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-
-
-
-
-
-
- Tim Dierks
- Independent
- Eric Rescorla
-INTERNET-DRAFT RTFM, Inc.
-<draft-ietf-tls-rfc2246-bis-13.txt> June 2005 (Expires December 2005)
-
- The TLS Protocol
- Version 1.1
-
-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 a "work in progress."
-
-The list of current Internet-Drafts can be accessed at
-http://www.ietf.org/1id-abstracts.html
-
-The list of Internet-Draft Shadow Directories can be accessed at
-http://www.ietf.org/shadow.html
-
-Copyright Notice
-
- Copyright (C) The Internet Society (2005). All Rights Reserved.
-
-Abstract
-
- This document specifies Version 1.1 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
- 5 1.1 Differences from TLS 1.0
-
-
-
-Dierks & Rescorla Standards Track [Page 1] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- 6 1.1 Requirements Terminology
- 7 2. Goals
- 7 3. Goals of this document
- 7 4. Presentation language
- 8 4.1. Basic block size
- 9 4.2. Miscellaneous
- 9 4.3. Vectors
- 9 4.4. Numbers
- 10 4.5. Enumerateds
- 10 4.6. Constructed types
- 11 4.6.1. Variants
- 12 4.7. Cryptographic attributes
- 13 4.8. Constants
- 14 5. HMAC and the pseudorandom function
- 14 6. The TLS Record Protocol
- 17 6.1. Connection states
- 18 6.2. Record layer
- 20 6.2.1. Fragmentation
- 20 6.2.2. Record compression and decompression
- 21 6.2.3. Record payload protection
- 22 6.2.3.1. Null or standard stream cipher
- 23 6.2.3.2. CBC block cipher
- 23 6.3. Key calculation
- 26 7. The TLS Handshaking Protocols
- 27 7.1. Change cipher spec protocol
- 28 7.2. Alert protocol
- 28 7.2.1. Closure alerts
- 29 7.2.2. Error alerts
- 30 7.3. Handshake Protocol overview
- 33 7.4. Handshake protocol
- 37 7.4.1. Hello messages
- 38 7.4.1.1. Hello request
- 38 7.4.1.2. Client hello
- 39 7.4.1.3. Server hello
- 41 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
- 48 7.4.6. Client certificate
- 48 7.4.7. Client key exchange message
- 48 7.4.7.1. RSA encrypted premaster secret message
- 49 7.4.7.2. 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 8.1.1. RSA
- 55 8.1.2. Diffie-Hellman
-
-
-
-Dierks & Rescorla Standards Track [Page 2] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- 55 9. Mandatory Cipher Suites
- 55 A. Protocol constant values
- 57 A.1. Record layer
- 57 A.2. Change cipher specs message
- 58 A.3. Alert messages
- 58 A.4. Handshake protocol
- 59 A.4.1. Hello messages
- 59 A.4.2. Server authentication and key exchange messages
- 60 A.4.3. Client authentication and key exchange messages
- 61 A.4.4. Handshake finalization message
- 62 A.5. The CipherSuite
- 62 A.6. The Security Parameters
- 65 B. Glossary
- 67 C. CipherSuite definitions
- 71 D. Implementation Notes
- 73 D.1 Random Number Generation and Seeding
- 73 D.2 Certificates and authentication
- 73 D.3 CipherSuites
- 73 E. Backward Compatibility With SSL
- 74 E.1. Version 2 client hello
- 75 E.2. Avoiding man-in-the-middle version rollback
- 76 F. Security analysis
- 78 F.1. Handshake protocol
- 78 F.1.1. Authentication and key exchange
- 78 F.1.1.1. Anonymous key exchange
- 78 F.1.1.2. RSA key exchange and authentication
- 79 F.1.1.3. Diffie-Hellman key exchange with authentication
- 80 F.1.2. Version rollback attacks
- 80 F.1.3. Detecting attacks against the handshake protocol
- 81 F.1.4. Resuming sessions
- 81 F.1.5. MD5 and SHA
- 82 F.2. Protecting application data
- 82 F.3. Explicit IVs
- 82 F.4 Security of Composite Cipher Modes
- 83 F.5 Denial of Service
- 84 F.6. Final notes
- 84
-
-
-Change history
-
- 22-Jun-05 ekr@rtfm.com
- * IESG comments
- * IANA comments
- * Cleaned up some references
-
- 31-May-05 ekr@rtfm.com
- * IETF Last Call comments (minor cleanups)
-
-
-
-Dierks & Rescorla Standards Track [Page 3] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- 03-Dec-04 ekr@rtfm.com
- * Removed export cipher suites
-
- 26-Oct-04 ekr@rtfm.com
- * Numerous cleanups from Last Call comments
-
- 10-Aug-04 ekr@rtfm.com
- * Added clarifying material about interleaved application data.
-
- 27-Jul-04 ekr@rtfm.com
- * Premature closes no longer cause a session to be nonresumable.
- Response to WG consensus.
-
- * Added IANA considerations and registry for cipher suites
- and ClientCertificateTypes
-
- 26-Jun-03 ekr@rtfm.com
- * Incorporated Last Call comments from Franke Marcus, Jack Lloyd,
- Brad Wetmore, and others.
-
- 22-Apr-03 ekr@rtfm.com
- * coverage of the Vaudenay, Boneh-Brumley, and KPR attacks
- * cleaned up IV text a bit.
- * Added discussion of Denial of Service attacks.
-
- 11-Feb-02 ekr@rtfm.com
- * Clarified the behavior of empty certificate lists [Nelson Bolyard]
- * Added text explaining the security implications of authenticate
- then encrypt.
