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+Network Working Group                                          D. Taylor
+Request for Comments: 5054                                   Independent
+Category: Informational                                            T. Wu
+                                                                   Cisco
+                                                    N. Mavrogiannopoulos
+                                                               T. Perrin
+                                                             Independent
+                                                           November 2007
+
+
+ Using the Secure Remote Password (SRP) Protocol for TLS Authentication
+
+Status of This Memo
+
+   This memo provides information for the Internet community.  It does
+   not specify an Internet standard of any kind.  Distribution of this
+   memo is unlimited.
+
+Abstract
+
+   This memo presents a technique for using the Secure Remote Password
+   protocol as an authentication method for the Transport Layer Security
+   protocol.
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+Taylor, et al.               Informational                      [Page 1]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+Table of Contents
+
+   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
+   2.  SRP Authentication in TLS  . . . . . . . . . . . . . . . . . .  3
+     2.1.  Notation and Terminology . . . . . . . . . . . . . . . . .  3
+     2.2.  Handshake Protocol Overview  . . . . . . . . . . . . . . .  4
+     2.3.  Text Preparation . . . . . . . . . . . . . . . . . . . . .  5
+     2.4.  SRP Verifier Creation  . . . . . . . . . . . . . . . . . .  5
+     2.5.  Changes to the Handshake Message Contents  . . . . . . . .  5
+       2.5.1.  Client Hello . . . . . . . . . . . . . . . . . . . . .  6
+       2.5.2.  Server Certificate . . . . . . . . . . . . . . . . . .  7
+       2.5.3.  Server Key Exchange  . . . . . . . . . . . . . . . . .  7
+       2.5.4.  Client Key Exchange  . . . . . . . . . . . . . . . . .  8
+     2.6.  Calculating the Premaster Secret . . . . . . . . . . . . .  8
+     2.7.  Ciphersuite Definitions  . . . . . . . . . . . . . . . . .  9
+     2.8.  New Message Structures . . . . . . . . . . . . . . . . . .  9
+       2.8.1.  Client Hello . . . . . . . . . . . . . . . . . . . . . 10
+       2.8.2.  Server Key Exchange  . . . . . . . . . . . . . . . . . 10
+       2.8.3.  Client Key Exchange  . . . . . . . . . . . . . . . . . 11
+     2.9.  Error Alerts . . . . . . . . . . . . . . . . . . . . . . . 11
+   3.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
+     3.1.  General Considerations for Implementors  . . . . . . . . . 12
+     3.2.  Accepting Group Parameters . . . . . . . . . . . . . . . . 12
+     3.3.  Protocol Characteristics . . . . . . . . . . . . . . . . . 12
+     3.4.  Hash Function Considerations . . . . . . . . . . . . . . . 13
+   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
+   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
+     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
+     5.2.  Informative References . . . . . . . . . . . . . . . . . . 15
+   Appendix A.  SRP Group Parameters  . . . . . . . . . . . . . . . . 16
+   Appendix B.  SRP Test Vectors  . . . . . . . . . . . . . . . . . . 21
+   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 22
+
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+Taylor, et al.               Informational                      [Page 2]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+1.  Introduction
+
+   At the time of writing TLS [TLS] uses public key certificates, pre-
+   shared keys, or Kerberos for authentication.
+
+   These authentication methods do not seem well suited to certain
+   applications now being adapted to use TLS ([IMAP], for example).
+   Given that many protocols are designed to use the user name and
+   password method of authentication, being able to safely use user
+   names and passwords provides an easier route to additional security.
+
+   SRP ([SRP], [SRP-6]) is an authentication method that allows the use
+   of user names and passwords over unencrypted channels without
+   revealing the password to an eavesdropper.  SRP also supplies a
+   shared secret at the end of the authentication sequence that can be
+   used to generate encryption keys.
+
+   This document describes the use of the SRP authentication method for
+   TLS.
+
+   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+   document are to be interpreted as described in RFC 2119 [REQ].
+
+2.  SRP Authentication in TLS
+
+2.1.  Notation and Terminology
+
+   The version of SRP used here is sometimes referred to as "SRP-6"
+   [SRP-6].  This version is a slight improvement over "SRP-3", which
+   was described in [SRP] and [SRP-RFC].  For convenience, this document
+   and [SRP-RFC] include the details necessary to implement SRP-6;
+   [SRP-6] is cited for informative purposes only.
+
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+Taylor, et al.               Informational                      [Page 3]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   This document uses the variable names defined in [SRP-6]:
+
+      N, g: group parameters (prime and generator)
+
+      s: salt
+
+      B, b: server's public and private values
+
+      A, a: client's public and private values
+
+      I: user name (aka "identity")
+
+      P: password
+
+      v: verifier
+
+      k: SRP-6 multiplier
+
+   The | symbol indicates string concatenation, the ^ operator is the
+   exponentiation operation, and the % operator is the integer remainder
+   operation.
