if that is appropriate to the cipher suite selected. Next, - the server will send the server hello done message, indicating that - the hello-message phase of the handshake is complete. The server will - then wait for a client response. If the server has sent a certificate - request message, the client must send the certificate message. The - client key exchange message is now sent, and the content of that - message will depend on the public key algorithm selected between the - client hello and the server hello. If the client has sent a - certificate with signing ability, a digitally-signed certificate - verify message is sent to explicitly verify possession of the private - key in the certificate. - - At this point, a change cipher spec message is sent by the client, - and the client copies the pending Cipher Spec into the current Cipher - Spec. The client then immediately sends the finished message under - the new algorithms, keys, and secrets. In response, the server will - send its own change cipher spec message, transfer the pending to the - current Cipher Spec, and send its finished message under the new - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 32] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Cipher Spec. At this point, the handshake is complete, and the client - and server may begin to exchange application layer data. (See flow - chart below.) Application data MUST NOT be sent prior to the - completion of the first handshake (before a cipher suite other - TLS_NULL_WITH_NULL_NULL is established). - - Client Server - - ClientHello --------> - ServerHello - Certificate* - CertificateStatus* - ServerKeyExchange* - CertificateRequest* - <-------- ServerHelloDone - Certificate* - CertificateURL* - ClientKeyExchange - CertificateVerify* - [ChangeCipherSpec] - Finished --------> - [ChangeCipherSpec] - <-------- Finished - Application Data <-------> Application Data - - Fig. 1. Message flow for a full handshake - - * Indicates optional or situation-dependent messages that are not - always sent. - - Note: To help avoid pipeline stalls, ChangeCipherSpec is an - independent TLS Protocol content type, and is not actually a TLS - handshake message. - - When the client and server decide to resume a previous session or - duplicate an existing session (instead of negotiating new security - parameters), the message flow is as follows: - - The client sends a ClientHello using the Session ID of the session to - be resumed. The server then checks its session cache for a match. If - a match is found, and the server is willing to re-establish the - connection under the specified session state, it will send a - ServerHello with the same Session ID value. At this point, both - client and server MUST send change cipher spec messages and proceed - directly to finished messages. Once the re-establishment is complete, - the client and server MAY begin to exchange application layer data. - (See flow chart below.) If a Session ID match is not found, the - server generates a new session ID and the TLS client and server - - - -Dierks & Rescorla Standards Track [Page 33] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - perform a full handshake. - - Client Server - - ClientHello --------> - ServerHello - [ChangeCipherSpec] - <-------- Finished - [ChangeCipherSpec] - Finished --------> - Application Data <-------> Application Data - - Fig. 2. Message flow for an abbreviated handshake - - The contents and significance of each message will be presented in - detail in the following sections. - -7.4. Handshake Protocol - - The TLS Handshake Protocol is one of the defined higher-level clients - of the TLS Record Protocol. This protocol is used to negotiate the - secure attributes of a session. Handshake messages are supplied to - the TLS Record Layer, where they are encapsulated within one or more - TLSPlaintext structures, which are processed and transmitted as - specified by the current active session state. - - enum { - hello_request(0), client_hello(1), server_hello(2), - certificate(11), server_key_exchange (12), - certificate_request(13), server_hello_done(14), - certificate_verify(15), client_key_exchange(16), - finished(20) - (255) - } HandshakeType; - - struct { - HandshakeType msg_type; /* handshake type */ - uint24 length; /* bytes in message */ - select (HandshakeType) { - case hello_request: HelloRequest; - case client_hello: ClientHello; - case server_hello: ServerHello; - case certificate: Certificate; - case server_key_exchange: ServerKeyExchange; - case certificate_request: CertificateRequest; - case server_hello_done: ServerHelloDone; - case certificate_verify: CertificateVerify; - case client_key_exchange: ClientKeyExchange; - - - -Dierks & Rescorla Standards Track [Page 34] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - case finished: Finished; - } body; - } Handshake; - - The handshake protocol messages are presented below in the order they - MUST be sent; sending handshake messages in an unexpected order - results in a fatal error. Unneeded handshake messages can be omitted, - however. Note one exception to the ordering: the Certificate message - is used twice in the handshake (from server to client, then from - client to server), but described only in its first position. The one - message that is not bound by these ordering rules is the Hello - Request message, which can be sent at any time, but which should be - ignored by the client if it arrives in the middle of a handshake. - - New Handshake message types are assigned by IANA as described in - Section 11. - -7.4.1. Hello Messages - - The hello phase messages are used to exchange security enhancement - capabilities between the client and server. When a new session - begins, the Record Layer's connection state encryption, hash, and - compression algorithms are initialized to null. The current - connection state is used for renegotiation messages. - -7.4.1.1. Hello Request - - When this message will be sent: - The hello request message MAY be sent by the server at any time. - - Meaning of this message: - Hello request is a simple notification that the client should - begin the negotiation process anew by sending a client hello - message when convenient. This message is not intended to - establish which side is the client or server but merely to - initiate a new negotiation. Servers SHOULD not send a - HelloRequest immediately upon the client's initial connection. - It is the client's job to send a ClientHello at that time. - - This message will be ignored by the client if the client is - currently negotiating a session. This message may be ignored by - the client if it does not wish to renegotiate a session, or the - client may, if it wishes, respond with a no_renegotiation alert. - Since handshake messages are intended to have transmission - precedence over application data, it is expected that the - negotiation will begin before no more than a few records are - received from the client. If the server sends a hello request but - does not receive a client hello in response, it may close the - - - -Dierks & Rescorla Standards Track [Page 35] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - connection with a fatal alert. - - After sending a hello request, servers SHOULD not repeat the request - until the subsequent handshake negotiation is complete. - - Structure of this message: - struct { } HelloRequest; - - Note: This message MUST NOT be included in the message hashes that are - maintained throughout the handshake and used in the finished - messages and the certificate verify message. - -7.4.1.2. Client Hello - - When this message will be sent: - When a client first connects to a server it is required to send - the client hello as its first message. The client can also send a - client hello in response to a hello request or on its own - initiative in order to renegotiate the security parameters in an - existing connection. - - Structure of this message: - The client hello message includes a random structure, which is - used later in the protocol. - - struct { - uint32 gmt_unix_time; - opaque random_bytes[28]; - } Random; - - gmt_unix_time - The current time and date in standard UNIX 32-bit format (seconds - since the midnight starting Jan 1, 1970, GMT, ignoring leap - seconds) according to the sender's internal clock. Clocks are not - required to be set correctly by the basic TLS Protocol; higher- - level or application protocols may define additional - requirements. - - random_bytes - 28 bytes generated by a secure random number generator. - - The client hello message includes a variable-length session - identifier. If not empty, the value identifies a session between the - same client and server whose security parameters the client wishes to - reuse. The session identifier MAY be from an earlier connection, this - connection, or from another currently active connection. The second - option is useful if the client only wishes to update the random - structures and derived values of a connection, and the third option - - - -Dierks & Rescorla Standards Track [Page 36] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - makes it possible to establish several independent secure connections - without repeating the full handshake protocol. These independent - connections may occur sequentially or simultaneously; a SessionID - becomes valid when the handshake negotiating it completes with the - exchange of Finished messages and persists until it is removed due to - aging or because a fatal error was encountered on a connection - associated with the session. The actual contents of the SessionID are - defined by the server. - - opaque SessionID<0..32>; - - Warning: - Because the SessionID is transmitted without encryption or - immediate MAC protection, servers MUST not place confidential - information in session identifiers or let the contents of fake - session identifiers cause any breach of security. (Note that the - content of the handshake as a whole, including the SessionID, is - protected by the Finished messages exchanged at the end of the - handshake.) - - The CipherSuite list, passed from the client to the server in the - client hello message, contains the combinations of cryptographic - algorithms supported by the client in order of the client's - preference (favorite choice first). Each CipherSuite defines a key - exchange algorithm, a bulk encryption algorithm (including secret key - length), a MAC algorithm, and a PRF. The server will select a cipher - suite or, if no acceptable choices are presented, return a handshake - failure alert and close the connection. - - uint8 CipherSuite[2]; /* Cryptographic suite selector */ - - The client hello includes a list of compression algorithms supported - by the client, ordered according to the client's preference. - - enum { null(0), (255) } CompressionMethod; - - struct { - ProtocolVersion client_version; - Random random; - SessionID session_id; - CipherSuite cipher_suites<2..2^16-1>; - CompressionMethod compression_methods<1..2^8-1>; - select (extensions_present) { - case false: - struct {}; - case true: - Extension extensions<0..2^16-1>; - } - - - -Dierks & Rescorla Standards Track [Page 37] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - } ClientHello; - - TLS allows extensions to follow the compression_methods field in an - extensions block. The presence of extensions can be detected by - determining whether there are bytes following the compression_methods - at the end of the ClientHello. Note that this method of detecting - optional data differs from the normal TLS method of having a - variable-length field but is used for compatibility with TLS before - extensions were defined. - - client_version - The version of the TLS protocol by which the client wishes to - communicate during this session. This SHOULD be the latest - (highest valued) version supported by the client. For this - version of the specification, the version will be 3.3 (See - Appendix E for details about backward compatibility). - - random - A client-generated random structure. - - session_id - The ID of a session the client wishes to use for this connection. - This field should be empty if no session_id is available, or it - the client wishes to generate new security parameters. - - cipher_suites - This is a list of the cryptographic options supported by the - client, with the client's first preference first. If the - session_id field is not empty (implying a session resumption - request) this vector MUST include at least the cipher_suite from - that session. Values are defined in Appendix A.5. - - compression_methods - This is a list of the compression methods supported by the - client, sorted by client preference. If the session_id field is - not empty (implying a session resumption request) it MUST include - the compression_method from that session. This vector MUST - contain, and all implementations MUST support, - CompressionMethod.null. Thus, a client and server will always be - able to agree on a compression method. - - client_hello_extension_list - Clients MAY request extended functionality from servers by - sending data in the client_hello_extension_list. Here the new - "client_hello_extension_list" field contains a list of - extensions. The actual "Extension" format is defined in Section - 7.4.1.4. - - - - -Dierks & Rescorla Standards Track [Page 38] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - In the event that a client requests additional functionality using - extensions, and this functionality is not supplied by the server, the - client MAY abort the handshake. A server that supports the - extensions mechanism MUST accept only client hello messages in either - the original (TLS 1.0/TLS 1.1) ClientHello or the extended - ClientHello format defined in this document, and (as for all other - messages) MUST check that the amount of data in the message precisely - matches one of these formats; if not then it MUST send a fatal - "decode_error" alert. - - After sending the client hello message, the client waits for a server - hello message. Any other handshake message returned by the server - except for a hello request is treated as a fatal error. - - -7.4.1.3. Server Hello - - - When this message will be sent: - The server will send this message in response to a client hello - message when it was able to find an acceptable set of algorithms. - If it cannot find such a match, it