- * Cleaned up the explicit IV text.
- * Added some more acknowledgement names
-
- 02-Nov-02 ekr@rtfm.com
- * Changed this to be TLS 1.1.
- * Added fixes for the Rogaway and Vaudenay CBC attacks
- * Separated references into normative and informative
-
- 01-Mar-02 ekr@rtfm.com
- * Tightened up the language in F.1.1.2 [Peter Watkins]
- * Fixed smart quotes [Bodo Moeller]
- * Changed handling of padding errors to prevent CBC-based attack
- [Bodo Moeller]
- * Fixed certificate_list spec in the appendix [Aman Sawrup]
- * Fixed a bug in the V2 definitions [Aman Sawrup]
- * Fixed S 7.2.1 to point out that you don't need a close notify
- if you just sent some other fatal alert [Andreas Sterbenz]
- * Marked alert 41 reserved [Andreas Sterbenz]
- * Changed S 7.4.2 to point out that 512-bit keys cannot be used for
-
-
-
-Dierks & Rescorla Standards Track [Page 4] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- signing [Andreas Sterbenz]
- * Added reserved client key types from SSLv3 [Andreas Sterbenz]
- * Changed EXPORT40 to "40-bit EXPORT" in S 9 [Andreas Sterbenz]
- * Removed RSA patent statement [Andreas Sterbenz]
- * Removed references to BSAFE and RSAREF [Andreas Sterbenz]
-
- 14-Feb-02 ekr@rtfm.com
- * Re-converted to I-D from RFC
- * Made RSA/3DES the mandatory cipher suite.
- * Added discussion of the EncryptedPMS encoding and PMS version number
- issues to 7.4.7.1
- * Removed the requirement in 7.4.1.3 that the Server random must be
- different from the Client random, since these are randomly generated
- and we don't expect servers to reject Server random values which
- coincidentally are the same as the Client random.
- * Replaced may/should/must with MAY/SHOULD/MUST where appropriate.
- In many cases, shoulds became MUSTs, where I believed that was the
- actual sense of the text. Added an RFC 2119 bulletin.
- * Clarified the meaning of "empty certificate" message. [Peter Gutmann]
- * Redid the CertificateRequest grammar to allow no distinguished names.
- [Peter Gutmann]
- * Removed the reference to requiring the master secret to generate
- the CertificateVerify in F.1.1 [Bodo Moeller]
- * Deprecated EXPORT40.
- * Fixed a bunch of errors in the SSLv2 backward compatible client hello.
-
-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
- 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
-
-
-
-Dierks & Rescorla Standards Track [Page 5] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- 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 up to the judgment of the designers and
- implementors of protocols which run on top of TLS.
-
-1.1 Differences from TLS 1.0
- This document is a revision of the TLS 1.0 [TLS1.0] protocol which
- contains some small security improvements, clarifications, and
- editorial improvements. The major changes are:
-
- - The implicit Initialization Vector (IV) is replaced with an
- explicit
- IV to protect against CBC attacks [CBCATT].
-
- - Handling of padding errors is changed to use the bad_record_mac
- alert rather than the decryption_failed alert to protect against
- CBC attacks.
-
- - IANA registries are defined for protocol parameters.
-
- - Premature closes no longer cause a session to be nonresumable.
-
-
-
-Dierks & Rescorla Standards Track [Page 6] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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-
- - Additional informational notes were added for various new attacks
- on TLS.
-
- In addition, a number of minor clarifications and editorial
- improvements were made.
-
-
-
-1.1 Requirements Terminology
-
- Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
- "MAY" that appear in this document are to be interpreted as described
- in RFC 2119 [REQ].
-
-2. Goals
-
- The goals of TLS Protocol, in order of their priority, are:
-
- 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 will then be able to
- 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: to prevent
- the need to create a new protocol (and risking the introduction
- of possible new weaknesses) and to avoid 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 TLS 1.1, TLS 1.0, and SSL 3.0 do not
- interoperate (although each protocol incorporates a mechanism by
- which an implementation can back down prior versions. This document
-
-
-
-Dierks & Rescorla Standards Track [Page 7] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- is intended primarily for readers who will be implementing the
- protocol and 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 nor 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, not to
- have general application beyond that particular goal.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-Dierks & Rescorla Standards Track [Page 8] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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-
-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
- 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 */
-
-
-
-
-
-
-Dierks & Rescorla Standards Track [Page 9] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- Variable length vectors are defined by specifying a subrange of legal
- lengths, inclusively, using the notation <floor..ceiling>. When
- 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.
-
- 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.
-
-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
-
-
-
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-
- 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.
-
- 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]];
-
-
-
-
-
-
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-
- The fields within a structure may be qualified using the type's name
- using 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
-
- 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
-
-
-
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-
- orange VariantRecord
-
- is a narrowed type of a VariantRecord containing a variant_body of
- type V2.
-
-4.7. Cryptographic attributes
-
- The four cryptographic operations digital signing, stream cipher
- encryption, block cipher encryption, and public key encryption are
- designated digitally-signed, stream-ciphered, block-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, a 36-byte structure of two hashes (one SHA and one
- MD5) is signed (encrypted with the private key). It is encoded with
- PKCS #1 block type 0 or type 1 as described in [PKCS1A].
-
- Note: the standard reference for PKCS#1 is now RFC 3447 [PKCS1B].
- However, to minimize differences with TLS 1.0 text, we are using the
- terminology of RFC 2313 [PKCS1A].
-
- In DSS, the 20 bytes of the SHA 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 which are block-ciphered
- will be an exact multiple of the cipher block length.