+
+   Conversion between integers and byte-strings assumes the most
+   significant bytes are stored first, as per [TLS] and [SRP-RFC].  In
+   the following text, if a conversion from integer to byte-string is
+   implicit, the most significant byte in the resultant byte-string MUST
+   be non-zero.  If a conversion is explicitly specified with the
+   operator PAD(), the integer will first be implicitly converted, then
+   the resultant byte-string will be left-padded with zeros (if
+   necessary) until its length equals the implicitly-converted length of
+   N.
+
+2.2.  Handshake Protocol Overview
+
+   The advent of [SRP-6] allows the SRP protocol to be implemented using
+   the standard sequence of handshake messages defined in [TLS].
+
+   The parameters to various messages are given in the following
+   diagram.
+
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+Taylor, et al.               Informational                      [Page 4]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   Client                                            Server
+
+   Client Hello (I)        -------->
+                                               Server Hello
+                                               Certificate*
+                                        Server Key Exchange (N, g, s, B)
+                           <--------      Server Hello Done
+   Client Key Exchange (A) -------->
+   [Change cipher spec]
+   Finished                -------->
+                                       [Change cipher spec]
+                           <--------               Finished
+
+   Application Data        <------->       Application Data
+
+   * Indicates an optional message that is not always sent.
+
+                                 Figure 1
+
+2.3.  Text Preparation
+
+   The user name and password strings SHALL be UTF-8 encoded Unicode,
+   prepared using the [SASLPREP] profile of [STRINGPREP].
+
+2.4.  SRP Verifier Creation
+
+   The verifier is calculated as described in Section 3 of [SRP-RFC].
+   We give the algorithm here for convenience.
+
+   The verifier (v) is computed based on the salt (s), user name (I),
+   password (P), and group parameters (N, g).  The computation uses the
+   [SHA1] hash algorithm:
+
+        x = SHA1(s | SHA1(I | ":" | P))
+        v = g^x % N
+
+2.5.  Changes to the Handshake Message Contents
+
+   This section describes the changes to the TLS handshake message
+   contents when SRP is being used for authentication.  The definitions
+   of the new message contents and the on-the-wire changes are given in
+   Section 2.8.
+
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+Taylor, et al.               Informational                      [Page 5]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+2.5.1.  Client Hello
+
+   The user name is appended to the standard client hello message using
+   the extension mechanism defined in [TLSEXT] (see Section 2.8.1).
+   This user name extension is henceforth called the "SRP extension".
+   The following subsections give details of its use.
+
+2.5.1.1.  Session Resumption
+
+   When a client attempts to resume a session that uses SRP
+   authentication, the client MUST include the SRP extension in the
+   client hello message, in case the server cannot or will not allow
+   session resumption, meaning a full handshake is required.
+
+   If the server does agree to resume an existing session, the server
+   MUST ignore the information in the SRP extension of the client hello
+   message, except for its inclusion in the finished message hashes.
+   This is to ensure that attackers cannot replace the authenticated
+   identity without supplying the proper authentication information.
+
+2.5.1.2.  Missing SRP Extension
+
+   The client may offer SRP cipher suites in the hello message but omit
+   the SRP extension.  If the server would like to select an SRP cipher
+   suite in this case, the server SHOULD return a fatal
+   "unknown_psk_identity" alert (see Section 2.9) immediately after
+   processing the client hello message.
+
+   A client receiving this alert MAY choose to reconnect and resend the
+   hello message, this time with the SRP extension.  This allows the
+   client to advertise that it supports SRP, but not have to prompt the
+   user for his user name and password, nor expose the user name in the
+   clear, unless necessary.
+
+2.5.1.3.  Unknown SRP         User Name
+
+   If the server doesn't have a verifier for the user name in the SRP
+   extension, the server MAY abort the handshake with an
+   "unknown_psk_identity" alert (see Section 2.9).  Alternatively, if
+   the server wishes to hide the fact that this user name doesn't have a
+   verifier, the server MAY simulate the protocol as if a verifier
+   existed, but then reject the client's finished message with a
+   "bad_record_mac" alert, as if the password was incorrect.
+
+   To simulate the existence of an entry for each user name, the server
+   must consistently return the same salt (s) and group (N, g) values
+   for the same user name.  For example, the server could store a secret
+   "seed key" and then use HMAC-SHA1(seed_key, "salt" | user_name) to
+
+
+
+Taylor, et al.               Informational                      [Page 6]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   generate the salts [HMAC].  For B, the server can return a random
+   value between 1 and N-1 inclusive.  However, the server should take
+   care to simulate computation delays.  One way to do this is to
+   generate a fake verifier using the "seed key" approach, and then
+   proceed with the protocol as usual.
+
+2.5.2.  Server Certificate
+
+   The server MUST send a certificate if it agrees to an SRP cipher
+   suite that requires the server to provide additional authentication
+   in the form of a digital signature.  See Section 2.7 for details of
+   which cipher suites defined in this document require a server
+   certificate to be sent.
+
+2.5.3.  Server Key Exchange
+
+   The server key exchange message contains the prime (N), the generator
+   (g), and the salt value (s) read from the SRP password file based on
+   the user name (I) received in the client hello extension.
+
+   The server key exchange message also contains the server's public
+   value (B).  The server calculates this value as B = k*v + g^b % N,
+   where b is a random number that SHOULD be at least 256 bits in length
+   and k = SHA1(N | PAD(g)).