will respond with a handshake - failure alert. - - Structure of this message: - struct { - ProtocolVersion server_version; - Random random; - SessionID session_id; - CipherSuite cipher_suite; - CompressionMethod compression_method; - select (extensions_present) { - case false: - struct {}; - case true: - Extension extensions<0..2^16-1>; - } - } ServerHello; - - The presence of extensions can be detected by determining whether - there are bytes following the compression_method field at the end of - the ServerHello. - - server_version - This field will contain the lower of that suggested by the client - in the client hello and the highest supported by the server. For - this version of the specification, the version is 3.2. (See - Appendix E for details about backward compatibility.) - - - -Dierks & Rescorla Standards Track [Page 39] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - random - This structure is generated by the server and MUST be - independently generated from the ClientHello.random. - - session_id - This is the identity of the session corresponding to this - connection. If the ClientHello.session_id was non-empty, the - server will look in its session cache for a match. If a match is - found and the server is willing to establish the new connection - using the specified session state, the server will respond with - the same value as was supplied by the client. This indicates a - resumed session and dictates that the parties must proceed - directly to the finished messages. Otherwise this field will - contain a different value identifying the new session. The server - may return an empty session_id to indicate that the session will - not be cached and therefore cannot be resumed. If a session is - resumed, it must be resumed using the same cipher suite it was - originally negotiated with. Note that there is no requirement - that the server resume any session even if it had formerly - provided a session_id. Client MUST be prepared to do a full - negotiation -- including negotiating new cipher suites -- during - any handshake. - - cipher_suite - The single cipher suite selected by the server from the list in - ClientHello.cipher_suites. For resumed sessions, this field is - the value from the state of the session being resumed. - - compression_method - The single compression algorithm selected by the server from the - list in ClientHello.compression_methods. For resumed sessions - this field is the value from the resumed session state. - - server_hello_extension_list - A list of extensions. Note that only extensions offered by the - client can appear in the server's list. - -7.4.1.4 Hello Extensions - - The extension format is: - - struct { - ExtensionType extension_type; - opaque extension_data<0..2^16-1>; - } Extension; - - enum { - cert_hash_types(TBD-BY-IANA), (65535) - - - -Dierks & Rescorla Standards Track [Page 40] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - } ExtensionType; - - - Here: - - - "extension_type" identifies the particular extension type. - - - "extension_data" contains information specific to the particular - extension type. - - The list of extension types, as defined in Section 2.3, is maintained - by the Internet Assigned Numbers Authority (IANA). Thus an - application needs to be made to the IANA in order to obtain a new - extension type value. Since there are subtle (and not so subtle) - interactions that may occur in this protocol between new features and - existing features which may result in a significant reduction in - overall security, new values SHALL be defined only through the IETF - Consensus process specified in [IANA]. (This means that new - assignments can be made only via RFCs approved by the IESG.) The - initial set of extensions is defined in a companion document [TBD]. - - The following considerations should be taken into account when - designing new extensions: - - - Some cases where a server does not agree to an extension are - error - conditions, and some simply a refusal to support a particular - feature. In general error alerts should be used for the former, - and a field in the server extension response for the latter. - - - Extensions should as far as possible be designed to prevent any - attack that forces use (or non-use) of a particular feature by - manipulation of handshake messages. This principle should be - followed regardless of whether the feature is believed to cause a - security problem. - - Often the fact that the extension fields are included in the - inputs to the Finished message hashes will be sufficient, but - extreme care is needed when the extension changes the meaning of - messages sent in the handshake phase. Designers and implementors - should be aware of the fact that until the handshake has been - authenticated, active attackers can modify messages and insert, - remove, or replace extensions. - - - It would be technically possible to use extensions to change - major aspects of the design of TLS; for example the design of - cipher suite negotiation. This is not recommended; it would be - more appropriate to define a new version of TLS - particularly - - - -Dierks & Rescorla Standards Track [Page 41] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - since the TLS handshake algorithms have specific protection - against version rollback attacks based on the version number, and - the possibility of version rollback should be a significant - consideration in any major design change. - -7.4.1.4.1 Cert Hash Types - - The client MAY use the "cert_hash_types" to indicate to the - server which hash functions may be used in the signature on the - server's certificate. The "extension_data" field of this - extension contains: - - enum{ - md5(0), sha1(1), sha256(2), sha384(3), sha512(4), (255) - } HashType; - - struct { - HashType types<255>; - } CertHashTypes; - - These values indicate support for MD5 [MD5], SHA-1, SHA-256, SHA-384, - and SHA-512 [SHA] respectively. The server MUST NOT send this - extension. - - Clients SHOULD send this extension if they support any algorithm - other than SHA-1. If this extension is not used, servers SHOULD - assume that the client supports only SHA-1. Note: this is a change - from TLS 1.1 where there are no explicit rules but as a practical - matter one can assume that the peer supports MD5 and SHA-1. - -7.4.2. Server Certificate - - When this message will be sent: - The server MUST send a certificate whenever the agreed-upon key - exchange method uses certificates for authentication (this - includes all key exchange methods defined in this document except - DH_anon). This message will always immediately follow the server - hello message. - - Meaning of this message: - The certificate type MUST be appropriate for the selected cipher - suite's key exchange algorithm, and is generally an X.509v3 - certificate. It MUST contain a key that matches the key exchange - method, as follows. Unless otherwise specified, the signing - algorithm for the certificate MUST be the same as the algorithm - for the certificate key. Unless otherwise specified, the public - key MAY be of any length. - - - - -Dierks & Rescorla Standards Track [Page 42] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Key Exchange Algorithm Certificate Key Type - - RSA RSA public key; the certificate MUST - allow the key to be used for encryption. - - DHE_DSS DSS public key. - - DHE_RSA RSA public key that can be used for - signing. - - DH_DSS Diffie-Hellman key. The algorithm used - to sign the certificate MUST be DSS. - - DH_RSA Diffie-Hellman key. The algorithm used - to sign the certificate MUST be RSA. - - All certificate profiles, and key and cryptographic formats are - defined by the IETF PKIX working group [PKIX]. When a key usage - extension is present, the digitalSignature bit MUST be set for the - key to be eligible for signing, as described above, and the - keyEncipherment bit MUST be present to allow encryption, as described - above. The keyAgreement bit must be set on Diffie-Hellman - certificates. - - As CipherSuites that specify new key exchange methods are specified - for the TLS Protocol, they will imply certificate format and the - required encoded keying information. - - Structure of this message: - opaque ASN.1Cert<1..2^24-1>; - - struct { - ASN.1Cert certificate_list<0..2^24-1>; - } Certificate; - - certificate_list - This is a sequence (chain) of X.509v3 certificates. The sender's - certificate must come first in the list. Each following - certificate must directly certify the one preceding it. Because - certificate validation requires that root keys be distributed - independently, the self-signed certificate that specifies the - root certificate authority may optionally be omitted from the - chain, under the assumption that the remote end must already - possess it in order to validate it in any case. - - The same message type and structure will be used for the client's - response to a certificate request message. Note that a client MAY - send no certificates if it does not have an appropriate certificate - - - -Dierks & Rescorla Standards Track [Page 43] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - to send in response to the server's authentication request. - - Note: PKCS #7 [PKCS7] is not used as the format for the certificate - vector because PKCS #6 [PKCS6] extended certificates are not - used. Also, PKCS #7 defines a SET rather than a SEQUENCE, making - the task of parsing the list more difficult. - -7.4.3. Server Key Exchange Message - - When this message will be sent: - This message will be sent immediately after the server - certificate message (or the server hello message, if this is an - anonymous negotiation). - - The server key exchange message is sent by the server only when - the server certificate message (if sent) does not contain enough - data to allow the client to exchange a premaster secret. This is - true for the following key exchange methods: - - DHE_DSS - DHE_RSA - DH_anon - - It is not legal to send the server key exchange message for the - following key exchange methods: - - RSA - DH_DSS - DH_RSA - - Meaning of this message: - This message conveys cryptographic information to allow the - client to communicate the premaster secret: a Diffie-Hellman - public key with which the client can complete a key exchange - (with the result being the premaster secret) or a public key for - some other algorithm. - - As additional CipherSuites are defined for TLS that include new key - exchange algorithms, the server key exchange message will be sent if - and only if the certificate type associated with the key exchange - algorithm does not provide enough information for the client to - exchange a premaster secret. - - If the SignatureAlgorithm being used to sign the ServerKeyExchange - message is DSA, the hash function used MUST be SHA-1. If the - SignatureAlgorithm it must be the same hash function used in the - signature of the server's certificate (found in the Certificate) - message. This algorithm is denoted Hash below. Hash.length is the - - - -Dierks & Rescorla Standards Track [Page 44] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - length of the output of that algorithm. - - Structure of this message: - enum { diffie_hellman } KeyExchangeAlgorithm; - - struct { - opaque dh_p<1..2^16-1>; - opaque dh_g<1..2^16-1>; - opaque dh_Ys<1..2^16-1>; - } ServerDHParams; /* Ephemeral DH parameters */ - - dh_p - The prime modulus used for the Diffie-Hellman operation. - - dh_g - The generator used for the Diffie-Hellman operation. - - dh_Ys - The server's Diffie-Hellman public value (g^X mod p). - - struct { - select (KeyExchangeAlgorithm) { - case diffie_hellman: - ServerDHParams params; - Signature signed_params; - }; - } ServerKeyExchange; - - struct { - select (KeyExchangeAlgorithm) { - case diffie_hellman: - ServerDHParams params; - }; - } ServerParams; - - params - The server's key exchange parameters. - - signed_params - For non-anonymous key exchanges, a hash of the corresponding - params value, with the signature appropriate to that hash - applied. - - hash - Hash(ClientHello.random + ServerHello.random + ServerParams) - - sha_hash - SHA1(ClientHello.random + ServerHello.random + ServerParams) - - - -Dierks & Rescorla Standards Track [Page 45] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - enum { anonymous, rsa, dsa } SignatureAlgorithm; - - - struct { - select (SignatureAlgorithm) { - case anonymous: struct { }; - case rsa: - digitally-signed struct { - opaque hash[Hash.length]; - }; - case dsa: - digitally-signed struct { - opaque sha_hash[20]; - }; - }; - }; - } Signature; - -7.4.4. Certificate Request - - When this message will be sent: - A non-anonymous server can optionally request a certificate from - the client, if appropriate for the selected cipher suite. This - message, if sent, will immediately follow the Server Key Exchange - message (if it is sent; otherwise, the Server Certificate - message). - - Structure of this message: - enum { - rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), - rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), - fortezza_dms_RESERVED(20), - (255) - } ClientCertificateType; - - - opaque DistinguishedName<1..2^16-1>; - - struct { - ClientCertificateType certificate_types<1..2^8-1>; - HashType certificate_hash<1..2^8-1>; - DistinguishedName certificate_authorities<0..2^16-1>; - } CertificateRequest; - - certificate_types - This field is a list of the types of certificates requested, - sorted in order of the server's preference. - - - - -Dierks & Rescorla Standards Track [Page 46] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - certificate_types - A list of the types of certificate types which the client may - offer. - rsa_sign a certificate containing an RSA key - dss_sign a certificate containing a DSS key - rsa_fixed_dh a certificate signed with RSA and containing - a static DH key. - dss_fixed_dh a certificate signed with DSS and containing - a static DH key - - Certificate types rsa_sign and dss_sign SHOULD contain - certificates signed with the same algorithm. However, this is - not required. This is a holdover from TLS 1.0 and 1.1. - - - certificate_hash - A list of acceptable hash algorithms to be used in - certificate signatures. - - certificate_authorities - A list of the distinguished names of acceptable certificate - authorities. These distinguished names may specify a desired - distinguished name for a root CA or for a subordinate CA; - thus, this message can be used both to describe known roots - and a desired authorization space. If the - certificate_authorities list is empty then the client MAY - send any certificate of the appropriate - ClientCertificateType, unless there is some external - arrangement to the contrary. - - New ClientCertificateType values are assigned by IANA as described in - Section 11. - - Note: Values listed as RESERVED may not be used. They were - used in SSLv3. - - - Note: DistinguishedName is derived from [X501]. DistinguishedNames are - represented in DER-encoded format. - - Note: It is a fatal handshake_failure alert for an anonymous server to - request client authentication. - -7.4.5 Server hello done - - When this message will be sent: - The server hello done message is sent by the server to indicate - the end of the server hello and associated messages. After - - - -Dierks & Rescorla Standards Track [Page 47] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - sending this message, the server will wait for a client response. - - Meaning of this message: - This message means that the server is done sending messages to - support the key exchange, and the client can proceed with its - phase of the key exchange. - - Upon receipt of the server hello done message, the client SHOULD - verify that the server provided a valid certificate, if required - and check that the server hello parameters are acceptable. - - Structure of this message: - struct { } ServerHelloDone; - -7.4.6. Client Certificate - - When this message will be sent: - This is the first message the client can send after receiving a - server hello done message. This message is only sent if the - server requests a certificate. If no suitable certificate is - available, the client SHOULD send a certificate message - containing no certificates. That is, the certificate_list - structure has a length of zero. If client authentication is - required by the server for the handshake to continue, it may - respond with a fatal handshake failure alert. Client certificates - are sent using the Certificate structure defined in Section - 7.4.2. - - - Note: When using a static Diffie-Hellman based key exchange method - (DH_DSS or DH_RSA), if client authentication is requested, the - Diffie-Hellman group and generator encoded in the client's - certificate MUST match the server specified Diffie-Hellman - parameters if the client's parameters are to be used for the key - exchange. - -7.4.7. Client Key Exchange Message - - When this message will be sent: - This message is always sent by the client. It MUST immediately - follow the client certificate message, if it is sent. Otherwise - it MUST be the first message sent by the client after it receives - the server hello done message. - - Meaning of this message: - With this message, the premaster secret is set, either though - direct transmission of the RSA-encrypted secret, or by the - transmission of Diffie-Hellman parameters that will allow each - - - -Dierks & Rescorla Standards Track [Page 48] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - side to agree upon the same premaster secret. When the key - exchange method is DH_RSA or DH_DSS, client certification has - been requested, and the client was able to respond with a - certificate that contained a Diffie-Hellman public key whose - parameters (group and generator) matched those specified by the - server in its certificate, this message MUST not contain any - data. - - Structure of this message: - The choice of messages depends on which key exchange method has - been selected. See Section 7.4.3 for the KeyExchangeAlgorithm - definition. - - struct { - select (KeyExchangeAlgorithm) { - case rsa: EncryptedPreMasterSecret; - case diffie_hellman: ClientDiffieHellmanPublic; - } exchange_keys; - } ClientKeyExchange; - -7.4.7.1. RSA Encrypted Premaster Secret Message - - Meaning of this message: - If RSA is being used for key agreement and authentication, the - client generates a 48-byte premaster secret, encrypts it using - the public key from the server's certificate and sends the result - in an encrypted premaster secret message. This structure is a - variant of the client key exchange message and is not a message - in itself. - - Structure of this message: - struct { - ProtocolVersion client_version; - opaque random[46]; - } PreMasterSecret; - - client_version - The latest (newest) version supported by the client. This is - used to detect version roll-back attacks. Upon receiving the - premaster secret, the server SHOULD check that this value - matches the value transmitted by the client in the client - hello message. - - random - 46 securely-generated random bytes. - - struct { - public-key-encrypted PreMasterSecret pre_master_secret; - - - -Dierks & Rescorla Standards Track [Page 49] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - } EncryptedPreMasterSecret; - - pre_master_secret - This random value is generated by the client and is used to - generate the master secret, as specified in Section 8.1. - - An attack discovered by Daniel Bleichenbacher [BLEI] can be used to - attack a TLS server which is using PKCS#1 v 1.5 encoded RSA. The - attack takes advantage of the fact that by failing in different ways, - a TLS server can be coerced into revealing whether a particular - message, when decrypted, is properly PKCS#1 v1.5 formatted or not. - - In order to avoid this vulnerability, implementations MUST treat - incorrectly formatted messages in a manner indistinguishable from - correctly formatted RSA blocks. Thus, when it receives an incorrectly - formatted RSA block, a server should generate a random 48-byte value - and proceed using it as the premaster secret. Thus, the server will - act identically whether the received RSA block is correctly encoded - or not. - - [PKCS1B] defines a newer version of PKCS#1 encoding that is more - secure against the Bleichenbacher attack. However, for maximal - compatibility with TLS 1.0, TLS 1.1 retains the original encoding. No - variants of the Bleichenbacher attack are known to exist provided - that the above recommendations are followed. - - Implementation Note: Public-key-encrypted data is represented as an - opaque vector <0..2^16-1> (see Section 4.7). Thus, the RSA-encrypted - PreMasterSecret in a ClientKeyExchange is preceded by two length - bytes. These bytes are redundant in the case of RSA because the - EncryptedPreMasterSecret is the only data in the ClientKeyExchange - and its length can therefore be unambiguously determined. The SSLv3 - specification was not clear about the encoding of public-key- - encrypted data, and therefore many SSLv3 implementations do not - include the the length bytes, encoding the RSA encrypted data - directly in the ClientKeyExchange message. - - This specification requires correct encoding of the - EncryptedPreMasterSecret complete with length bytes. The resulting - PDU is incompatible with many SSLv3 implementations. Implementors - upgrading from SSLv3 MUST modify their implementations to generate - and accept the correct encoding. Implementors who wish to be - compatible with both SSLv3 and TLS should make their implementation's - behavior dependent on the protocol version. - - Implementation Note: It is now known that remote timing-based attacks - on SSL are possible, at least when the client and server are on the - same LAN. Accordingly, implementations that use static RSA keys MUST - - - -Dierks & Rescorla Standards Track [Page 50] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - use RSA blinding or some other anti-timing technique, as described in - [TIMING]. - - Note: The version number in the PreMasterSecret MUST be the version - offered by the client in the ClientHello.version, not the version - negotiated for the connection. This feature is designed to prevent - rollback attacks. Unfortunately, many implementations use the - negotiated version instead and therefore checking the version number - may lead to failure to interoperate with such incorrect client - implementations. Client implementations MUST and Server - implementations MAY check the version number. In practice, since the - TLS handshake MACs prevent downgrade and no good attacks are known on - those MACs, ambiguity is not considered a serious security risk. - Note that if servers choose to to check the version number, they MUST - randomize the PreMasterSecret in case of error, rather than generate - an alert, in order to avoid variants on the Bleichenbacher attack. - [KPR03] - -7.4.7.1. Client Diffie-Hellman Public Value - - Meaning of this message: - This structure conveys the client's Diffie-Hellman public value - (Yc) if it was not already included in the client's certificate. - The encoding used for Yc is determined by the enumerated - PublicValueEncoding. This structure is a variant of the client - key exchange message, and not a message in itself. - - Structure of this message: - enum { implicit, explicit } PublicValueEncoding; - - implicit - If the client certificate already contains a suitable Diffie- - Hellman key, then Yc is implicit and does not need to be sent - again. In this case, the client key exchange message will be - sent, but it MUST be empty. - - explicit - Yc needs to be sent. - - struct { - select (PublicValueEncoding) { - case implicit: struct { }; - case explicit: opaque dh_Yc<1..2^16-1>; - } dh_public; - } ClientDiffieHellmanPublic; - - dh_Yc - The client's Diffie-Hellman public value (Yc). - - - -Dierks & Rescorla Standards Track [Page 51] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -7.4.8. Certificate verify - - When this message will be sent: - This message is used to provide explicit verification of a client - certificate. This message is only sent following a client - certificate that has signing capability (i.e. all certificates - except those containing fixed Diffie-Hellman parameters). When - sent, it MUST immediately follow the client key exchange message. - - Structure of this message: - struct { - Signature signature; - } CertificateVerify; - - The Signature type is defined in 7.4.3. If the SignatureAlgorithm - is DSA, then the sha_hash value must be used. If it is RSA, - the same function (denoted Hash) must be used as was used to - create the signature for the client's certificate. - - CertificateVerify.signature.hash - Hash(handshake_messages); - - CertificateVerify.signature.sha_hash - SHA(handshake_messages); - - Here handshake_messages refers to all handshake messages sent or - received starting at client hello up to but not including this - message, including the type and length fields of the handshake - messages. This is the concatenation of all the Handshake structures - as defined in 7.4 exchanged thus far. - -7.4.9. Finished - - When this message will be sent: - A finished message is always sent immediately after a change - cipher spec message to verify that the key exchange and - authentication processes were successful. It is essential that a - change cipher spec message be received between the other - handshake messages and the Finished message. - - Meaning of this message: - The finished message is the first protected with the just- - negotiated algorithms, keys, and secrets. Recipients of finished - messages MUST verify that the contents are correct. Once a side - has sent its Finished message and received and validated the - Finished message from its peer, it may begin to send and receive - application data over the connection. - - - - -Dierks & Rescorla Standards Track [Page 52] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - struct { - opaque verify_data[12]; - } Finished; - - verify_data - PRF(master_secret, finished_label, Hash(handshake_messages))[0..11]; - - finished_label - For Finished messages sent by the client, the string "client - finished". For Finished messages sent by the server, the - string "server finished". - - Hash denotes the negotiated hash used for the PRF. If a new - PRF is defined, then this hash MUST be specified. - - handshake_messages - All of the data from all messages in this handshake (not - including any HelloRequest messages) up to but not including - this message. This is only data visible at the handshake - layer and does not include record layer headers. This is the - concatenation of all the Handshake structures as defined in - 7.4, exchanged thus far. - - It is a fatal error if a finished message is not preceded by a change - cipher spec message at the appropriate point in the handshake. - - The value handshake_messages includes all handshake messages starting - at client hello up to, but not including, this finished message. This - may be different from handshake_messages in Section 7.4.9 because it - would include the certificate verify message (if sent). Also, the - handshake_messages for the finished message sent by the client will - be different from that for the finished message sent by the server, - because the one that is sent second will include the prior one. - - Note: Change cipher spec messages, alerts and, any other record types - are not handshake messages and are not included in the hash - computations. Also, Hello Request messages are omitted from - handshake hashes. - -8. Cryptographic Computations - - In order to begin connection protection, the TLS Record Protocol - requires specification of a suite of algorithms, a master secret, and - the client and server random values. The authentication, encryption, - and MAC algorithms are determined by the cipher_suite selected by the - server and revealed in the server hello message. The compression - algorithm is negotiated in the hello messages, and the random values - are exchanged in the hello messages. All that remains is to calculate - - - -Dierks & Rescorla Standards Track [Page 53] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - the master secret. - -8.1. Computing the Master Secret - - For all key exchange methods, the same algorithm is used to convert - the pre_master_secret into the master_secret. The pre_master_secret - should be deleted from memory once the master_secret has been - computed. - - master_secret = PRF(pre_master_secret, "master secret", - ClientHello.random + ServerHello.random) - [0..47]; - - The master secret is always exactly 48 bytes in length. The length of - the premaster secret will vary depending on key exchange method. - -8.1.1. RSA - - When RSA is used for server authentication and key exchange, a - 48-byte pre_master_secret is generated by the client, encrypted under - the server's public key, and sent to the server. The server uses its - private key to decrypt the pre_master_secret. Both parties then - convert the pre_master_secret into the master_secret, as specified - above. - -8.1.2. Diffie-Hellman - - A conventional Diffie-Hellman computation is performed. The - negotiated key (Z) is used as the pre_master_secret, and is converted - into the master_secret, as specified above. Leading bytes of Z that - contain all zero bits are stripped before it is used as the - pre_master_secret. - - Note: Diffie-Hellman parameters are specified by the server and may - be either ephemeral or contained within the server's certificate. - -9. Mandatory Cipher Suites - - In the absence of an application profile standard specifying - otherwise, a TLS compliant application MUST implement the cipher - suite TLS_RSA_WITH_3DES_EDE_CBC_SHA. - -10. Application Data Protocol - - Application data messages are carried by the Record Layer and are - fragmented, compressed and encrypted based on the current connection - state. The messages are treated as transparent data to the record - layer. - - - -Dierks & Rescorla Standards Track [Page 54] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -11. Security Considerations - - Security issues are discussed throughoutthis memo, especially in - Appendices D, E, and F. - -12. IANA Considerations - - This document uses several registries that were originally created in - [RFC4346]. IANA is requested to update (has updated) these to - reference this document. The registries and their allocation policies - (unchanged from [RFC4346]) are listed below. - - o TLS ClientCertificateType Identifiers Registry: Future - values in the range 0-63 (decimal) inclusive are assigned via - Standards Action [RFC2434]. Values in the range 64-223 - (decimal) inclusive are assigned Specification Required - [RFC2434]. Values from 224-255 (decimal) inclusive are - reserved for Private Use [RFC2434]. - - o TLS Cipher Suite Registry: Future values with the first byte - in the range 0-191 (decimal) inclusive are assigned via - Standards Action [RFC2434]. Values with the first byte in - the range 192-254 (decimal) are assigned via Specification - Required [RFC2434]. Values with the first byte 255 (decimal) - are reserved for Private Use [RFC2434]. - - o TLS ContentType Registry: Future values are allocated via - Standards Action [RFC2434]. - - o TLS Alert Registry: Future values are allocated via - Standards Action [RFC2434]. - - o TLS HandshakeType Registry: Future values are allocated via - Standards Action [RFC2434]. - - This document also uses a registry originally created in [RFC4366]. - IANA is requested to update (has updated) it to reference this - document. The registry and its allocation policy (unchanged from - [RFC4366]) is listed below:. - - o TLS ExtensionType Registry: Future values are allocated - via IETF Consensus [RFC2434] - - In addition, this document defines one new registry to be maintained - by IANA: - - o TLS HashType Registry: The registry will be initially - populated with the values described in Section 7.4.1.4.7. - - - -Dierks & Rescorla Standards Track [Page 55] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Future values in the range 0-63 (decimal) inclusive are - assigned via Standards Action [RFC2434]. Values in the - range 64-223 (decimal) inclusive are assigned via - Specification Required [RFC2434]. Values from 224-255 - (decimal) inclusive are reserved for Private Use [RFC2434]. - - This document defines one new TLS extension, cert_hash_type, which is - to be (has been) allocated value TBD-BY-IANA in the TLS ExtensionType - registry. - - -12.1 Extensions - - Section 11 describes a registry of ExtensionType values to be - maintained by the IANA. ExtensionType values are to be assigned via - IETF Consensus as defined in RFC 2434 [IANA]. The initial registry - corresponds to the definition of "ExtensionType" in Section 2.3. - - The MIME type "application/pkix-pkipath" has been registered by the - IANA with the following template: - - To: ietf-types@iana.org Subject: Registration of MIME media type - application/pkix-pkipath - - MIME media type name: application - MIME subtype name: pkix-pkipath - - Optional parameters: version (default value is "1") - - Encoding considerations: - This MIME type is a DER encoding of the ASN.1 type PkiPath, - defined as follows: - PkiPath ::= SEQUENCE OF Certificate - PkiPath is used to represent a certification path. Within the - sequence, the order of certificates is such that the subject of - the first certificate is the issuer of the second certificate, - etc. - - This is identical to the definition published in [X509-4th-TC1]; - note that it is different from that in [X509-4th]. - - All Certificates MUST conform to [PKIX]. (This should be - interpreted as a requirement to encode only PKIX-conformant - certificates using this type. It does not necessarily require - that all certificates that are not strictly PKIX-conformant must - be rejected by relying parties, although the security consequences - of accepting any such certificates should be considered - carefully.) - - - -Dierks & Rescorla Standards Track [Page 56] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - DER (as opposed to BER) encoding MUST be used. If this type is - sent over a 7-bit transport, base64 encoding SHOULD be used. - - Security considerations: - The security considerations of [X509-4th] and [PKIX] (or any - updates to them) apply, as well as those of any protocol that uses - this type (e.g., TLS). - - Note that this type only specifies a certificate chain that can be - assessed for validity according to the relying party's existing - configuration of trusted CAs; it is not intended to be used to - specify any change to that configuration. - - Interoperability considerations: - No specific interoperability problems are known with this type, - but for recommendations relating to X.509 certificates in general, - see [PKIX]. - - Published specification: this memo, and [PKIX]. - - Applications which use this media type: TLS. It may also be used by - other protocols, or for general interchange of PKIX certificate - - Additional information: - Magic number(s): DER-encoded ASN.1 can be easily recognized. - Further parsing is required to distinguish from other ASN.1 - types. - File extension(s): .pkipath - Macintosh File Type Code(s): not specified - - Person & email address to contact for further information: - Magnus Nystrom <magnus@rsasecurity.com> - - Intended usage: COMMON - - Change controller: - IESG <iesg@ietf.org> - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 57] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix A. Protocol Constant Values - - This section describes protocol types and constants. - -A.1. Record Layer - - struct { - uint8 major, minor; - } ProtocolVersion; - - ProtocolVersion version = { 3, 3 }; /* TLS v1.2*/ - - enum { - change_cipher_spec(20), alert(21), handshake(22), - application_data(23), (255) - } ContentType; - - struct { - ContentType type; - ProtocolVersion version; - uint16 length; - opaque fragment[TLSPlaintext.length]; - } TLSPlaintext; - - struct { - ContentType type; - ProtocolVersion version; - uint16 length; - opaque fragment[TLSCompressed.length]; - } TLSCompressed; - - struct { - ContentType type; - ProtocolVersion version; - uint16 length; - select (SecurityParameters.cipher_type) { - case stream: GenericStreamCipher; - case block: GenericBlockCipher; - case aead: GenericAEADCipher; - } fragment; - } TLSCiphertext; - - stream-ciphered struct { - opaque content[TLSCompressed.length]; - opaque MAC[SecurityParameters.mac_length]; - } GenericStreamCipher; - - block-ciphered struct { - - - -Dierks & Rescorla Standards Track [Page 58] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - opaque IV[SecurityParameters.block_length]; - opaque content[TLSCompressed.length]; - opaque MAC[SecurityParameters.mac_length]; - uint8 padding[GenericBlockCipher.padding_length]; - uint8 padding_length; - } GenericBlockCipher; - - aead-ciphered struct { - opaque IV[SecurityParameters.iv_length]; - opaque aead_output[AEADEncrypted.length]; - } GenericAEADCipher; - -A.2. Change Cipher Specs Message - - struct { - enum { change_cipher_spec(1), (255) } type; - } ChangeCipherSpec; - -A.3. Alert Messages - - enum { warning(1), fatal(2), (255) } AlertLevel; - - enum { - close_notify(0), - unexpected_message(10), - bad_record_mac(20), - decryption_failed(21), - record_overflow(22), - decompression_failure(30), - handshake_failure(40), - no_certificate_RESERVED (41), - bad_certificate(42), - unsupported_certificate(43), - certificate_revoked(44), - certificate_expired(45), - certificate_unknown(46), - illegal_parameter(47), - unknown_ca(48), - access_denied(49), - decode_error(50), - decrypt_error(51), - export_restriction_RESERVED(60), - protocol_version(70), - insufficient_security(71), - internal_error(80), - user_canceled(90), - no_renegotiation(100), - unsupported_extension(110), /* new */ - - - -Dierks & Rescorla Standards Track [Page 59] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - (255) - } AlertDescription; - - struct { - AlertLevel level; - AlertDescription description; - } Alert; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 60] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -A.4. Handshake Protocol - - enum { - hello_request(0), client_hello(1), server_hello(2), - certificate(11), server_key_exchange (12), - certificate_request(13), server_hello_done(14), - certificate_verify(15), client_key_exchange(16), - finished(20) - (255) - } HandshakeType; - - struct { - HandshakeType msg_type; - uint24 length; - select (HandshakeType) { - case hello_request: HelloRequest; - case client_hello: ClientHello; - case server_hello: ServerHello; - case certificate: Certificate; - case server_key_exchange: ServerKeyExchange; - case certificate_request: CertificateRequest; - case server_hello_done: ServerHelloDone; - case certificate_verify: CertificateVerify; - case client_key_exchange: ClientKeyExchange; - case finished: Finished; - } body; - } Handshake; - -A.4.1. Hello Messages - - struct { } HelloRequest; - - struct { - uint32 gmt_unix_time; - opaque random_bytes[28]; - } Random; - - opaque SessionID<0..32>; - - uint8 CipherSuite[2]; - - enum { null(0), (255) } CompressionMethod; - - struct { - ProtocolVersion client_version; - Random random; - SessionID session_id; - CipherSuite cipher_suites<2..2^16-1>; - - - -Dierks & Rescorla Standards Track [Page 61] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - CompressionMethod compression_methods<1..2^8-1>; - Extension client_hello_extension_list<0..2^16-1>; - } ClientHello; - - struct { - ProtocolVersion server_version; - Random random; - SessionID session_id; - CipherSuite cipher_suite; - CompressionMethod compression_method; - } ServerHello; - - struct { - ExtensionType extension_type; - opaque extension_data<0..2^16-1>; - } Extension; - - enum { - cert_hash_types(TBD-BY-IANA), (65535) - } ExtensionType; - -A.4.2. Server Authentication and Key Exchange Messages - - opaque ASN.1Cert<2^24-1>; - - struct { - ASN.1Cert certificate_list<0..2^24-1>; - } Certificate; - - struct { - CertificateStatusType status_type; - select (status_type) { - case ocsp: OCSPResponse; - } response; - } CertificateStatus; - - opaque OCSPResponse<1..2^24-1>; - - enum { diffie_hellman } KeyExchangeAlgorithm; - - struct { - opaque dh_p<1..2^16-1>; - opaque dh_g<1..2^16-1>; - opaque dh_Ys<1..2^16-1>; - } ServerDHParams; - - struct { - select (KeyExchangeAlgorithm) { - - - -Dierks & Rescorla Standards Track [Page 62] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - case diffie_hellman: - ServerDHParams params; - Signature signed_params; - } ServerKeyExchange; - - enum { anonymous, rsa, dsa } SignatureAlgorithm; - - struct { - select (KeyExchangeAlgorithm) { - case diffie_hellman: - ServerDHParams params; - }; - } ServerParams; - - struct { - select (SignatureAlgorithm) { - case anonymous: struct { }; - case rsa: - digitally-signed struct { - opaque hash[Hash.length]; - }; - case dsa: - digitally-signed struct { - opaque sha_hash[20]; - }; - }; - }; - } Signature; - - enum { - rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), - rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), - fortezza_dms_RESERVED(20), - (255) - } ClientCertificateType; - - opaque DistinguishedName<1..2^16-1>; - - struct { - ClientCertificateType certificate_types<1..2^8-1>; - DistinguishedName certificate_authorities<0..2^16-1>; - } CertificateRequest; - - struct { } ServerHelloDone; - -A.4.3. Client Authentication and Key Exchange Messages - - struct { - - - -Dierks & Rescorla Standards Track [Page 63] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - select (KeyExchangeAlgorithm) { - case rsa: EncryptedPreMasterSecret; - case diffie_hellman: ClientDiffieHellmanPublic; - } exchange_keys; - } ClientKeyExchange; - - struct { - ProtocolVersion client_version; - opaque random[46]; - } PreMasterSecret; - - struct { - public-key-encrypted PreMasterSecret pre_master_secret; - } EncryptedPreMasterSecret; - - enum { implicit, explicit } PublicValueEncoding; - - struct { - select (PublicValueEncoding) { - case implicit: struct {}; - case explicit: opaque DH_Yc<1..2^16-1>; - } dh_public; - } ClientDiffieHellmanPublic; - - struct { - Signature signature; - } CertificateVerify; - -A.4.4. Handshake Finalization Message - - struct { - opaque verify_data[12]; - } Finished; - -A.5. The CipherSuite - - The following values define the CipherSuite codes used in the client - hello and server hello messages. - - A CipherSuite defines a cipher specification supported in TLS Version - 1.1. - - TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a - TLS connection during the first handshake on that channel, but MUST - not be negotiated, as it provides no more protection than an - unsecured connection. - - CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 }; - - - -Dierks & Rescorla Standards Track [Page 64] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - The following CipherSuite definitions require that the server provide - an RSA certificate that can be used for key exchange. The server may - request either an RSA or a DSS