-
- In public key encryption, a public key algorithm is used to encrypt
-
-
-
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-
- 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.
-
- An RSA encrypted value is encoded with PKCS #1 block type 2 as
- described in [PKCS1A].
-
- 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,
- then the entire structure is encrypted with a stream cipher. The
- length of this structure, in bytes would be equal to 2 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
- due to the fact that 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 function
-
- A number of operations in the TLS record and handshake layer required
- 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 we use for this operation is known as HMAC,
- described in [HMAC].
-
-
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-
- HMAC can be used with a variety of different hash algorithms. TLS
- uses it in the handshake with two different algorithms: MD5 and
- SHA-1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret,
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
- data). Additional hash algorithms can be defined by cipher suites and
- used to protect record data, but MD5 and SHA-1 are hard coded into
- the description of the handshaking for this version of the protocol.
-
- 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.
-
- In order to make the PRF as secure as possible, it uses two hash
- algorithms in a way which should guarantee its security if either
- algorithm remains secure.
-
- First, we define a data expansion function, P_hash(secret, data)
- which 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 was being used to
- create 64 bytes of data, it would have to be iterated 4 times
- (through A(4)), creating 80 bytes of output data; the last 16 bytes
- of the final iteration would then be discarded, leaving 64 bytes of
- output data.
-
- TLS's PRF is created by splitting the secret into two halves and
- using one half to generate data with P_MD5 and the other half to
- generate data with P_SHA-1, then exclusive-or'ing the outputs of
- these two expansion functions together.
-
- S1 and S2 are the two halves of the secret and each is the same
- length. S1 is taken from the first half of the secret, S2 from the
- second half. Their length is created by rounding up the length of the
- overall secret divided by two; thus, if the original secret is an odd
- number of bytes long, the last byte of S1 will be the same as the
- first byte of S2.
-
- L_S = length in bytes of secret;
- L_S1 = L_S2 = ceil(L_S / 2);
-
-
-
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-
-
- The secret is partitioned into two halves (with the possibility of
- one shared byte) as described above, S1 taking the first L_S1 bytes
- and S2 the last L_S2 bytes.
-
- The PRF is then defined as the result of mixing the two pseudorandom
- streams by exclusive-or'ing them together.
-
- PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR
- P_SHA-1(S2, label + seed);
-
- 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
-
- Note that because MD5 produces 16 byte outputs and SHA-1 produces 20
- byte outputs, the boundaries of their internal iterations will not be
- aligned; to generate a 80 byte output will involve P_MD5 being
- iterated through A(5), while P_SHA-1 will only iterate through A(4).
-
-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, 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. Any new record types SHOULD
- allocate type values immediately beyond the ContentType values for
- the four record types described here (see Appendix A.1). All such
- values must be defined by RFC 2434 Standards Action. See section 11
- for IANA Considerations for ContentType values.
-
- 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.
-
-
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-
-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 which 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:
-
- 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 or stream cipher, 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 which 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.
-
-
-
-
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-
- 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 } CipherType;
-
- enum { null, md5, sha } MACAlgorithm;
-
- enum { null(0), (255) } CompressionMethod;
-
- /* The algorithms specified in CompressionMethod,
- BulkCipherAlgorithm, and MACAlgorithm may be added to. */
-
- struct {
- ConnectionEnd entity;
- BulkCipherAlgorithm bulk_cipher_algorithm;
- CipherType cipher_type;
- uint8 key_size;
- uint8 key_material_length;
- MACAlgorithm mac_algorithm;
- uint8 hash_size;
- 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
-
-
-
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-
- 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 the necessary state information
- is 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
- 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 which is 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;
-
-
-
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-
-
- 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 1.1, which uses the version { 3, 2 }. The
- version value 3.2 is historical: TLS version 1.1 is a minor
- modification to the TLS 1.0 protocol, which was itself a minor
- modification to the SSL 3.0 protocol, which bears the version
- value 3.0. (See Appendix A.1).
-
- length
- The length (in bytes) of the following TLSPlaintext.fragment.
- The length should 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.
-
- Note: Data of different TLS Record layer content types MAY be
- interleaved. Application data is generally of higher precedence
- for transmission than other content types and therefore handshake
- records may be held if application data is pending. 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.
-
-
-
-
-
-
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-
- 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 should 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;
-
- 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 (CipherSpec.cipher_type) {
- case stream: GenericStreamCipher;
- case block: GenericBlockCipher;
- } fragment;
- } TLSCiphertext;
-
- type
- The type field is identical to TLSCompressed.type.
-
- version
- The version field is identical to TLSCompressed.version.
-
-
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-
- 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) convert TLSCompressed.fragment structures to and from stream
- TLSCiphertext.fragment structures.
-
- stream-ciphered struct {
- opaque content[TLSCompressed.length];
- opaque MAC[CipherSpec.hash_size];
- } 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
- CipherSpec.hash_size.
-
-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.
-
-
-
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-
-
- block-ciphered struct {
- opaque IV[CipherSpec.block_length];
- opaque content[TLSCompressed.length];
- opaque MAC[CipherSpec.hash_size];
- uint8 padding[GenericBlockCipher.padding_length];
- uint8 padding_length;
- } GenericBlockCipher;
-
- The MAC is generated as described in Section 6.2.3.1.
-
- IV
- Unlike previous versions of SSL and TLS, TLS 1.1 uses an explicit
- IV in order to prevent the attacks described by [CBCATT].
- We recommend the following equivalently strong procedures.
- For clarity we use the following notation.
-
- IV -- the transmitted value of the IV field in the
- GenericBlockCipher structure.