+
+   If the server has sent a certificate message, the server key exchange
+   message MUST be signed.
+
+   The group parameters (N, g) sent in this message MUST have N as a
+   safe prime (a prime of the form N=2q+1, where q is also prime).  The
+   integers from 1 to N-1 will form a group under multiplication % N,
+   and g MUST be a generator of this group.  In addition, the group
+   parameters MUST NOT be specially chosen to allow efficient
+   computation of discrete logarithms.
+
+   The SRP group parameters in Appendix A satisfy the above
+   requirements, so the client SHOULD accept any parameters from this
+   appendix that have large enough N values to meet her security
+   requirements.
+
+   The client MAY accept other group parameters from the server, if the
+   client has reason to believe that these parameters satisfy the above
+   requirements, and the parameters have large enough N values.  For
+   example, if the parameters transmitted by the server match parameters
+   on a "known-good" list, the client may choose to accept them.  See
+   Section 3 for additional security considerations relevant to the
+   acceptance of the group parameters.
+
+
+
+
+Taylor, et al.               Informational                      [Page 7]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   Group parameters that are not accepted via one of the above methods
+   MUST be rejected with an "insufficient_security" alert (see
+   Section 2.9).
+
+   The client MUST abort the handshake with an "illegal_parameter" alert
+   if B % N = 0.
+
+2.5.4.  Client Key Exchange
+
+   The client key exchange message carries the client's public value
+   (A).  The client calculates this value as A = g^a % N, where a is a
+   random number that SHOULD be at least 256 bits in length.
+
+   The server MUST abort the handshake with an "illegal_parameter" alert
+   if A % N = 0.
+
+2.6.  Calculating the Premaster Secret
+
+   The premaster secret is calculated by the client as follows:
+
+        I, P = <read from user>
+        N, g, s, B = <read from server>
+        a = random()
+        A = g^a % N
+        u = SHA1(PAD(A) | PAD(B))
+        k = SHA1(N | PAD(g))
+        x = SHA1(s | SHA1(I | ":" | P))
+        <premaster secret> = (B - (k * g^x)) ^ (a + (u * x)) % N
+
+   The premaster secret is calculated by the server as follows:
+
+        N, g, s, v = <read from password file>
+        b = random()
+        k = SHA1(N | PAD(g))
+        B = k*v + g^b % N
+        A = <read from client>
+        u = SHA1(PAD(A) | PAD(B))
+        <premaster secret> = (A * v^u) ^ b % N
+
+   The finished messages perform the same function as the client and
+   server evidence messages (M1 and M2) specified in [SRP-RFC].  If
+   either the client or the server calculates an incorrect premaster
+   secret, the finished messages will fail to decrypt properly, and the
+   other party will return a "bad_record_mac" alert.
+
+   If a client application receives a "bad_record_mac" alert when
+   performing an SRP handshake, it should inform the user that the
+   entered user name and password are incorrect.
+
+
+
+Taylor, et al.               Informational                      [Page 8]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+2.7.  Ciphersuite Definitions
+
+   The following cipher suites are added by this document.  The usage of
+   Advanced Encryption Standard (AES) cipher suites is as defined in
+   [AESCIPH].
+
+      CipherSuite TLS_SRP_SHA_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1A };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1B };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1C };
+
+      CipherSuite TLS_SRP_SHA_WITH_AES_128_CBC_SHA = { 0xC0,0x1D };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_AES_128_CBC_SHA = { 0xC0,0x1E };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_AES_128_CBC_SHA = { 0xC0,0x1F };
+
+      CipherSuite TLS_SRP_SHA_WITH_AES_256_CBC_SHA = { 0xC0,0x20 };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_AES_256_CBC_SHA = { 0xC0,0x21 };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_AES_256_CBC_SHA = { 0xC0,0x22 };
+
+   Cipher suites that begin with TLS_SRP_SHA_RSA or TLS_SRP_SHA_DSS
+   require the server to send a certificate message containing a
+   certificate with the specified type of public key, and to sign the
+   server key exchange message using a matching private key.
+
+   Cipher suites that do not include a digital signature algorithm
+   identifier assume that the server is authenticated by its possession
+   of the SRP verifier.
+
+   Implementations conforming to this specification MUST implement the
+   TLS_SRP_SHA_WITH_3DES_EDE_CBC_SHA cipher suite, SHOULD implement the
+   TLS_SRP_SHA_WITH_AES_128_CBC_SHA and TLS_SRP_SHA_WITH_AES_256_CBC_SHA
+   cipher suites, and MAY implement the remaining cipher suites.
+
+2.8.  New Message Structures
+
+   This section shows the structure of the messages passed during a
+   handshake that uses SRP for authentication.  The representation
+   language used is the same as that used in [TLS].
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                      [Page 9]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+2.8.1.  Client Hello
+
+   A new extension "srp", with value 12, has been added to the
+   enumerated ExtensionType defined in [TLSEXT].  This value MUST be
+   used as the extension number for the SRP extension.
+
+   The "extension_data" field of the SRP extension SHALL contain:
+
+        opaque srp_I<1..2^8-1>;
+
+   where srp_I is the user name, encoded per Section 2.3.