signature-capable certificate in the - certificate request message. - - CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 }; - CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 }; - CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 }; - CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 }; - CipherSuite TLS_RSA_WITH_IDEA_CBC_SHA = { 0x00,0x07 }; - CipherSuite TLS_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 }; - CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A }; - CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F }; - CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x35 }; - - The following CipherSuite definitions are used for server- - authenticated (and optionally client-authenticated) Diffie-Hellman. - DH denotes cipher suites in which the server's certificate contains - the Diffie-Hellman parameters signed by the certificate authority - (CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman - parameters are signed by a DSS or RSA certificate, which has been - signed by the CA. The signing algorithm used is specified after the - DH or DHE parameter. The server can request an RSA or DSS signature- - capable certificate from the client for client authentication or it - may request a Diffie-Hellman certificate. Any Diffie-Hellman - certificate provided by the client must use the parameters (group and - generator) described by the server. - - CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C }; - CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; - CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F }; - CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; - CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 }; - CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; - CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 }; - CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 }; - CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x30 }; - CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x31 }; - CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x32 }; - CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x33 }; - CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x36 }; - CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x37 }; - CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x38 }; - CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x39 }; - - The following cipher suites are used for completely anonymous Diffie- - Hellman communications in which neither party is authenticated. Note - that this mode is vulnerable to man-in-the-middle attacks. Using - - - -Dierks & Rescorla Standards Track [Page 65] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - this mode therefore is of limited use: These ciphersuites MUST NOT be - used by TLS 1.2 implementations unless the application layer has - specifically requested to allow anonymous key exchange. (Anonymous - key exchange may sometimes be acceptable, for example, to support - opportunistic encryption when no set-up for authentication is in - place, or when TLS is used as part of more complex security protocols - that have other means to ensure authentication.) - - CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00, 0x18 }; - CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA = { 0x00, 0x1A }; - CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x1B }; - CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x34 }; - CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00, 0x3A }; - - Note that using non-anonymous key exchange without actually verifying - the key exchange is essentially equivalent to anonymous key exchange, - and the same precautions apply. While non-anonymous key exchange - will generally involve a higher computational and communicational - cost than anonymous key exchange, it may be in the interest of - interoperability not to disable non-anonymous key exchange when the - application layer is allowing anonymous key exchange. - - When SSLv3 and TLS 1.0 were designed, the United States restricted - the export of cryptographic software containing certain strong - encryption algorithms. A series of cipher suites were designed to - operate at reduced key lengths in order to comply with those - regulations. Due to advances in computer performance, these - algorithms are now unacceptably weak and export restrictions have - since been loosened. TLS 1.2 implementations MUST NOT negotiate these - cipher suites in TLS 1.2 mode. However, for backward compatibility - they may be offered in the ClientHello for use with TLS 1.0 or SSLv3 - only servers. TLS 1.2 clients MUST check that the server did not - choose one of these cipher suites during the handshake. These - ciphersuites are listed below for informational purposes and to - reserve the numbers. - - CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 }; - CipherSuite TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x06 }; - CipherSuite TLS_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x08 }; - CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B }; - CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E }; - CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 }; - CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 }; - CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 }; - CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 }; - - The following cipher suites were defined in [TLSKRB] and are included - here for completeness. See [TLSKRB] for details: - - - -Dierks & Rescorla Standards Track [Page 66] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - CipherSuite TLS_KRB5_WITH_DES_CBC_SHA = { 0x00,0x1E }; - CipherSuite TLS_KRB5_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1F }; - CipherSuite TLS_KRB5_WITH_RC4_128_SHA = { 0x00,0x20 }; - CipherSuite TLS_KRB5_WITH_IDEA_CBC_SHA = { 0x00,0x21 }; - CipherSuite TLS_KRB5_WITH_DES_CBC_MD5 = { 0x00,0x22 }; - CipherSuite TLS_KRB5_WITH_3DES_EDE_CBC_MD5 = { 0x00,0x23 }; - CipherSuite TLS_KRB5_WITH_RC4_128_MD5 = { 0x00,0x24 }; - CipherSuite TLS_KRB5_WITH_IDEA_CBC_MD5 = { 0x00,0x25 }; - - The following exportable cipher suites were defined in [TLSKRB] and - are included here for completeness. TLS 1.2 implementations MUST NOT - negotiate these cipher suites. - - CipherSuite TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA = { 0x00,0x26 - }; - CipherSuite TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA = { 0x00,0x27 - }; - CipherSuite TLS_KRB5_EXPORT_WITH_RC4_40_SHA = { 0x00,0x28 - }; - CipherSuite TLS_KRB5_EXPORT_WITH_DES_CBC_40_MD5 = { 0x00,0x29 - }; - CipherSuite TLS_KRB5_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x2A - }; - CipherSuite TLS_KRB5_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x2B - }; - - - New cipher suite values are assigned by IANA as described in Section - 11. - - Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are - reserved to avoid collision with Fortezza-based cipher suites in SSL - 3. - -A.6. The Security Parameters - - These security parameters are determined by the TLS Handshake - Protocol and provided as parameters to the TLS Record Layer in order - to initialize a connection state. SecurityParameters includes: - - enum { null(0), (255) } CompressionMethod; - - enum { server, client } ConnectionEnd; - - enum { null, rc4, rc2, des, 3des, des40, aes, idea } - BulkCipherAlgorithm; - - enum { stream, block } CipherType; - - - -Dierks & Rescorla Standards Track [Page 67] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - enum { null, md5, sha } MACAlgorithm; - - /* The algorithms specified in CompressionMethod, - BulkCipherAlgorithm, and MACAlgorithm may be added to. */ - - struct { - ConnectionEnd entity; - BulkCipherAlgorithm bulk_cipher_algorithm; - CipherType cipher_type; - uint8 enc_key_length; - uint8 block_length; - uint8 iv_length; - MACAlgorithm mac_algorithm; - uint8 mac_length; - uint8 mac_key_length; - CompressionMethod compression_algorithm; - opaque master_secret[48]; - opaque client_random[32]; - opaque server_random[32]; - } SecurityParameters; - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 68] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix B. Glossary - - Advanced Encryption Standard (AES) - AES is a widely used symmetric encryption algorithm. AES is a - block cipher with a 128, 192, or 256 bit keys and a 16 byte block - size. [AES] TLS currently only supports the 128 and 256 bit key - sizes. - - application protocol - An application protocol is a protocol that normally layers - directly on top of the transport layer (e.g., TCP/IP). Examples - include HTTP, TELNET, FTP, and SMTP. - - asymmetric cipher - See public key cryptography. - - authenticated encryption with additional data (AEAD) - A symmetric encryption algorithm that simultaneously provides - confidentiality and message integrity. - - authentication - Authentication is the ability of one entity to determine the - identity of another entity. - - block cipher - A block cipher is an algorithm that operates on plaintext in - groups of bits, called blocks. 64 bits is a common block size. - - bulk cipher - A symmetric encryption algorithm used to encrypt large quantities - of data. - - cipher block chaining (CBC) - CBC is a mode in which every plaintext block encrypted with a - block cipher is first exclusive-ORed with the previous ciphertext - block (or, in the case of the first block, with the - initialization vector). For decryption, every block is first - decrypted, then exclusive-ORed with the previous ciphertext block - (or IV). - - certificate - As part of the X.509 protocol (a.k.a. ISO Authentication - framework), certificates are assigned by a trusted Certificate - Authority and provide a strong binding between a party's identity - or some other attributes and its public key. - - client - The application entity that initiates a TLS connection to a - - - -Dierks & Rescorla Standards Track [Page 69] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - server. This may or may not imply that the client initiated the - underlying transport connection. The primary operational - difference between the server and client is that the server is - generally authenticated, while the client is only optionally - authenticated. - - client write key - The key used to encrypt data written by the client. - - client write MAC secret - The secret data used to authenticate data written by the client. - - connection - A connection is a transport (in the OSI layering model - definition) that provides a suitable type of service. For TLS, - such connections are peer-to-peer relationships. The connections - are transient. Every connection is associated with one session. - - Data Encryption Standard - DES is a very widely used symmetric encryption algorithm. DES is - a block cipher with a 56 bit key and an 8 byte block size. Note - that in TLS, for key generation purposes, DES is treated as - having an 8 byte key length (64 bits), but it still only provides - 56 bits of protection. (The low bit of each key byte is presumed - to be set to produce odd parity in that key byte.) DES can also - be operated in a mode where three independent keys and three - encryptions are used for each block of data; this uses 168 bits - of key (24 bytes in the TLS key generation method) and provides - the equivalent of 112 bits of security. [DES], [3DES] - - Digital Signature Standard (DSS) - A standard for digital signing, including the Digital Signing - Algorithm, approved by the National Institute of Standards and - Technology, defined in NIST FIPS PUB 186, "Digital Signature - Standard", published May, 1994 by the U.S. Dept. of Commerce. - [DSS] - - digital signatures - Digital signatures utilize public key cryptography and one-way - hash functions to produce a signature of the data that can be - authenticated, and is difficult to forge or repudiate. - - handshake - An initial negotiation between client and server that establishes - the parameters of their transactions. - - Initialization Vector (IV) - When a block cipher is used in CBC mode, the initialization - - - -Dierks & Rescorla Standards Track [Page 70] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - vector is exclusive-ORed with the first plaintext block prior to - encryption. - - IDEA - A 64-bit block cipher designed by Xuejia Lai and James Massey. - [IDEA] - - Message Authentication Code (MAC) - A Message Authentication Code is a one-way hash computed from a - message and some secret data. It is difficult to forge without - knowing the secret data. Its purpose is to detect if the message - has been altered. - - master secret - Secure secret data used for generating encryption keys, MAC - secrets, and IVs. - - MD5 - MD5 is a secure hashing function that converts an arbitrarily - long data stream into a digest of fixed size (16 bytes). [MD5] - - public key cryptography - A class of cryptographic techniques employing two-key ciphers. - Messages encrypted with the public key can only be decrypted with - the associated private key. Conversely, messages signed with the - private key can be verified with the public key. - - one-way hash function - A one-way transformation that converts an arbitrary amount of - data into a fixed-length hash. It is computationally hard to - reverse the transformation or to find collisions. MD5 and SHA are - examples of one-way hash functions. - - RC2 - A block cipher developed by Ron Rivest at RSA Data Security, Inc. - [RSADSI] described in [RC2]. - - RC4 - A stream cipher invented by Ron Rivest. A compatible cipher is - described in [SCH]. - - RSA - A very widely used public-key algorithm that can be used for - either encryption or digital signing. [RSA] - - server - The server is the application entity that responds to requests - for connections from clients. See also under client. - - - -Dierks & Rescorla Standards Track [Page 71] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - session - A TLS session is an association between a client and a server. - Sessions are created by the handshake protocol. Sessions define a - set of cryptographic security parameters that can be shared among - multiple connections. Sessions are used to avoid the expensive - negotiation of new security parameters for each connection. - - session identifier - A session identifier is a value generated by a server that - identifies a particular session. - - server write key - The key used to encrypt data