- CBC residue -- the last ciphertext block of the previous record
- mask -- the actual value which the cipher XORs with the
- plaintext prior to encryption of the first cipher block
- of the record.
-
- In prior versions of TLS, there was no IV field and the CBC residue
- and mask were one and the same. See Sections 6.1, 6.2.3.2 and 6.3,
- of [TLS1.0] for details of TLS 1.0 IV handling.
-
- One of the following two algorithms SHOULD be used to generate the
- per-record IV:
-
- (1) Generate a cryptographically strong random string R of
- length CipherSpec.block_length. Place R
- in the IV field. Set the mask to R. Thus, the first
- cipher block will be encrypted as E(R XOR Data).
-
- (2) Generate a cryptographically strong random number R of
- length CipherSpec.block_length and prepend it to the plaintext
- prior to encryption. In
- this case either:
-
- (a) The cipher may use a fixed mask such as zero.
- (b) The CBC residue from the previous record may be used
- as the mask. This preserves maximum code compatibility
- with TLS 1.0 and SSL 3. It also has the advantage that
- it does not require the ability to quickly reset the IV,
- which is known to be a problem on some systems.
-
- In either 2(a) or 2(b) the data (R || data) is fed into the
-
-
-
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-
-
- encryption process. The first cipher block (containing
- E(mask XOR R) is placed in the IV field. The first
- block of content contains E(IV XOR data)
-
- The following alternative procedure MAY be used: However, it has
- not been demonstrated to be equivalently cryptographically strong
- to the above procedures. The sender prepends a fixed block F to
- the plaintext (or alternatively a block generated with a weak
- PRNG). He then encrypts as in (2) above, using the CBC residue
- from the previous block as the mask for the prepended block. Note
- that in this case the mask for the first record transmitted by
- the application (the Finished) MUST be generated using a
- cryptographically strong PRNG.
-
- The decryption operation for all three alternatives is the same.
- The receiver 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 long, 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, CipherSpec.hash_size, 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, 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
-
-
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-
- 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].
-
- 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 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.
-
-6.3. 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, which are generated from the master secret in
- that order. Unused values are empty.
-
- When generating keys and MAC secrets, the master secret is used as an
- entropy source.
-
- To generate the key material, compute
-
- key_block = PRF(SecurityParameters.master_secret,
- "key expansion",
- SecurityParameters.server_random +
-
-
-
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-
-
- SecurityParameters.client_random);
-
- until enough output has been generated. Then the key_block is
- partitioned as follows:
-
- client_write_MAC_secret[SecurityParameters.hash_size]
- server_write_MAC_secret[SecurityParameters.hash_size]
- client_write_key[SecurityParameters.key_material_length]
- server_write_key[SecurityParameters.key_material_length]
-
-
- Implementation note:
- The currently defined 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 which are used to allow peers to agree
- upon security parameters for the record layer, authenticate
- themselves, instantiate negotiated security parameters, and
- 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.
-
-
-
-
-
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-
- 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 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 7.4.9).
-
- 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
-
-
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-
-
- 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(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),
- (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
- This message notifies the recipient that the sender will not send
-
-
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-
-
- 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 an 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
- This alert is returned if a record is received with an incorrect
-
-
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-
-
- 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
- This alert MAY be returned if 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.
-
- Note: Differentiating between bad_record_mac and
- decryption_failed alerts may permit certain attacks against CBC
- mode as used in TLS [CBCATT]. It is preferable to uniformly use
- the bad_record_mac alert to hide the specific type of the error.
-
-
- record_overflow
- A TLSCiphertext record was received which 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 in TLS. It should 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.
-
-
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-
- certificate_unknown
- Some other (unspecified) issue arose in processing the
- certificate, rendering it unacceptable.
-
- illegal_parameter
- 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 TLS 1.0 but not TLS 1.1.
-
- 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 makes it impossible to continue (such as a memory
- allocation failure). This message is always fatal.
-
-
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-
-
- user_canceled
- This handshake is being canceled for some reason unrelated to a
- protocol failure. If the user cancels an operation after the
- 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 would be 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.
-
- 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 alerts values MUST be defined by RFC 2434 Standards Action. See
- Section 11 for IANA Considerations for alert values.
-
-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.
-
- - Exchange certificates and cryptographic information to allow the
-
-
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-
-
- 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 TLS always
- negotiating the strongest possible connection between two peers:
- there are a number of ways 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.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
- However, you SHOULD never send data over a link encrypted with 40 bit
- security unless you feel that data is worth no more than the effort
- required to break that encryption.
-
- 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 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 which range from 48 to 128 bytes in
- length.
-
- 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. Now 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 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
-
-
-
-
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-
-
- 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*
- ServerKeyExchange*
- CertificateRequest*
- <-------- ServerHelloDone
- Certificate*
- 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
- perform a full handshake.
-
-
-
-
-
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-
-
- 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;
- case finished: Finished;
- } body;
- } Handshake;
-
-
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-
-
- 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 which 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 type values MUST be defined via RFC 2434
- Standards Action. See Section 11 for IANA Considerations for these
- values.
-
-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 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 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;
-
-
-
-
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-
-
- Note: This message MUST NOT be included in the message hashes which 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 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, while the third option 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 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.
-
-
-
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-
-
- 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) and a MAC algorithm. 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>;
- } ClientHello;
-
- 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 3.2 (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 the
-
-
-
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-
-
- 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.
-
- 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.