+
+2.8.2.  Server Key Exchange
+
+   A new value, "srp", has been added to the enumerated
+   KeyExchangeAlgorithm originally defined in [TLS].
+
+   When the value of KeyExchangeAlgorithm is set to "srp", the server's
+   SRP parameters are sent in the server key exchange message, encoded
+   in a ServerSRPParams structure.
+
+   If a certificate is sent to the client, the server key exchange
+   message must be signed.
+
+        enum { rsa, diffie_hellman, srp } KeyExchangeAlgorithm;
+
+        struct {
+           select (KeyExchangeAlgorithm) {
+              case diffie_hellman:
+                 ServerDHParams params;
+                 Signature signed_params;
+              case rsa:
+                 ServerRSAParams params;
+                 Signature signed_params;
+              case srp:   /* new entry */
+                 ServerSRPParams params;
+                 Signature signed_params;
+           };
+        } ServerKeyExchange;
+
+        struct {
+           opaque srp_N<1..2^16-1>;
+           opaque srp_g<1..2^16-1>;
+           opaque srp_s<1..2^8-1>;
+           opaque srp_B<1..2^16-1>;
+        } ServerSRPParams;     /* SRP parameters */
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 10]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+2.8.3.  Client Key Exchange
+
+   When the value of KeyExchangeAlgorithm is set to "srp", the client's
+   public value (A) is sent in the client key exchange message, encoded
+   in a ClientSRPPublic structure.
+
+        struct {
+           select (KeyExchangeAlgorithm) {
+              case rsa: EncryptedPreMasterSecret;
+              case diffie_hellman: ClientDiffieHellmanPublic;
+              case srp: ClientSRPPublic;   /* new entry */
+           } exchange_keys;
+        } ClientKeyExchange;
+
+        struct {
+           opaque srp_A<1..2^16-1>;
+        } ClientSRPPublic;
+
+2.9.  Error Alerts
+
+   This document introduces four new uses of alerts:
+
+   o  "unknown_psk_identity" (115) - this alert MAY be sent by a server
+      that would like to select an offered SRP cipher suite, if the SRP
+      extension is absent from the client's hello message.  This alert
+      is always fatal.  See Section 2.5.1.2 for details.
+
+   o  "unknown_psk_identity" (115) - this alert MAY be sent by a server
+      that receives an unknown user name.  This alert is always fatal.
+      See Section 2.5.1.3 for details.
+
+   o  "insufficient_security" (71) - this alert MUST be sent by a client
+      that receives unknown or untrusted (N, g) values.  This alert is
+      always fatal.  See Section 2.5.3 for details.
+
+   o  "illegal_parameter" (47) - this alert MUST be sent by a client or
+      server that receives a key exchange message with A % N = 0 or B %
+      N = 0.  This alert is always fatal.  See Section 2.5.3 and
+      Section 2.5.4 and for details.
+
+   The "insufficient_security" and "illegal_parameter" alerts are
+   defined in [TLS].  The "unknown_psk_identity" alert is defined in
+   [PSK].
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 11]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+3.  Security Considerations
+
+3.1.  General Considerations for Implementors
+
+   The checks described in Section 2.5.3 and Section 2.5.4 on the
+   received values for A and B are CRUCIAL for security and MUST be
+   performed.
+
+   The private values a and b SHOULD be at least 256-bit random numbers,
+   to give approximately 128 bits of security against certain methods of
+   calculating discrete logarithms.  See [TLS], Section D.1, for advice
+   on choosing cryptographically secure random numbers.
+
+3.2.  Accepting Group Parameters
+
+   An attacker who could calculate discrete logarithms % N could
+   compromise user passwords, and could also compromise the
+   confidentiality and integrity of TLS sessions.  Clients MUST ensure
+   that the received parameter N is large enough to make calculating
+   discrete logarithms computationally infeasible.
+
+   An attacker may try to send a prime value N that is large enough to
+   be secure, but that has a special form for which the attacker can
+   more easily compute discrete logarithms (e.g., using the algorithm
+   discussed in [TRAPDOOR]).  If the client executes the protocol using
+   such a prime, the client's password could be compromised.  Because of
+   the difficulty of checking for such primes in real time, clients
+   SHOULD only accept group parameters that come from a trusted source,
+   such as those listed in Appendix A, or parameters configured locally
+   by a trusted administrator.
+
+3.3.  Protocol Characteristics
+
+   If an attacker learns a user's SRP verifier (e.g., by gaining access
+   to a server's password file), the attacker can masquerade as the real
+   server to that user, and can also attempt a dictionary attack to
+   recover that user's password.
+
+   An attacker could repeatedly contact an SRP server and try to guess a
+   legitimate user's password.  Servers SHOULD take steps to prevent
+   this, such as limiting the rate of authentication attempts from a
+   particular IP address or against a particular user name.
+
+   The client's user name is sent in the clear in the Client Hello
+   message.  To avoid sending the user name in the clear, the client
+   could first open a conventional anonymous or server-authenticated
+   connection, then renegotiate an SRP-authenticated connection with the
+   handshake protected by the first connection.