written by the server. - - server write MAC secret - The secret data used to authenticate data written by the server. - - SHA - The Secure Hash Algorithm is defined in FIPS PUB 180-2. It - produces a 20-byte output. Note that all references to SHA - actually use the modified SHA-1 algorithm. [SHA] - - SSL - Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on - SSL Version 3.0 - - stream cipher - An encryption algorithm that converts a key into a - cryptographically strong keystream, which is then exclusive-ORed - with the plaintext. - - symmetric cipher - See bulk cipher. - - Transport Layer Security (TLS) - This protocol; also, the Transport Layer Security working group - of the Internet Engineering Task Force (IETF). See "Comments" at - the end of this document. - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 72] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix C. CipherSuite Definitions - -CipherSuite Key Cipher Hash - Exchange - -TLS_NULL_WITH_NULL_NULL NULL NULL NULL -TLS_RSA_WITH_NULL_MD5 RSA NULL MD5 -TLS_RSA_WITH_NULL_SHA RSA NULL SHA -TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5 -TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA -TLS_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA -TLS_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA -TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA -TLS_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA -TLS_RSA_WITH_AES_256_SHA RSA AES_256_CBC SHA -TLS_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA -TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA -TLS_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA -TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA -TLS_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA -TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA -TLS_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA -TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA -TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5 -TLS_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA -TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA -TLS_DH_DSS_WITH_AES_128_CBC_SHA DH_DSS AES_128_CBC SHA -TLS_DH_RSA_WITH_AES_128_CBC_SHA DH_RSA AES_128_CBC SHA -TLS_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS AES_128_CBC SHA -TLS_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA AES_128_CBC SHA -TLS_DH_anon_WITH_AES_128_CBC_SHA DH_anon AES_128_CBC SHA -TLS_DH_DSS_WITH_AES_256_CBC_SHA DH_DSS AES_256_CBC SHA -TLS_DH_RSA_WITH_AES_256_CBC_SHA DH_RSA AES_256_CBC SHA -TLS_DHE_DSS_WITH_AES_256_CBC_SHA DHE_DSS AES_256_CBC SHA -TLS_DHE_RSA_WITH_AES_256_CBC_SHA DHE_RSA AES_256_CBC SHA -TLS_DH_anon_WITH_AES_256_CBC_SHA DH_anon AES_256_CBC SHA - - Key - Exchange - Algorithm Description Key size limit - - DHE_DSS Ephemeral DH with DSS signatures None - DHE_RSA Ephemeral DH with RSA signatures None - DH_anon Anonymous DH, no signatures None - DH_DSS DH with DSS-based certificates None - DH_RSA DH with RSA-based certificates None - RSA = none - NULL No key exchange N/A - - - -Dierks & Rescorla Standards Track [Page 73] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - RSA RSA key exchange None - - Key Expanded IV Block - Cipher Type Material Key Material Size Size - - NULL Stream 0 0 0 N/A - IDEA_CBC Block 16 16 8 8 - RC2_CBC_40 Block 5 16 8 8 - RC4_40 Stream 5 16 0 N/A - RC4_128 Stream 16 16 0 N/A - DES40_CBC Block 5 8 8 8 - DES_CBC Block 8 8 8 8 - 3DES_EDE_CBC Block 24 24 8 8 - - Type - Indicates whether this is a stream cipher or a block cipher - running in CBC mode. - - Key Material - The number of bytes from the key_block that are used for - generating the write keys. - - Expanded Key Material - The number of bytes actually fed into the encryption algorithm. - - IV Size - The amount of data needed to be generated for the initialization - vector. Zero for stream ciphers; equal to the block size for - block ciphers. - - Block Size - The amount of data a block cipher enciphers in one chunk; a - block cipher running in CBC mode can only encrypt an even - multiple of its block size. - - Hash Hash Padding - function Size Size - NULL 0 0 - MD5 16 48 - SHA 20 40 - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 74] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix D. Implementation Notes - - The TLS protocol cannot prevent many common security mistakes. This - section provides several recommendations to assist implementors. - -D.1 Random Number Generation and Seeding - - TLS requires a cryptographically secure pseudorandom number generator - (PRNG). Care must be taken in designing and seeding PRNGs. PRNGs - based on secure hash operations, most notably MD5 and/or SHA, are - acceptable, but cannot provide more security than the size of the - random number generator state. (For example, MD5-based PRNGs usually - provide 128 bits of state.) - - To estimate the amount of seed material being produced, add the - number of bits of unpredictable information in each seed byte. For - example, keystroke timing values taken from a PC compatible's 18.2 Hz - timer provide 1 or 2 secure bits each, even though the total size of - the counter value is 16 bits or more. Seeding a 128-bit PRNG, one - would thus require approximately 100 such timer values. - - [RANDOM] provides guidance on the generation of random values. - -D.2 Certificates and Authentication - - Implementations are responsible for verifying the integrity of - certificates and should generally support certificate revocation - messages. Certificates should always be verified to ensure proper - signing by a trusted Certificate Authority (CA). The selection and - addition of trusted CAs should be done very carefully. Users should - be able to view information about the certificate and root CA. - -D.3 CipherSuites - - TLS supports a range of key sizes and security levels, including some - that provide no or minimal security. A proper implementation will - probably not support many cipher suites. For instance, anonymous - Diffie-Hellman is strongly discouraged because it cannot prevent man- - in-the-middle attacks. Applications should also enforce minimum and - maximum key sizes. For example, certificate chains containing 512-bit - RSA keys or signatures are not appropriate for high-security - applications. - - - - - - - - - -Dierks & Rescorla Standards Track [Page 75] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix E. Backward Compatibility - -E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0 - - Since there are various versions of TLS (1.0, 1.1, 1.2, and any - future versions) and SSL (2.0 and 3.0), means are needed to negotiate - the specific protocol version to use. The TLS protocol provides a - built-in mechanism for version negotiation so as not to bother other - protocol components with the complexities of version selection. - - TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use - compatible ClientHello messages; thus, supporting all of them is - relatively easy. Similarly, servers can easily handle clients trying - to use future versions of TLS as long as the ClientHello format - remains compatible, and the client support the highest protocol - version available in the server. - - A TLS 1.2 client who wishes to negotiate with such older servers will - send a normal TLS 1.2 ClientHello, containing { 3, 3 } (TLS 1.2) in - ClientHello.client_version. If the server does not support this - version, it will respond with ServerHello containing an older version - number. If the client agrees to use this version, the negotiation - will proceed as appropriate for the negotiated protocol. - - If the version chosen by the server is not supported by the client - (or not acceptable), the client MUST send a "protocol_version" alert - message and close the connection. - - If a TLS server receives a ClientHello containing a version number - greater than the highest version supported by the server, it MUST - reply according to the highest version supported by the server. - - A TLS server can also receive a ClientHello containing version number - smaller than the highest supported version. If the server wishes to - negotiate with old clients, it will proceed as appropriate for the - highest version supported by the server that is not greater than - ClientHello.client_version. For example, if the server supports TLS - 1.0, 1.1, and 1.2, and client_version is TLS 1.0, the server will - proceed with a TLS 1.0 ServerHello. If server supports (or is willing - to use) only versions greater than client_version, it MUST send a - "protocol_version" alert message and close the connection. - - Whenever a client already knows the highest protocol known to a - server (for example, when resuming a session), it SHOULD initiate the - connection in that native protocol. - - Note: some server implementations are known to implement version - negotiation incorrectly. For example, there are buggy TLS 1.0 servers - - - -Dierks & Rescorla Standards Track [Page 76] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - that simply close the connection when the client offers a version - newer than TLS 1.0. Also, it is known that some servers will refuse - connection if any TLS extensions are included in ClientHello. - Interoperability with such buggy servers is a complex topic beyond - the scope of this document, and may require multiple connection - attempts by the client. - - Earlier versions of the TLS specification were not fully clear on - what the record layer version number (TLSPlaintext.version) should - contain when sending ClientHello (i.e., before it is known which - version of the protocol will be employed). Thus, TLS servers - compliant with this specification MUST accept any value {03,XX} as - the record layer version number for ClientHello. - - TLS clients that wish to negotiate with older servers MAY send any - value {03,XX} as the record layer version number. Typical values - would be {03,00}, the lowest version number supported by the client, - and the value of ClientHello.client_version. No single value will - guarantee interoperability with all old servers, but this is a - complex topic beyond the scope of this document. - -E.2 Compatibility with SSL 2.0 - - TLS 1.2 clients that wish to support SSL 2.0 servers MUST send - version 2.0 CLIENT-HELLO messages defined in [SSL2]. The message MUST - contain the same version number as would be used for ordinary - ClientHello, and MUST encode the supported TLS ciphersuites in the - CIPHER-SPECS-DATA field as described below. - -Warning: The ability to send version 2.0 CLIENT-HELLO messages will be - phased out with all due haste, since the newer ClientHello format - provides better mechanisms for moving to newer versions and - negotiating extensions. TLS 1.2 clients SHOULD NOT support SSL 2.0. - - However, even TLS servers that do not support SSL 2.0 SHOULD accept - version 2.0 CLIENT-HELLO messages. The message is presented below in - sufficient detail for TLS server implementors; the true definition is - still assumed to be [SSL2]. - - For negotiation purposes, 2.0 CLIENT-HELLO is interpreted the same - way as a ClientHello with a "null" compression method and no - extensions. Note that this message MUST be sent directly on the wire, - not wrapped as a TLS record. For the purposes of calculating Finished - and CertificateVerify, the msg_length field is not considered to be a - part of the handshake message. - - uint8 V2CipherSpec[3]; - - - - -Dierks & Rescorla Standards Track [Page 77] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - struct { - uint16 msg_length; - uint8 msg_type; - Version version; - uint16 cipher_spec_length; - uint16 session_id_length; - uint16 challenge_length; - V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length]; - opaque session_id[V2ClientHello.session_id_length]; - opaque challenge[V2ClientHello.challenge_length; - } V2ClientHello; - - msg_length - The highest bit MUST be 1; the remaining bits contain the - length of the following data in bytes. - - msg_type - This field, in conjunction with the version field, identifies a - version 2 client hello message. The value SHOULD be one (1). - - version - Equal to ClientHello.client_version. - - cipher_spec_length - This field is the total length of the field cipher_specs. It - cannot be zero and MUST be a multiple of the V2CipherSpec length - (3). - - session_id_length - This field MUST have a value of zero. MUST be zero for a client - that claims to support TLS 1.2. - - challenge_length - The length in bytes of the client's challenge to the server to - authenticate itself. Historically, permissible values are between - 16 and 32 bytes inclusive. When using the SSLv2 backward - compatible handshake the client MUST use a 32-byte challenge. - - cipher_specs - This is a list of all CipherSpecs the client is willing and able - to use. In addition to the 2.0 cipher specs defined in [SSL2], - this includes the TLS cipher suites normally sent in - ClientHello.cipher_suites, each cipher suite prefixed by a zero - byte. For example, TLS ciphersuite {0x00,0x0A} would be sent as - {0x00,0x00,0x0A}. - - session_id - This field MUST be empty. - - - -Dierks & Rescorla Standards Track [Page 78] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - challenge - Corresponds to ClientHello.random. If the challenge length is - less than 32, the TLS server will pad the data with leading - (note: not trailing) zero bytes to make it 32 bytes long. - - Note: Requests to resume a TLS session MUST use a TLS client hello. - -E.2. Avoiding Man-in-the-Middle Version Rollback - - When TLS clients fall back to Version 2.0 compatibility mode, they - SHOULD use special PKCS #1 block formatting. This is done so that TLS - servers will reject Version 2.0 sessions with TLS-capable clients. - - When TLS clients are in Version 2.0 compatibility mode, they set the - right-hand (least-significant) 8 random bytes of the PKCS padding - (not including the terminal null of the padding) for the RSA - encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY - to 0x03 (the other padding bytes are random). After decrypting the - ENCRYPTED-KEY-DATA field, servers that support TLS SHOULD issue an - error if these eight padding bytes are 0x03. Version 2.0 servers - receiving blocks padded in this manner will proceed normally. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 79] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Appendix F. Security Analysis - - The TLS protocol is designed to establish a secure connection between - a client and a server communicating over an insecure channel. This - document makes several traditional assumptions, including that - attackers have substantial computational resources and cannot obtain - secret information from sources outside the protocol. Attackers are - assumed to have the ability to capture, modify, delete, replay, and - otherwise tamper with messages sent over the communication channel. - This appendix outlines how TLS has been designed to resist a variety - of attacks. - -F.1. Handshake Protocol - - The handshake protocol is responsible for selecting a CipherSpec and - generating a Master Secret, which together comprise the primary - cryptographic parameters associated with a secure session. The - handshake protocol can also optionally authenticate parties who have - certificates signed by a trusted certificate authority. - -F.1.1. Authentication and Key Exchange - - TLS supports three authentication modes: authentication of both - parties, server authentication with an unauthenticated client, and - total anonymity. Whenever the server is authenticated, the channel is - secure against man-in-the-middle attacks, but completely anonymous - sessions are inherently vulnerable to such attacks. Anonymous - servers cannot authenticate clients. If the server is authenticated, - its certificate message must provide a valid certificate chain - leading to an acceptable certificate authority. Similarly, - authenticated clients must supply an acceptable certificate to the - server. Each party is responsible for verifying that the other's - certificate is valid and has not expired or been revoked. - - The general goal of the key exchange process is to create a - pre_master_secret known to the communicating parties and not to - attackers. The pre_master_secret will be used to generate the - master_secret (see Section 8.1). The master_secret is required to - generate the finished messages, encryption keys, and MAC secrets (see - Sections 7.4.9 and 6.3). By sending a correct finished message, - parties thus prove that they know the correct pre_master_secret. - -F.1.1.1. Anonymous Key Exchange - - Completely anonymous sessions can be established using RSA or Diffie- - Hellman for key exchange. With anonymous RSA, the client encrypts a - pre_master_secret with the server's uncertified public key extracted - from the server key exchange message. The result is sent in a client - - - -Dierks & Rescorla Standards Track [Page 80] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - key exchange message. Since eavesdroppers do not know the server's - private key, it will be infeasible for them to decode the - pre_master_secret. - - Note: No anonymous RSA Cipher Suites are defined in this document. - - With Diffie-Hellman, the server's public parameters are contained in - the server key exchange message and the client's are sent in the - client key exchange message. Eavesdroppers who do not know the - private values should not be able to find the Diffie-Hellman result - (i.e. the pre_master_secret). - - Warning: Completely anonymous connections only provide protection - against passive eavesdropping. Unless an independent tamper- - proof channel is used to verify that the finished messages - were not replaced by an attacker, server authentication is - required in environments where active man-in-the-middle - attacks are a concern. - -F.1.1.2. RSA Key Exchange and Authentication - - With RSA, key exchange and server authentication are combined. The - public key is contained in the server's certificate. Note that - compromise of the server's static RSA key results in a loss of - confidentiality for all sessions protected under that static key. TLS - users desiring Perfect Forward Secrecy should use DHE cipher suites. - The damage done by exposure of a private key can be limited by - changing one's private key (and certificate) frequently. - - After verifying the server's certificate, the client encrypts a - pre_master_secret with the server's public key. By successfully - decoding the pre_master_secret and producing a correct finished - message, the server demonstrates that it knows the private key - corresponding to the server certificate. - - When RSA is used for key exchange, clients are authenticated using - the certificate verify message (see Section 7.4.9). The client signs - a value derived from the master_secret and all preceding handshake - messages. These handshake messages include the server certificate, - which binds the signature to the server, and ServerHello.random, - which binds the signature to the current handshake process. - -F.1.1.3. Diffie-Hellman Key Exchange with Authentication - - When Diffie-Hellman key exchange is used, the server can either - supply a certificate containing fixed Diffie-Hellman parameters or - use the server key exchange message to send a set of temporary - Diffie-Hellman parameters signed with a DSS or RSA certificate. - - - -Dierks & Rescorla Standards Track [Page 81] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Temporary parameters are hashed with the hello.random values before - signing to ensure that attackers do not replay old parameters. In - either case, the client can verify the certificate or signature to - ensure that the parameters belong to the server. - - If the client has a certificate containing fixed Diffie-Hellman - parameters, its certificate contains the information required to - complete the key exchange. Note that in this case the client and - server will generate the same Diffie-Hellman result (i.e., - pre_master_secret) every time they communicate. To prevent the - pre_master_secret from staying in memory any longer than necessary, - it should be converted into the master_secret as soon as possible. - Client Diffie-Hellman parameters must be compatible with those - supplied by the server for the key exchange to work. - - If the client has a standard DSS or RSA certificate or is - unauthenticated, it sends a set of temporary parameters to the server - in the client key exchange message, then optionally uses a - certificate verify message to authenticate itself. - - If the same DH keypair is to be used for multiple handshakes, either - because the client or server has a certificate containing a fixed DH - keypair or because the server is reusing DH keys, care must be taken - to prevent small subgroup attacks. Implementations SHOULD follow the - guidelines found in [SUBGROUP]. - - Small subgroup attacks are most easily avoided by using one of the - DHE ciphersuites and generating a fresh DH private key (X) for each - handshake. If a suitable base (such as 2) is chosen, g^X mod p can be - computed very quickly, therefore the performance cost is minimized. - Additionally, using a fresh key for each handshake provides Perfect - Forward Secrecy. Implementations SHOULD generate a new X for each - handshake when using DHE ciphersuites. - -F.1.2. Version Rollback Attacks - - Because TLS includes substantial improvements over SSL Version 2.0, - attackers may try to make TLS-capable clients and servers fall back - to Version 2.0. This attack can occur if (and only if) two TLS- - capable parties use an SSL 2.0 handshake. - - Although the solution using non-random PKCS #1 block type 2 message - padding is inelegant, it provides a reasonably secure way for Version - 3.0 servers to detect the attack. This solution is not secure against - attackers who can brute force the key and substitute a new ENCRYPTED- - KEY-DATA message containing the same key (but with normal padding) - before the application specified wait threshold has expired. Altering - the padding of the least significant 8 bytes of the PKCS padding does - - - -Dierks & Rescorla Standards Track [Page 82] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - not impact security for the size of the signed hashes and RSA key - lengths used in the protocol, since this is essentially equivalent to - increasing the input block size by 8 bytes. - -F.1.3. Detecting Attacks Against the Handshake Protocol - - An attacker might try to influence the handshake exchange to make the - parties select different encryption algorithms than they would - normally chooses. - - For this attack, an attacker must actively change one or more - handshake messages. If this occurs, the client and server will - compute different values for the handshake message hashes. As a - result, the parties will not accept each others' finished messages. - Without the master_secret, the attacker cannot repair the finished - messages, so the attack will be discovered. - -F.1.4. Resuming Sessions - - When a connection is established by resuming a session, new - ClientHello.random and ServerHello.random values are hashed with the - session's master_secret. Provided that the master_secret has not been - compromised and that the secure hash operations used to produce the - encryption keys and MAC secrets are secure, the connection should be - secure and effectively independent from previous connections. - Attackers cannot use known encryption keys or MAC secrets to - compromise the master_secret without breaking the secure hash - operations (which use both SHA and MD5). - - Sessions cannot be resumed unless both the client and server agree. - If either party suspects that the session may have been compromised, - or that certificates may have expired or been revoked, it should - force a full handshake. An upper limit of 24 hours is suggested for - session ID lifetimes, since an attacker who obtains a master_secret - may be able to impersonate the compromised party until the - corresponding session ID is retired. Applications that may be run in - relatively insecure environments should not write session IDs to - stable storage. - -F.1.5 Extensions - - Security considerations for the extension mechanism in general, and - the design of new extensions, are described in the previous section. - A security analysis of each of the extensions defined in this - document is given below. - - In general, implementers should continue to monitor the state of the - art, and address any weaknesses identified. - - - -Dierks & Rescorla Standards Track [Page 83] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -F.2. Protecting Application Data - - The master_secret is hashed with the ClientHello.random and - ServerHello.random to produce unique data encryption keys and MAC - secrets for each connection. - - Outgoing data is protected with a MAC before transmission. To prevent - message replay or modification attacks, the MAC is computed from the - MAC secret, the sequence number, the message length, the message - contents, and two fixed character strings. The message type field is - necessary to ensure that messages intended for one TLS Record Layer - client are not redirected to another. The sequence number ensures - that attempts to delete or reorder messages will be detected. Since - sequence numbers are 64 bits long, they should never overflow. - Messages from one party cannot be inserted into the other's output, - since they use independent MAC secrets. Similarly, the server-write - and client-write keys are independent, so stream cipher keys are used - only once. - - If an attacker does break an encryption key, all messages encrypted - with it can be read. Similarly, compromise of a MAC key can make - message modification attacks possible. Because MACs are also - encrypted, message-alteration attacks generally require breaking the - encryption algorithm as well as the MAC. - - Note: MAC secrets may be larger than encryption keys, so messages can - remain tamper resistant even if encryption keys are broken. - -F.3. Explicit IVs - - [CBCATT] describes a chosen plaintext attack on TLS that depends - on knowing the IV for a record. Previous versions of TLS [TLS1.0] - used the CBC residue of the previous record as the IV and - therefore enabled this attack. This version uses an explicit IV - in order to protect against this attack. - -F.4. Security of Composite Cipher Modes - - TLS secures transmitted application data via the use of symmetric - encryption and authentication functions defined in the negotiated - ciphersuite. The objective is to protect both the integrity and - confidentiality of the transmitted data from malicious actions by - active attackers in the network. It turns out that the order in - which encryption and authentication functions are applied to the - data plays an important role for achieving this goal [ENCAUTH]. - - The most robust method, called encrypt-then-authenticate, first - applies encryption to the data and then applies a MAC to the - - - -Dierks & Rescorla Standards Track [Page 84] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - ciphertext. This method ensures that the integrity and - confidentiality goals are obtained with ANY pair of encryption - and MAC functions, provided that the former is secure against - chosen plaintext attacks and the MAC is secure against chosen- - message attacks. TLS uses another method, called authenticate- - then-encrypt, in which first a MAC is computed on the plaintext - and then the concatenation of plaintext and MAC is encrypted. - This method has been proven secure for CERTAIN combinations of - encryption functions and MAC functions, but is not guaranteed to - be secure in general. In particular, it has been shown that there - exist perfectly secure encryption functions (secure even in the - information-theoretic sense) that combined with any secure MAC - function, fail to provide the confidentiality goal against an - active attack. Therefore, new ciphersuites and operation modes - adopted into TLS need to be analyzed under the authenticate-then- - encrypt method to verify that they achieve the stated integrity - and confidentiality goals. - - Currently, the security of the authenticate-then-encrypt method - has been proven for some important cases. One is the case of - stream ciphers in which a computationally unpredictable pad of - the length of the message, plus the length of the MAC tag, is - produced using a pseudo-random generator and this pad is xor-ed - with the concatenation of plaintext and MAC tag. The other is - the case of CBC mode using a secure block cipher. In this case, - security can be shown if one applies one CBC encryption pass to - the concatenation of plaintext and MAC and uses a new, - independent, and unpredictable, IV for each new pair of plaintext - and MAC. In previous versions of SSL, CBC mode was used properly - EXCEPT that it used a predictable IV in the form of the last - block of the previous ciphertext. This made TLS open to chosen - plaintext attacks. This verson of the protocol is immune to - those attacks. For exact details in the encryption modes proven - secure see [ENCAUTH]. - -F.5 Denial of Service - - TLS is susceptible to a number of denial of service (DoS) attacks. - In particular, an attacker who initiates a large number of TCP - connections can cause a server to consume large amounts of CPU doing - RSA decryption. However, because TLS is generally used over TCP, it - is difficult for the attacker to hide his point of origin if proper - TCP SYN randomization is used [SEQNUM] by the TCP stack. - - Because TLS runs over TCP, it is also susceptible to a number of - denial of service attacks on individual connections. In particular, - attackers can forge RSTs, thereby terminating connections, or forge - partial TLS records, thereby causing the connection to stall. These - - - -Dierks & Rescorla Standards Track [Page 85] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - attacks cannot in general be defended against by a TCP-using - protocol. Implementors or users who are concerned with this class of - attack should use IPsec AH [AH] or ESP [ESP]. - -F.6. Final Notes - - For TLS to be able to provide a secure connection, both the client - and server systems, keys, and applications must be secure. In - addition, the implementation must be free of security errors. - - The system is only as strong as the weakest key exchange and - authentication algorithm supported, and only trustworthy - cryptographic functions should be used. Short public keys and - anonymous servers should be used with great caution. Implementations - and users must be careful when deciding which certificates and - certificate authorities are acceptable; a dishonest certificate - authority can do tremendous damage. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 86] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - -Security Considerations - - Security issues are discussed throughout this memo, especially in - Appendices D, E, and F. - - -Changes in This Version - - [RFC Editor: Please delete this] - - - Forbid decryption_failed [issue 5] - - - Fix CertHashTypes declaration [issue 20] - - - Fix client_version in 7.4.1.2 [issue 19] - - - Require Bleichenbacher and timing attack protection [issues 17 - and - 12]. - - - Merged RFC-editor changes back in. - - - Editorial changes from NIST [issue 8] - - - Clarified the meaning of HelloRequest [issue 39] - - - Editorial nits from Peter Williams [issue 35] - - - Made maximum fragment size a MUST [issue 9] - - - Clarified that resumption is not mandatory and servers may - refuse [issue 37] - - - Fixed identifier for cert_hash_types [issue 38] - - - Forbid sending unknown record types [issue 11] - - - Clarify that DH parameters and other integers are unsigned [issue - 28] - - - Clarify when a server Certificate is sent [isssue 29] - - - Prohibit zero-length fragments [issue 10] - - - Fix reference for DES/3DES [issue 18] - - - Clean up some notes on deprecated alerts [issue 6] - - - - -Dierks & Rescorla Standards Track [Page 87] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - - Remove ephemeral RSA [issue 3] - - - Stripped out discussion of how to generate the IV and replaced it - with a randomness/unpredictability requirement [issue 7] - - - Replaced the PKCS#1 text with references to PKCS#1 v2. This also - includes DigestInfo encoding [issues 1 and 22] - - - Removed extension definitions and merged the ExtendedHello - definitions [issues 31 and 32] - - - Replaced CipherSpec references with SecurityParameters references - [issue 2] - - - Cleaned up IANA text [issues 33 and 34] - - - Cleaned up backward compatibility text [issue 25] - -Normative References - [AES] National Institute of Standards and Technology, - "Specification for the Advanced Encryption Standard (AES)" - FIPS 197. November 26, 2001. - - [3DES] National Institute of Standards and Tecnology, - "Recommendation for the Triple Data Encryption Algorithm - (TDEA) Block Cipher", NIST Special Publication 800-67, May - 2004. - - [DES] National Institute of Standards and Technology, "Data - Encryption Standard (DES)", FIPS PUB 46-3, October 1999. - - [DSS] NIST FIPS PUB 186-2, "Digital Signature Standard," National - Institute of Standards and Technology, U.S. Department of - Commerce, 2000. - - - [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- - Hashing for Message Authentication", RFC 2104, February - 1997. - - [HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, - L., Leach, P. and T. Berners-Lee, "Hypertext Transfer - Protocol -- HTTP/1.1", RFC 2616, June 1999. - - [IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH - Series in Information Processing, v. 1, Konstanz: Hartung- - Gorre Verlag, 1992. - - - - -Dierks & Rescorla Standards Track [Page 88] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - [IDNA] Faltstrom, P., Hoffman, P. and A. Costello, - "Internationalizing Domain Names in Applications (IDNA)", - RFC 3490, March 2003. - - [MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, - April 1992. - - [OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. - Adams, "Internet X.509 Public Key Infrastructure: Online - Certificate Status Protocol - OCSP", RFC 2560, June 1999. - - [PKCS1B] J. Jonsson, B. Kaliski, "Public-Key Cryptography Standards - (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC - 3447, February 2003. - - [PKIOP] Housley, R. and P. Hoffman, "Internet X.509 Public Key - Infrastructure - Operation Protocols: FTP and HTTP", RFC - 2585, May 1999. - - - [PKIX] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet - Public Key Infrastructure: Part I: X.509 Certificate and CRL - Profile", RFC 3280, April 2002. - - [RC2] Rivest, R., "A Description of the RC2(r) Encryption - Algorithm", RFC 2268, March 1998. - - [SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms, - and Source Code in C, 2ed", Published by John Wiley & Sons, - Inc. 1996. - - [SHA] NIST FIPS PUB 180-2, "Secure Hash Standard," National - Institute of Standards and Technology, U.S. Department of - Commerce., August 2001. - - [REQ] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. - - [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an - IANA Considerations Section in RFCs", BCP 25, RFC 2434, - October 1998. - - [TLSAES] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites - for Transport Layer Security (TLS)", RFC 3268, June 2002. - - [TLSEXT] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., - Wright, T., "Transport Layer Security (TLS) Extensions", RFC - 3546, June 2003. - - - -Dierks & Rescorla Standards Track [Page 89] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - [TLSKRB] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher - Suites to Transport Layer Security (TLS)", RFC 2712, October - 1999. - - [URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform - Resource Identifiers (URI): Generic Syntax", RFC 2396, - August 1998. - - [UTF8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", - RFC 3629, November 2003. - - [X509-4th] ITU-T Recommendation X.509 (2000) | ISO/IEC 9594- 8:2001, - "Information Systems - Open Systems Interconnection - The - Directory: Public key and Attribute certificate - frameworks." - - [X509-4th-TC1] ITU-T Recommendation X.509(2000) Corrigendum 1(2001) | - ISO/IEC 9594-8:2001/Cor.1:2002, Technical Corrigendum 1 to - ISO/IEC 9594:8:2001. - -Informative References - - [AEAD] Mcgrew, D., "Authenticated Encryption", July 2006, draft- - mcgrew-auth-enc-00.txt. - - [AH] Kent, S., and Atkinson, R., "IP Authentication Header", RFC - 4302, December 2005. - - [BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against - Protocols Based on RSA Encryption Standard PKCS #1" in - Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, pages: - 1-12, 1998. - - [CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS: - Problems and Countermeasures", - http://www.openssl.org/~bodo/tls-cbc.txt. - - [CBCTIME] Canvel, B., "Password Interception in a SSL/TLS Channel", - http://lasecwww.epfl.ch/memo_ssl.shtml, 2003. - - [CCM] "NIST Special Publication 800-38C: The CCM Mode for - Authentication and Confidentiality", - http://csrc.nist.gov/publications/nistpubs/SP800-38C.pdf. - - [ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication - for Protecting Communications (Or: How Secure is SSL?)", - Crypto 2001. - - - - -Dierks & Rescorla Standards Track [Page 90] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - [ESP] Kent, S., and Atkinson, R., "IP Encapsulating Security - Payload (ESP)", RFC 4303, December 2005. - - [GCM] "NIST Special Publication 800-38C: The CCM Mode for - Authentication and Confidentiality", - http://csrc.nist.gov/publications/nistpubs/SP800-38C.pdf. - - [KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based - Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/, - March 2003. - - [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax - Standard," version 1.5, November 1993. - - [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax - Standard," version 1.5, November 1993. - - [RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness - Requirements for Security", BCP 106, RFC 4086, June 2005. - - [RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for - Obtaining Digital Signatures and Public-Key Cryptosystems," - Communications of the ACM, v. 21, n. 2, Feb 1978, pp. - 120-126. - - [SEQNUM] Bellovin. S., "Defending Against Sequence Number Attacks", - RFC 1948, May 1996. - - [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications - Corp., Feb 9, 1995. - - [SSL3] A. Frier, P. Karlton, and P. Kocher, "The SSL 3.0 Protocol", - Netscape Communications Corp., Nov 18, 1996. - - [SUBGROUP] Zuccherato, R., "Methods for Avoiding the "Small-Subgroup" - Attacks on the Diffie-Hellman Key Agreement Method for - S/MIME", RFC 2785, March 2000. - - [TCP] Postel, J., "Transmission Control Protocol," STD 7, RFC 793, - September 1981. - - [TIMING] Boneh, D., Brumley, D., "Remote timing attacks are - practical", USENIX Security Symposium 2003. - - [TLS1.0] Dierks, T., and C. Allen, "The TLS Protocol, Version 1.0", - RFC 2246, January 1999. - - [TLS1.1] Dierks, T., and E. Rescorla, "The TLS Protocol, Version - - - -Dierks & Rescorla Standards Track [Page 91] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - 1.1", RFC 4346, April, 2006. - - [X501] ITU-T Recommendation X.501: Information Technology - Open - Systems Interconnection - The Directory: Models, 1993. - - [X509] ITU-T Recommendation X.509 (1997 E): Information Technology - - Open Systems Interconnection - "The Directory - - Authentication Framework". 1988. - - [XDR] Srinivansan, R., Sun Microsystems, "XDR: External Data - Representation Standard", RFC 1832, August 1995. - - -Credits - - Working Group Chairs - Eric Rescorla - EMail: ekr@networkresonance.com - - Pasi Eronen - pasi.eronen@nokia.com - - - Editors - - Tim Dierks Eric Rescorla - Independent Network Resonance, Inc. - - EMail: tim@dierks.org EMail: ekr@networkresonance.com - - - - Other contributors - - Christopher Allen (co-editor of TLS 1.0) - Alacrity Ventures - ChristopherA@AlacrityManagement.com - - Martin Abadi - University of California, Santa Cruz - abadi@cs.ucsc.edu - - Steven M. Bellovin - Columbia University - smb@cs.columbia.edu - - Simon Blake-Wilson - BCI - - - -Dierks & Rescorla Standards Track [Page 92] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - EMail: sblakewilson@bcisse.com - - Ran Canetti - IBM - canetti@watson.ibm.com - - Pete Chown - Skygate Technology Ltd - pc@skygate.co.uk - - Taher Elgamal - taher@securify.com - Securify - - Anil Gangolli - anil@busybuddha.org - - Kipp Hickman - - David Hopwood - Independent Consultant - EMail: david.hopwood@blueyonder.co.uk - - Phil Karlton (co-author of SSLv3) - - Paul Kocher (co-author of SSLv3) - Cryptography Research - paul@cryptography.com - - Hugo Krawczyk - Technion Israel Institute of Technology - hugo@ee.technion.ac.il - - Jan Mikkelsen - Transactionware - EMail: janm@transactionware.com - - Magnus Nystrom - RSA Security - EMail: magnus@rsasecurity.com - - Robert Relyea - Netscape Communications - relyea@netscape.com - - Jim Roskind - Netscape Communications - jar@netscape.com - - - -Dierks & Rescorla Standards Track [Page 93] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Michael Sabin - - Dan Simon - Microsoft, Inc. - dansimon@microsoft.com - - Tom Weinstein - - Tim Wright - Vodafone - EMail: timothy.wright@vodafone.com - -Comments - - The discussion list for the IETF TLS working group is located at the - e-mail address <tls@ietf.org>. Information on the group and - information on how to subscribe to the list is at - <https://www1.ietf.org/mailman/listinfo/tls> - - Archives of the list can be found at: - <http://www.ietf.org/mail-archive/web/tls/current/index.html> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Dierks & Rescorla Standards Track [Page 94] draft-ietf-tls-rfc4346-bis-03.txt TLS March 2007 - - - Full Copyright Statement - - Copyright (C) The IETF Trust (2007). - - This document is subject to the rights, licenses and restrictions - contained in BCP 78, and except as set forth therein, the authors - retain all their rights. - - This document and the information contained herein are provided on an - "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS - OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND - THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS - OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF - THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED - WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - - - Intellectual Property - - The IETF takes no position regarding the validity or scope of any - Intellectual Property Rights or other rights that might be claimed to - pertain to the implementation or use of the technology described in - this document or the extent to which any license under such rights - might or might not be available; nor does it represent that it has - made any independent effort to identify any such rights. 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