-
- Forward compatibility note:
- In the interests of forward compatibility, it is permitted for a
- client hello message to include extra data after the compression
- methods. This data MUST be included in the handshake hashes, but
- must otherwise be ignored. This is the only handshake message for
- which this is legal; for all other messages, the amount of data
- in the message MUST match the description of the message
- precisely.
-
-Note: For the intended use of trailing data in the ClientHello, see RFC
- 3546 [TLSEXT].
-
-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;
-
-
-
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-
-
- CompressionMethod compression_method;
- } 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).
-
- 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.
-
- 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.
-
-7.4.2. Server certificate
-
- When this message will be sent:
- The server MUST send a certificate whenever the agreed-upon key
- exchange method is not an anonymous one. 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
-
-
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-
-
- certificate. It MUST contain a key which 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.
-
- 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 which 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, 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 which 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 which specifies the
- root certificate authority may optionally be omitted from the
- chain, under the assumption that the remote end must already
-
-
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-
-
- 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
- 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: either an RSA public
- key to encrypt the premaster secret with, or a Diffie-Hellman
- public key with which the client can complete a key exchange
- (with the result being the premaster secret.)
-
- As additional CipherSuites are defined for TLS which 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.
-
-
-
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-
-
- Structure of this message:
- enum { rsa, diffie_hellman } KeyExchangeAlgorithm;
-
- struct {
- opaque rsa_modulus<1..2^16-1>;
- opaque rsa_exponent<1..2^16-1>;
- } ServerRSAParams;
-
- rsa_modulus
- The modulus of the server's temporary RSA key.
-
- rsa_exponent
- The public exponent of the server's temporary RSA key.
-
- 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;
- case rsa:
- ServerRSAParams params;
- Signature signed_params;
- };
- } ServerKeyExchange;
-
- struct {
- select (KeyExchangeAlgorithm) {
- case diffie_hellman:
- ServerDHParams params;
- case rsa:
- ServerRSAParams params;
- };
- } ServerParams;
-
-
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-
- 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.
-
- md5_hash
- MD5(ClientHello.random + ServerHello.random + ServerParams);
-
- sha_hash
- SHA(ClientHello.random + ServerHello.random + ServerParams);
-
- enum { anonymous, rsa, dsa } SignatureAlgorithm;
-
-
- struct {
- select (SignatureAlgorithm) {
- case anonymous: struct { };
- case rsa:
- digitally-signed struct {
- opaque md5_hash[16];
- opaque sha_hash[20];
- };
- 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)
-
-
-
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-
-
- } ClientCertificateType;
-
- opaque DistinguishedName<1..2^16-1>;
-
- struct {
- ClientCertificateType certificate_types<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.
-
- 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.
-
-
- ClientCertificateType values are divided into three groups:
-
- 1. Values from 0 (zero) through 63 decimal (0x3F) inclusive are
- reserved for IETF Standards Track protocols.
-
- 2. Values from 64 decimal (0x40) through 223 decimal (0xDF) inclusive
- are reserved for assignment for non-Standards Track methods.
-
- 3. Values from 224 decimal (0xE0) through 255 decimal (0xFF)
- inclusive are reserved for private use.
-
- Additional information describing the role of IANA in the
- allocation of ClientCertificateType code points is 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.
-
-
-
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-
-
-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
- 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.
-
-
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-
-
- 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 which will allow each
- 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 which 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 or the temporary RSA
- key provided in a server key exchange message, and sends the
- result in an encrypted premaster secret message. This structure
- is a variant of the client key exchange message, 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.
-
-
-
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-
-
- random
- 46 securely-generated random bytes.
-
- struct {
- public-key-encrypted PreMasterSecret pre_master_secret;
- } 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.
-
- Note: 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.
-
- The best way to avoid vulnerability to this attack is to 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.
-
-
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-
-
- 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 which use static RSA
- keys SHOULD 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, 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 should randomize the PreMasterSecret in case
- of error, rather than generate an alert, in order to avoid
- variants on the Bleichenbacher attack. [KPR03]
-
-7.4.7.2. 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, 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 MUST be empty.
-
- explicit
- Yc needs to be sent.
-
- struct {
- select (PublicValueEncoding) {
-
-
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-
-
- 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).
-
-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.
-
- CertificateVerify.signature.md5_hash
- MD5(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
-
-
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-
-
- 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.
-
- struct {
- opaque verify_data[12];
- } Finished;
-
- verify_data
- PRF(master_secret, finished_label, MD5(handshake_messages) +
- SHA-1(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".
-
- 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 7.4.8 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 which 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
-
-
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-
- 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
- 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.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
-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.
-
- RSA digital signatures are performed using PKCS #1 [PKCS1] block type
- 1. RSA public key encryption is performed using PKCS #1 block type 2.
-
-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.
-
-11. IANA Considerations
-
- This document describes a number of new registries to be created by
- IANA. We recommend that they be placed as individual registries items
- under a common TLS category.
-
- Section 7.4.3 describes a TLS ClientCertificateType Registry to be
- maintained by the IANA, as defining a number of such code point
- identifiers. ClientCertificateType identifiers with values in the
- range 0-63 (decimal) inclusive are assigned via RFC 2434 Standards
- Action. Values from the range 64-223 (decimal) inclusive are assigned
- via [RFC 2434] Specification Required. Identifier values from
-
-
-
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-
-
- 224-255 (decimal) inclusive are reserved for RFC 2434 Private Use.
- The registry will be initially populated with the values in this
- document, Section 7.4.4.
-
- Section A.5 describes a TLS Cipher Suite Registry to be maintained by
- the IANA, as well as defining a number of such cipher suite
- identifiers. Cipher suite values with the first byte in the range
- 0-191 (decimal) inclusive are assigned via RFC 2434 Standards Action.