+
+
+
+Taylor, et al.               Informational                     [Page 12]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   If the client receives an "unknown_psk_identity" alert in response to
+   a client hello, this alert may have been inserted by an attacker.
+   The client should be careful about making any decisions, or forming
+   any conclusions, based on receiving this alert.
+
+   It is possible to choose a (user name, password) pair such that the
+   resulting verifier will also match other, related, (user name,
+   password) pairs.  Thus, anyone using verifiers should be careful not
+   to assume that only a single (user name, password) pair matches the
+   verifier.
+
+3.4.  Hash Function Considerations
+
+   This protocol uses SHA-1 to derive several values:
+
+   o  u prevents an attacker who learns a user's verifier from being
+      able to authenticate as that user (see [SRP-6]).
+
+   o  k prevents an attacker who can select group parameters from being
+      able to launch a 2-for-1 guessing attack (see [SRP-6]).
+
+   o  x contains the user's password mixed with a salt.
+
+   Cryptanalytic attacks against SHA-1 that only affect its collision-
+   resistance do not compromise these uses.  If attacks against SHA-1
+   are discovered that do compromise these uses, new cipher suites
+   should be specified to use a different hash algorithm.
+
+   In this situation, clients could send a Client Hello message
+   containing new and/or old SRP cipher suites along with a single SRP
+   extension.  The server could then select the appropriate cipher suite
+   based on the type of verifier it has stored for this user.
+
+4.  IANA Considerations
+
+   This document defines a new TLS extension "srp" (value 12), whose
+   value has been assigned from the TLS ExtensionType Registry defined
+   in [TLSEXT].
+
+   This document defines nine new cipher suites, whose values have been
+   assigned from the TLS Ciphersuite registry defined in [TLS].
+
+      CipherSuite TLS_SRP_SHA_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1A };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1B };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_3DES_EDE_CBC_SHA = { 0xC0,0x1C };
+
+
+
+
+Taylor, et al.               Informational                     [Page 13]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+      CipherSuite TLS_SRP_SHA_WITH_AES_128_CBC_SHA = { 0xC0,0x1D };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_AES_128_CBC_SHA = { 0xC0,0x1E };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_AES_128_CBC_SHA = { 0xC0,0x1F };
+
+      CipherSuite TLS_SRP_SHA_WITH_AES_256_CBC_SHA = { 0xC0,0x20 };
+
+      CipherSuite TLS_SRP_SHA_RSA_WITH_AES_256_CBC_SHA = { 0xC0,0x21 };
+
+      CipherSuite TLS_SRP_SHA_DSS_WITH_AES_256_CBC_SHA = { 0xC0,0x22 };
+
+5.  References
+
+5.1.  Normative References
+
+   [REQ]         Bradner, S., "Key words for use in RFCs to Indicate
+                 Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [TLS]         Dierks, T. and E. Rescorla, "The TLS Protocol version
+                 1.1", RFC 4346, April 2006.
+
+   [TLSEXT]      Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
+                 J., and T. Wright, "Transport Layer Security (TLS)
+                 Extensions", RFC 4366, April 2006.
+
+   [STRINGPREP]  Hoffman, P. and M. Blanchet, "Preparation of
+                 Internationalized Strings ("stringprep")", RFC 3454,
+                 December 2002.
+
+   [SASLPREP]    Zeilenga, K., "SASLprep: Stringprep profile for user
+                 names and passwords", RFC 4013, February 2005.
+
+   [SRP-RFC]     Wu, T., "The SRP Authentication and Key Exchange
+                 System", RFC 2945, September 2000.
+
+   [SHA1]        "Secure Hash Standard (SHS)", FIPS 180-2, August 2002.
+
+   [HMAC]        Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
+                 Keyed-Hashing for Message Authentication", RFC 2104,
+                 February 1997.
+
+   [AESCIPH]     Chown, P., "Advanced Encryption Standard (AES)
+                 Ciphersuites for Transport Layer Security (TLS)",
+                 RFC 3268, June 2002.
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 14]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   [PSK]         Eronen, P. and H. Tschofenig, "Pre-Shared Key
+                 Ciphersuites for Transport Layer Security (TLS)",
+                 RFC 4279, December 2005.
+
+   [MODP]        Kivinen, T. and M. Kojo, "More Modular Exponentiation
+                 (MODP) Diffie-Hellman groups for Internet Key Exchange
+                 (IKE)", RFC 3526, May 2003.
+
+5.2.  Informative References
+
+   [IMAP]        Newman, C., "Using TLS with IMAP, POP3 and ACAP",
+                 RFC 2595, June 1999.
+
+   [SRP-6]       Wu, T., "SRP-6: Improvements and Refinements to the
+                 Secure Remote Password Protocol", Submission to IEEE
+                 P1363.2 working group, October 2002,
+                 <http://grouper.ieee.org/groups/1363/>.
+
+   [SRP]         Wu, T., "The Secure Remote Password Protocol",
+                 Proceedings of the 1998 Internet Society Network and
+                 Distributed System Security Symposium pp. 97-111,
+                 March 1998.
+
+   [TRAPDOOR]    Gordon, D., "Designing and Detecting Trapdoors for
+                 Discrete Log Cryptosystems", Springer-Verlag Advances
+                 in Cryptology - Crypto '92, pp. 66-75, 1993.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 15]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+Appendix A.  SRP Group Parameters
+
+   The 1024-, 1536-, and 2048-bit groups are taken from software
+   developed by Tom Wu and Eugene Jhong for the Stanford SRP
+   distribution, and subsequently proven to be prime.  The larger primes
+   are taken from [MODP], but generators have been calculated that are
+   primitive roots of N, unlike the generators in [MODP].
+
+   The 1024-bit and 1536-bit groups MUST be supported.
+
+   1.  1024-bit Group
+
+       The hexadecimal value for the prime is:
+
+          EEAF0AB9 ADB38DD6 9C33F80A FA8FC5E8 60726187 75FF3C0B 9EA2314C
+          9C256576 D674DF74 96EA81D3 383B4813 D692C6E0 E0D5D8E2 50B98BE4
+          8E495C1D 6089DAD1 5DC7D7B4 6154D6B6 CE8EF4AD 69B15D49 82559B29
+          7BCF1885 C529F566 660E57EC 68EDBC3C 05726CC0 2FD4CBF4 976EAA9A
+          FD5138FE 8376435B 9FC61D2F C0EB06E3
+
+       The generator is: 2.
+
+   2.  1536-bit Group
+
+       The hexadecimal value for the prime is:
+
+          9DEF3CAF B939277A B1F12A86 17A47BBB DBA51DF4 99AC4C80 BEEEA961
+          4B19CC4D 5F4F5F55 6E27CBDE 51C6A94B E4607A29 1558903B A0D0F843
+          80B655BB 9A22E8DC DF028A7C EC67F0D0 8134B1C8 B9798914 9B609E0B
+          E3BAB63D 47548381 DBC5B1FC 764E3F4B 53DD9DA1 158BFD3E 2B9C8CF5
+          6EDF0195 39349627 DB2FD53D 24B7C486 65772E43 7D6C7F8C E442734A
+          F7CCB7AE 837C264A E3A9BEB8 7F8A2FE9 B8B5292E 5A021FFF 5E91479E
+          8CE7A28C 2442C6F3 15180F93 499A234D CF76E3FE D135F9BB
+
+       The generator is: 2.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 16]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   3.  2048-bit Group
+
+       The hexadecimal value for the prime is:
+
+          AC6BDB41 324A9A9B F166DE5E 1389582F AF72B665 1987EE07 FC319294
+          3DB56050 A37329CB B4A099ED 8193E075 7767A13D D52312AB 4B03310D
+          CD7F48A9 DA04FD50 E8083969 EDB767B0 CF609517 9A163AB3 661A05FB
+          D5FAAAE8 2918A996 2F0B93B8 55F97993 EC975EEA A80D740A DBF4FF74
+          7359D041 D5C33EA7 1D281E44 6B14773B CA97B43A 23FB8016 76BD207A
+          436C6481 F1D2B907 8717461A 5B9D32E6 88F87748 544523B5 24B0D57D
+          5EA77A27 75D2ECFA 032CFBDB F52FB378 61602790 04E57AE6 AF874E73
+          03CE5329 9CCC041C 7BC308D8 2A5698F3 A8D0C382 71AE35F8 E9DBFBB6
+          94B5C803 D89F7AE4 35DE236D 525F5475 9B65E372 FCD68EF2 0FA7111F
+          9E4AFF73
+
+       The generator is: 2.
+
+   4.  3072-bit Group
+
+       This prime is: 2^3072 - 2^3008 - 1 + 2^64 * { [2^2942 pi] +
+       1690314 }
+
+       Its hexadecimal value is:
+
+          FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+          8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+          302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+          A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
+          49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8
+          FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+          670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C
+          180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718
+          3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AAAC42D AD33170D
+          04507A33 A85521AB DF1CBA64 ECFB8504 58DBEF0A 8AEA7157 5D060C7D
+          B3970F85 A6E1E4C7 ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226
+          1AD2EE6B F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
+          BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31 43DB5BFC
+          E0FD108E 4B82D120 A93AD2CA FFFFFFFF FFFFFFFF
+
+       The generator is: 5.