- Values with the first byte in the range 192-254 (decimal) are
- assigned via RFC 2434 Specification Required. Values with the first
- byte 255 (decimal) are reserved for RFC 2434 Private Use. The
- registry will be initially populated with the values from Section A.5
- of this document, [TLSAES], and Section 3 of [TLSKRB].
-
- Section 6 requires that all ContentType values be defined by RFC 2434
- Standards Action. IANA SHOULD create a TLS ContentType registry,
- initially populated with values from Section 6.2.1 of this document.
- Future values MUST be allocated via Standards Action as described in
- [RFC 2434].
-
- Section 7.2.2 requires that all Alert values be defined by RFC 2434
- Standards Action. IANA SHOULD create a TLS Alert registry, initially
- populated with values from Section 7.2 of this document and Section 4
- of [TLSEXT]. Future values MUST be allocated via Standards Action as
- described in [RFC 2434].
-
- Section 7.4 requires that all HandshakeType values be defined by RFC
- 2434 Standards Action. IANA SHOULD create a TLS HandshakeType
- registry, initially populated with values from Section 7.4 of this
- document and Section 2.4 of [TLSEXT]. Future values MUST be
- allocated via Standards Action as described in [RFC2434].
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
-A. Protocol constant values
-
- This section describes protocol types and constants.
-
-A.1. Record layer
-
- struct {
- uint8 major, minor;
- } ProtocolVersion;
-
- ProtocolVersion version = { 3, 2 }; /* TLS v1.1 */
-
- 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 (CipherSpec.cipher_type) {
- case stream: GenericStreamCipher;
- case block: GenericBlockCipher;
- } fragment;
- } TLSCiphertext;
-
- stream-ciphered struct {
- opaque content[TLSCompressed.length];
- opaque MAC[CipherSpec.hash_size];
- } GenericStreamCipher;
-
- block-ciphered struct {
- opaque IV[CipherSpec.block_length];
-
-
-
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-
-
- opaque content[TLSCompressed.length];
- opaque MAC[CipherSpec.hash_size];
- uint8 padding[GenericBlockCipher.padding_length];
- uint8 padding_length;
- } GenericBlockCipher;
-
-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),
- (255)
- } AlertDescription;
-
- struct {
- AlertLevel level;
- AlertDescription description;
- } Alert;
-
-
-
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-
-
-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>;
- CompressionMethod compression_methods<1..2^8-1>;
-
-
-
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-
-
- } ClientHello;
-
- struct {
- ProtocolVersion server_version;
- Random random;
- SessionID session_id;
- CipherSuite cipher_suite;
- CompressionMethod compression_method;
- } ServerHello;
-
-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;
-
- enum { rsa, diffie_hellman } KeyExchangeAlgorithm;
-
- struct {
- opaque rsa_modulus<1..2^16-1>;
- opaque rsa_exponent<1..2^16-1>;
- } ServerRSAParams;
-
- 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) {
- case diffie_hellman:
- ServerDHParams params;
- Signature signed_params;
- case rsa:
- ServerRSAParams params;
- Signature signed_params;
- };
- } ServerKeyExchange;
-
- enum { anonymous, rsa, dsa } SignatureAlgorithm;
-
- struct {
- select (KeyExchangeAlgorithm) {
- case diffie_hellman:
- ServerDHParams params;
-
-
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-
-
- case rsa:
- ServerRSAParams params;
- };
- } ServerParams;
-
- struct {
- select (SignatureAlgorithm) {
- case anonymous: struct { };
- case rsa:
- digitally-signed struct {
- opaque md5_hash[16];
- opaque sha_hash[20];
- };
- 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 {
- select (KeyExchangeAlgorithm) {
- case rsa: EncryptedPreMasterSecret;
- case diffie_hellman: ClientDiffieHellmanPublic;
- } exchange_keys;
- } ClientKeyExchange;
-
- struct {
- ProtocolVersion client_version;
-
-
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-
-
- 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 };
-
- 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 };
-
-
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-
-
- 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 };
-
- 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 };
-
- 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 and is
- therefore deprecated.
-
- 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 };
-
- 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 1.1 implementations MUST NOT negotiate these
- cipher suites in TLS 1.1 mode. However, for backward compatibility
- they may be offered in the ClientHello for use with TLS 1.0 or SSLv3
- only servers. TLS 1.1 clients MUST check that the server did not
- choose one of these cipher suites during the handshake. These
-
-
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-
-
- 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:
-
- 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 1.1 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
- };
-
- The following cipher suites were defined in [TLSAES] and are included
- here for completeness. See [TLSAES] for details:
-
- CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F };
- CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x30 };
- CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x31 };
-
-
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-
-
- 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_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x34 };
-
- CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x35 };
- 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 };
- CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00, 0x3A };
-
- The cipher suite space is divided into three regions:
-
- 1. Cipher suite values with first byte 0x00 (zero)
- through decimal 191 (0xBF) inclusive are reserved for the IETF
- Standards Track protocols.
-
- 2. Cipher suite values with first byte decimal 192 (0xC0)
- through decimal 254 (0xFE) inclusive are reserved
- for assignment for non-Standards Track methods.
-
- 3. Cipher suite values with first byte 0xFF are
- reserved for private use.