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 17]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   5.  4096-bit Group
+
+       This prime is: 2^4096 - 2^4032 - 1 + 2^64 * { [2^3966 pi] +
+       240904 }
+
+       Its hexadecimal value is:
+
+          FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+          8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+          302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+          A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
+          49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8
+          FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+          670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C
+          180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718
+          3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AAAC42D AD33170D
+          04507A33 A85521AB DF1CBA64 ECFB8504 58DBEF0A 8AEA7157 5D060C7D
+          B3970F85 A6E1E4C7 ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226
+          1AD2EE6B F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
+          BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31 43DB5BFC
+          E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7 88719A10 BDBA5B26
+          99C32718 6AF4E23C 1A946834 B6150BDA 2583E9CA 2AD44CE8 DBBBC2DB
+          04DE8EF9 2E8EFC14 1FBECAA6 287C5947 4E6BC05D 99B2964F A090C3A2
+          233BA186 515BE7ED 1F612970 CEE2D7AF B81BDD76 2170481C D0069127
+          D5B05AA9 93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34063199
+          FFFFFFFF FFFFFFFF
+
+       The generator is: 5.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 18]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   6.  6144-bit Group
+
+       This prime is: 2^6144 - 2^6080 - 1 + 2^64 * { [2^6014 pi] +
+       929484 }
+
+       Its hexadecimal value is:
+
+          FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+          8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+          302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+          A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
+          49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8
+          FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+          670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C
+          180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718
+          3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AAAC42D AD33170D
+          04507A33 A85521AB DF1CBA64 ECFB8504 58DBEF0A 8AEA7157 5D060C7D
+          B3970F85 A6E1E4C7 ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226
+          1AD2EE6B F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
+          BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31 43DB5BFC
+          E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7 88719A10 BDBA5B26
+          99C32718 6AF4E23C 1A946834 B6150BDA 2583E9CA 2AD44CE8 DBBBC2DB
+          04DE8EF9 2E8EFC14 1FBECAA6 287C5947 4E6BC05D 99B2964F A090C3A2
+          233BA186 515BE7ED 1F612970 CEE2D7AF B81BDD76 2170481C D0069127
+          D5B05AA9 93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34028492
+          36C3FAB4 D27C7026 C1D4DCB2 602646DE C9751E76 3DBA37BD F8FF9406
+          AD9E530E E5DB382F 413001AE B06A53ED 9027D831 179727B0 865A8918
+          DA3EDBEB CF9B14ED 44CE6CBA CED4BB1B DB7F1447 E6CC254B 33205151
+          2BD7AF42 6FB8F401 378CD2BF 5983CA01 C64B92EC F032EA15 D1721D03
+          F482D7CE 6E74FEF6 D55E702F 46980C82 B5A84031 900B1C9E 59E7C97F
+          BEC7E8F3 23A97A7E 36CC88BE 0F1D45B7 FF585AC5 4BD407B2 2B4154AA
+          CC8F6D7E BF48E1D8 14CC5ED2 0F8037E0 A79715EE F29BE328 06A1D58B
+          B7C5DA76 F550AA3D 8A1FBFF0 EB19CCB1 A313D55C DA56C9EC 2EF29632
+          387FE8D7 6E3C0468 043E8F66 3F4860EE 12BF2D5B 0B7474D6 E694F91E
+          6DCC4024 FFFFFFFF FFFFFFFF
+
+       The generator is: 5.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 19]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+   7.  8192-bit Group
+
+       This prime is: 2^8192 - 2^8128 - 1 + 2^64 * { [2^8062 pi] +
+       4743158 }
+
+       Its hexadecimal value is:
+
+          FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+          8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+          302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+          A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
+          49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8
+          FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+          670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B E39E772C
+          180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9 DE2BCBF6 95581718
+          3995497C EA956AE5 15D22618 98FA0510 15728E5A 8AAAC42D AD33170D
+          04507A33 A85521AB DF1CBA64 ECFB8504 58DBEF0A 8AEA7157 5D060C7D
+          B3970F85 A6E1E4C7 ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226
+          1AD2EE6B F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
+          BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31 43DB5BFC
+          E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7 88719A10 BDBA5B26
+          99C32718 6AF4E23C 1A946834 B6150BDA 2583E9CA 2AD44CE8 DBBBC2DB
+          04DE8EF9 2E8EFC14 1FBECAA6 287C5947 4E6BC05D 99B2964F A090C3A2
+          233BA186 515BE7ED 1F612970 CEE2D7AF B81BDD76 2170481C D0069127
+          D5B05AA9 93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34028492
+          36C3FAB4 D27C7026 C1D4DCB2 602646DE C9751E76 3DBA37BD F8FF9406
+          AD9E530E E5DB382F 413001AE B06A53ED 9027D831 179727B0 865A8918
+          DA3EDBEB CF9B14ED 44CE6CBA CED4BB1B DB7F1447 E6CC254B 33205151
+          2BD7AF42 6FB8F401 378CD2BF 5983CA01 C64B92EC F032EA15 D1721D03
+          F482D7CE 6E74FEF6 D55E702F 46980C82 B5A84031 900B1C9E 59E7C97F
+          BEC7E8F3 23A97A7E 36CC88BE 0F1D45B7 FF585AC5 4BD407B2 2B4154AA
+          CC8F6D7E BF48E1D8 14CC5ED2 0F8037E0 A79715EE F29BE328 06A1D58B
+          B7C5DA76 F550AA3D 8A1FBFF0 EB19CCB1 A313D55C DA56C9EC 2EF29632
+          387FE8D7 6E3C0468 043E8F66 3F4860EE 12BF2D5B 0B7474D6 E694F91E
+          6DBE1159 74A3926F 12FEE5E4 38777CB6 A932DF8C D8BEC4D0 73B931BA
+          3BC832B6 8D9DD300 741FA7BF 8AFC47ED 2576F693 6BA42466 3AAB639C
+          5AE4F568 3423B474 2BF1C978 238F16CB E39D652D E3FDB8BE FC848AD9
+          22222E04 A4037C07 13EB57A8 1A23F0C7 3473FC64 6CEA306B 4BCBC886
+          2F8385DD FA9D4B7F A2C087E8 79683303 ED5BDD3A 062B3CF5 B3A278A6
+          6D2A13F8 3F44F82D DF310EE0 74AB6A36 4597E899 A0255DC1 64F31CC5
+          0846851D F9AB4819 5DED7EA1 B1D510BD 7EE74D73 FAF36BC3 1ECFA268
+          359046F4 EB879F92 4009438B 481C6CD7 889A002E D5EE382B C9190DA6
+          FC026E47 9558E447 5677E9AA 9E3050E2 765694DF C81F56E8 80B96E71
+          60C980DD 98EDD3DF FFFFFFFF FFFFFFFF
+
+       The generator is: 19 (decimal).