- Additional information describing the role of IANA in the allocation
- of cipher suite code points is 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;
-
- enum { null, md5, sha } MACAlgorithm;
-
- /* The algorithms specified in CompressionMethod,
-
-
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-
-
- BulkCipherAlgorithm, and MACAlgorithm may be added to. */
-
- struct {
- ConnectionEnd entity;
- BulkCipherAlgorithm bulk_cipher_algorithm;
- CipherType cipher_type;
- uint8 key_size;
- uint8 key_material_length;
- MACAlgorithm mac_algorithm;
- uint8 hash_size;
- CompressionMethod compression_algorithm;
- opaque master_secret[48];
- opaque client_random[32];
- opaque server_random[32];
- } SecurityParameters;
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
-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.
-
- 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
- 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
-
-
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-
-
- 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
- vector is exclusive-ORed with the first plaintext block prior to
- encryption.
-
-
-
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-Dierks & Rescorla Standards Track [Page 68] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
-
-
- 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.
-
-
-
-
-
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-
-
- 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, which 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.
-
-
-
-
-
-
-
-
-
-
-
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-
-
-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_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
-
- 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
- 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
-
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- 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
- How much data needs 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
-
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-
-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. To seed 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
- which provide no or minimal security. A proper implementation will
- probably not support many cipher suites. For example, 40-bit
- encryption is easily broken, so implementations requiring strong
- security should not allow 40-bit keys. Similarly, 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.
-
-
-
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-E. Backward Compatibility With SSL
-
- For historical reasons and in order to avoid a profligate consumption
- of reserved port numbers, application protocols which are secured by
- TLS 1.1, TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share the same
- connection port: for example, the https protocol (HTTP secured by SSL
- or TLS) uses port 443 regardless of which security protocol it is
- using. Thus, some mechanism must be determined to distinguish and
- negotiate among the various protocols.
-
- TLS versions 1.1, 1.0, and SSL 3.0 are very similar; thus, supporting
- both is easy. TLS clients who wish to negotiate with such older
- servers SHOULD send client hello messages using the SSL 3.0 record
- format and client hello structure, sending {3, 2} for the version
- field to note that they support TLS 1.1. If the server supports only
- TLS 1.0 or SSL 3.0, it will respond with a downrev 3.0 server hello;
- if it supports TLS 1.1 it will respond with a TLS 1.1 server hello.
- The negotiation then proceeds as appropriate for the negotiated
- protocol.
-
- Similarly, a TLS 1.1 server which wishes to interoperate with TLS
- 1.0 or SSL 3.0 clients SHOULD accept SSL 3.0 client hello messages
- and respond with a SSL 3.0 server hello if an SSL 3.0 client hello
- with a version field of {3, 0} is received, denoting that this client
- does not support TLS. Similarly, if a SSL 3.0 or TLS 1.0 hello with a
- version field of {3, 1} is received, the server SHOULD respond with a
- TLS 1.0 hello with a version field of {3, 1}.
-
- 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.
-
- TLS 1.1 clients that support SSL Version 2.0 servers MUST send SSL
- Version 2.0 client hello messages [SSL2]. TLS servers SHOULD accept
- either client hello format if they wish to support SSL 2.0 clients on
- the same connection port. The only deviations from the Version 2.0
- specification are the ability to specify a version with a value of
- three and the support for more ciphering types in the CipherSpec.
-
- Warning: The ability to send Version 2.0 client hello messages will be
- phased out with all due haste. Implementors SHOULD make every
- effort to move forward as quickly as possible. Version 3.0
- provides better mechanisms for moving to newer versions.
-
- The following cipher specifications are carryovers from SSL Version
- 2.0. These are assumed to use RSA for key exchange and
- authentication.
-
-
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- V2CipherSpec TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 };
- V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 };
- V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 };
- V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5
- = { 0x04,0x00,0x80 };
- V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 };
- V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 };
- V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };
-
- Cipher specifications native to TLS can be included in Version 2.0
- client hello messages using the syntax below. Any V2CipherSpec
- element with its first byte equal to zero will be ignored by Version
- 2.0 servers. Clients sending any of the above V2CipherSpecs SHOULD
- also include the TLS equivalent (see Appendix A.5):
-
- V2CipherSpec (see TLS name) = { 0x00, CipherSuite };
-
- Note: TLS 1.1 clients may generate the SSLv2 EXPORT cipher suites in
- handshakes for backward compatibility but MUST NOT negotiate them in
- TLS 1.1 mode.
-
-E.1. Version 2 client hello
-
- The Version 2.0 client hello message is presented below using this
- document's presentation model. The true definition is still assumed
- to be the SSL Version 2.0 specification. Note that this message MUST
- be sent directly on the wire, not wrapped as an SSLv3 record
-
- uint8 V2CipherSpec[3];
-
- 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
- This field is the length of the following data in bytes. The high
- bit MUST be 1 and is not part of the length.
-
- msg_type
- This field, in conjunction with the version field, identifies a
-
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- version 2 client hello message. The value SHOULD be one (1).
-
- version
- The highest version of the protocol supported by the client
- (equals ProtocolVersion.version, see Appendix A.1).
-
- 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.
-
- challenge_length
- The length in bytes of the client's challenge to the server to
- authenticate itself. 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. There MUST be at least one CipherSpec acceptable to the
- server.
-
- session_id
- This field MUST be empty.
-
- challenge
- The client challenge to the server for the server to identify
- itself is a (nearly) arbitrary length random. The TLS server will
- right justify the challenge data to become the ClientHello.random
- data (padded with leading zeroes, if necessary), as specified in
- this protocol specification. If the length of the challenge is
- greater than 32 bytes, only the last 32 bytes are used. It is
- legitimate (but not necessary) for a V3 server to reject a V2
- ClientHello that has fewer than 16 bytes of challenge data.
-
- 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
-
-
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- 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.