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 20]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+Appendix B.  SRP Test Vectors
+
+   The following test vectors demonstrate calculation of the verifier
+   and premaster secret.
+
+      I = "alice"
+
+      P = "password123"
+
+      s = BEB25379 D1A8581E B5A72767 3A2441EE
+
+      N, g = <1024-bit parameters from Appendix A>
+
+      k = 7556AA04 5AEF2CDD 07ABAF0F 665C3E81 8913186F
+
+      x = 94B7555A ABE9127C C58CCF49 93DB6CF8 4D16C124
+
+      v =
+
+         7E273DE8 696FFC4F 4E337D05 B4B375BE B0DDE156 9E8FA00A 9886D812
+         9BADA1F1 822223CA 1A605B53 0E379BA4 729FDC59 F105B478 7E5186F5
+         C671085A 1447B52A 48CF1970 B4FB6F84 00BBF4CE BFBB1681 52E08AB5
+         EA53D15C 1AFF87B2 B9DA6E04 E058AD51 CC72BFC9 033B564E 26480D78
+         E955A5E2 9E7AB245 DB2BE315 E2099AFB
+
+      a =
+
+         60975527 035CF2AD 1989806F 0407210B C81EDC04 E2762A56 AFD529DD
+         DA2D4393
+
+      b =
+
+         E487CB59 D31AC550 471E81F0 0F6928E0 1DDA08E9 74A004F4 9E61F5D1
+         05284D20
+
+      A =
+
+         61D5E490 F6F1B795 47B0704C 436F523D D0E560F0 C64115BB 72557EC4
+         4352E890 3211C046 92272D8B 2D1A5358 A2CF1B6E 0BFCF99F 921530EC
+         8E393561 79EAE45E 42BA92AE ACED8251 71E1E8B9 AF6D9C03 E1327F44
+         BE087EF0 6530E69F 66615261 EEF54073 CA11CF58 58F0EDFD FE15EFEA
+         B349EF5D 76988A36 72FAC47B 0769447B
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 21]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+      B =
+
+         BD0C6151 2C692C0C B6D041FA 01BB152D 4916A1E7 7AF46AE1 05393011
+         BAF38964 DC46A067 0DD125B9 5A981652 236F99D9 B681CBF8 7837EC99
+         6C6DA044 53728610 D0C6DDB5 8B318885 D7D82C7F 8DEB75CE 7BD4FBAA
+         37089E6F 9C6059F3 88838E7A 00030B33 1EB76840 910440B1 B27AAEAE
+         EB4012B7 D7665238 A8E3FB00 4B117B58
+
+      u =
+
+         CE38B959 3487DA98 554ED47D 70A7AE5F 462EF019
+
+      <premaster secret> =
+
+         B0DC82BA BCF30674 AE450C02 87745E79 90A3381F 63B387AA F271A10D
+         233861E3 59B48220 F7C4693C 9AE12B0A 6F67809F 0876E2D0 13800D6C
+         41BB59B6 D5979B5C 00A172B4 A2A5903A 0BDCAF8A 709585EB 2AFAFA8F
+         3499B200 210DCC1F 10EB3394 3CD67FC8 8A2F39A4 BE5BEC4E C0A3212D
+         C346D7E4 74B29EDE 8A469FFE CA686E5A
+
+Appendix C.  Acknowledgements
+
+   Thanks to all on the IETF TLS mailing list for ideas and analysis.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 22]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+Authors' Addresses
+
+   David Taylor
+   Independent
+
+   EMail: dtaylor@gnutls.org
+
+
+   Tom Wu
+   Cisco
+
+   EMail: thomwu@cisco.com
+
+
+   Nikos Mavrogiannopoulos
+   Independent
+
+   EMail: nmav@gnutls.org
+   URI:   http://www.gnutls.org/
+
+
+   Trevor Perrin
+   Independent
+
+   EMail: trevp@trevp.net
+   URI:   http://trevp.net/
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 23]
+
+RFC 5054            Using SRP for TLS Authentication       November 2007
+
+
+Full Copyright Statement
+
+   Copyright (C) The IETF Trust (2007).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 78, and except as set forth therein, the authors
+   retain all their rights.
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+
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+
+
+
+
+
+
+
+
+
+
+
+
+Taylor, et al.               Informational                     [Page 24]
+