-
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-
-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 7.4.8, 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
-
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- from the server key exchange message. The result is sent in a client
- 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 may be either contained in the server's certificate or may
- be a temporary RSA key sent in a server key exchange message. When
- temporary RSA keys are used, they are signed by the server's RSA
- certificate. The signature includes the current ClientHello.random,
- so old signatures and temporary keys cannot be replayed. Servers may
- use a single temporary RSA key for multiple negotiation sessions.
-
- Note: The temporary RSA key option is useful if servers need large
- certificates but must comply with government-imposed size limits
- on keys used for key exchange.
-
- Note that if ephemeral RSA is not used, 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
-
-
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- the certificate verify message (see Section 7.4.8). 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
- can use the server key exchange message to send a set of temporary
- Diffie-Hellman parameters signed with a DSS or RSA certificate.
- 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 so 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
-
-
-
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-
- 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. Parties
- concerned about attacks of this scale should not be using 40-bit
- encryption keys anyway. Altering the padding of the least-significant
- 8 bytes of the PKCS padding does 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
-
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- 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. MD5 and SHA
-
- TLS uses hash functions very conservatively. Where possible, both MD5
- and SHA are used in tandem to ensure that non-catastrophic flaws in
- one algorithm will not break the overall protocol.
-
-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.
-
-
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-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
- 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].
-
-
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-
-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, terminating connections, or
- forge partial TLS records, causing the connection to stall.
- These 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, 40-bit
- bulk encryption 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.
-
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-Dierks & Rescorla Standards Track [Page 84] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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-
-Security Considerations
-
- Security issues are discussed throughout this memo, especially in
- Appendices D, E, and F.
-
-Normative References
- [AES] National Institute of Standards and Technology,
- "Specification for the Advanced Encryption Standard (AES)"
- FIPS 197. November 26, 2001.
-
- [3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To DES,"
- IEEE Spectrum, v. 16, n. 7, July 1979, pp40-41.
-
- [DES] ANSI X3.106, "American National Standard for Information
- Systems-Data Link Encryption," American National Standards
- Institute, 1983.
-
- [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.
-
- [IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH
- Series in Information Processing, v. 1, Konstanz: Hartung-
- Gorre Verlag, 1992.
-
- [MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,
- April 1992.
-
- [PKCS1A] B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1:
- RSA Cryptography Specifications Version 1.5", RFC 2313,
- March 1998.
-
- [PKCS1B] J. Jonsson, B. Kaliski, "Public-Key Cryptography Standards
- (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC
- 3447, February 2003.
-
- [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, January 1998.
-
- [SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms,
-
-
-
-Dierks & Rescorla Standards Track [Page 85] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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-
- 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] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
- Considerations Section in RFCs", RFC 3434, 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.
- [TLSKRB] A. Medvinsky, M. Hur, "Addition of Kerberos Cipher Suites to
- Transport Layer Security (TLS)", RFC 2712, October 1999.
-
-
-Informative References
-
- [AH] Kent, S., and Atkinson, R., "IP Authentication Header", RFC
- 2402, November 1998.
-
- [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.
-
- [ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication
- for Protecting Communications (Or: How Secure is SSL?)",
- Crypto 2001.
-
- [ESP] Kent, S., and Atkinson, R., "IP Encapsulating Security
- Payload (ESP)", RFC 2406, November 1998.
-
- [KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based
-
-
-
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-
- 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] D. Eastlake 3rd, S. Crocker, J. Schiller. "Randomness
- Recommendations for Security", RFC 1750, December 1994.
-
- [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] R. Zuccherato, "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 Allen, C., "The TLS Protocol, Version 1.0",
- RFC 2246, January 1999.
-
- [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] R. Srinivansan, Sun Microsystems, "XDR: External Data
- Representation Standard", RFC 1832, August 1995.
-
-
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-
-Credits
-
- Working Group Chairs
- Win Treese
- EMail: treese@acm.org
-
- Eric Rescorla
- EMail: ekr@rtfm.com
-
-
- Editors
-
- Tim Dierks Eric Rescorla
- Independent RTFM, Inc.
-
- EMail: tim@dierks.org EMail: ekr@rtfm.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
-
- Ran Canetti
- IBM
- canetti@watson.ibm.com
-
- Taher Elgamal
- taher@securify.com
- Securify
-
- Anil Gangolli
- anil@busybuddha.org
-
- Kipp Hickman
-
- Phil Karlton (co-author of SSLv3)
-
- Paul Kocher (co-author of SSLv3)
- Cryptography Research
- paul@cryptography.com
-
-
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-Dierks & Rescorla Standards Track [Page 88] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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- Hugo Krawczyk
- Technion Israel Institute of Technology
- hugo@ee.technion.ac.il
-
- Robert Relyea
- Netscape Communications
- relyea@netscape.com
-
- Jim Roskind
- Netscape Communications
- jar@netscape.com
-
- Michael Sabin
-
- Dan Simon
- Microsoft, Inc.
- dansimon@microsoft.com
-
- Tom Weinstein
-
-Comments
-
- The discussion list for the IETF TLS working group is located at the
- e-mail address <ietf-tls@lists.consensus.com>. Information on the
- group and information on how to subscribe to the list is at
- <http://lists.consensus.com/>.
-
- Archives of the list can be found at:
- <http://www.imc.org/ietf-tls/mail-archive/>
-
-
-
-
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-Dierks & Rescorla Standards Track [Page 89] draft-ietf-tls-rfc2246-bis-13.txt TLS June 2005
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-Full Copyright Statement
-
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- Intellectual Property Rights or other rights that might be claimed to
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