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RFC 5246


The Transport Layer Security (TLS) Protocol Version 1.2

Part 4 of 5, p. 64 to 84
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8.  Cryptographic Computations

   In order to begin connection protection, the TLS Record Protocol
   requires specification of a suite of algorithms, a master secret, and
   the client and server random values.  The authentication, encryption,
   and MAC algorithms are determined by the cipher_suite selected by the
   server and revealed in the ServerHello 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

      master_secret = PRF(pre_master_secret, "master secret",
                          ClientHello.random + ServerHello.random)

   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

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

   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_AES_128_CBC_SHA (see Appendix A.5 for the

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

11.  Security Considerations

   Security issues are discussed throughout this memo, especially in
   Appendices D, E, and F.

12.  IANA Considerations

   This document uses several registries that were originally created in
   [TLS1.1].  IANA has updated these to reference this document.  The
   registries and their allocation policies (unchanged from [TLS1.1])
   are listed below.

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   -  TLS ClientCertificateType Identifiers Registry: Future values in
      the range 0-63 (decimal) inclusive are assigned via Standards
      Action [RFC2434].  Values in the range 64-223 (decimal) inclusive
      are assigned via Specification Required [RFC2434].  Values from
      224-255 (decimal) inclusive are reserved for Private Use

   -  TLS Cipher Suite Registry: Future values with the first byte in
      the range 0-191 (decimal) inclusive are assigned via Standards
      Action [RFC2434].  Values with the first byte in the range 192-254
      (decimal) are assigned via Specification Required [RFC2434].
      Values with the first byte 255 (decimal) are reserved for Private
      Use [RFC2434].

   -  This document defines several new HMAC-SHA256-based cipher suites,
      whose values (in Appendix A.5) have been allocated from the TLS
      Cipher Suite registry.

   -  TLS ContentType Registry: Future values are allocated via
      Standards Action [RFC2434].

   -  TLS Alert Registry: Future values are allocated via Standards
      Action [RFC2434].

   -  TLS HandshakeType Registry: Future values are allocated via
      Standards Action [RFC2434].

   This document also uses a registry originally created in [RFC4366].
   IANA has updated it to reference this document.  The registry and its
   allocation policy (unchanged from [RFC4366]) is listed below:

   -  TLS ExtensionType Registry: Future values are allocated via IETF
      Consensus [RFC2434].  IANA has updated this registry to include
      the signature_algorithms extension and its corresponding value
      (see Section

   In addition, this document defines two new registries to be
   maintained by IANA:

   -  TLS SignatureAlgorithm Registry: The registry has been initially
      populated with the values described in Section  Future
      values in the range 0-63 (decimal) inclusive are assigned via
      Standards Action [RFC2434].  Values in the range 64-223 (decimal)
      inclusive are assigned via Specification Required [RFC2434].
      Values from 224-255 (decimal) inclusive are reserved for Private
      Use [RFC2434].

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   -  TLS HashAlgorithm Registry: The registry has been initially
      populated with the values described in Section  Future
      values in the range 0-63 (decimal) inclusive are assigned via
      Standards Action [RFC2434].  Values in the range 64-223 (decimal)
      inclusive are assigned via Specification Required [RFC2434].
      Values from 224-255 (decimal) inclusive are reserved for Private
      Use [RFC2434].

      This document also uses the TLS Compression Method Identifiers
      Registry, defined in [RFC3749].  IANA has allocated value 0 for
      the "null" compression method.

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Appendix A.  Protocol Data Structures and Constant Values

   This section describes protocol types and constants.

A.1.  Record Layer

   struct {
       uint8 major;
       uint8 minor;
   } ProtocolVersion;

   ProtocolVersion version = { 3, 3 };     /* TLS v1.2*/

   enum {
       change_cipher_spec(20), alert(21), handshake(22),
       application_data(23), (255)
   } ContentType;

   struct {
       ContentType type;
       ProtocolVersion version;
       uint16 length;
       opaque fragment[TLSPlaintext.length];
   } TLSPlaintext;

   struct {
       ContentType type;
       ProtocolVersion version;
       uint16 length;
       opaque fragment[TLSCompressed.length];
   } TLSCompressed;

   struct {
       ContentType type;
       ProtocolVersion version;
       uint16 length;
       select (SecurityParameters.cipher_type) {
           case stream: GenericStreamCipher;
           case block:  GenericBlockCipher;
           case aead:   GenericAEADCipher;
       } fragment;
   } TLSCiphertext;

   stream-ciphered struct {
       opaque content[TLSCompressed.length];
       opaque MAC[SecurityParameters.mac_length];
   } GenericStreamCipher;

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   struct {
       opaque IV[SecurityParameters.record_iv_length];
       block-ciphered struct {
           opaque content[TLSCompressed.length];
           opaque MAC[SecurityParameters.mac_length];
           uint8 padding[GenericBlockCipher.padding_length];
           uint8 padding_length;
   } GenericBlockCipher;

   struct {
      opaque nonce_explicit[SecurityParameters.record_iv_length];
      aead-ciphered struct {
          opaque content[TLSCompressed.length];
   } GenericAEADCipher;

A.2.  Change Cipher Specs Message

   struct {
       enum { change_cipher_spec(1), (255) } type;
   } ChangeCipherSpec;

A.3.  Alert Messages

   enum { warning(1), fatal(2), (255) } AlertLevel;

   enum {

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       unsupported_extension(110),           /* new */
   } AlertDescription;

   struct {
       AlertLevel level;
       AlertDescription description;
   } Alert;

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),
   } 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;

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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..2^16-2>;
       CompressionMethod compression_methods<1..2^8-1>;
       select (extensions_present) {
           case false:
               struct {};
           case true:
               Extension extensions<0..2^16-1>;
   } ClientHello;

   struct {
       ProtocolVersion server_version;
       Random random;
       SessionID session_id;
       CipherSuite cipher_suite;
       CompressionMethod compression_method;
       select (extensions_present) {
           case false:
               struct {};
           case true:
               Extension extensions<0..2^16-1>;
   } ServerHello;

   struct {
       ExtensionType extension_type;
       opaque extension_data<0..2^16-1>;
   } Extension;

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   enum {
       signature_algorithms(13), (65535)
   } ExtensionType;

       none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
       sha512(6), (255)
   } HashAlgorithm;
   enum {
      anonymous(0), rsa(1), dsa(2), ecdsa(3), (255)
   } SignatureAlgorithm;

   struct {
         HashAlgorithm hash;
         SignatureAlgorithm signature;
   } SignatureAndHashAlgorithm;


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 { dhe_dss, dhe_rsa, dh_anon, rsa,dh_dss, dh_rsa
          /* may be extended, e.g., for ECDH -- see [TLSECC] */
        } KeyExchangeAlgorithm;

   struct {
       opaque dh_p<1..2^16-1>;
       opaque dh_g<1..2^16-1>;
       opaque dh_Ys<1..2^16-1>;
   } ServerDHParams;     /* Ephemeral DH parameters */

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   struct {
       select (KeyExchangeAlgorithm) {
           case dh_anon:
               ServerDHParams params;
           case dhe_dss:
           case dhe_rsa:
               ServerDHParams params;
               digitally-signed struct {
                   opaque client_random[32];
                   opaque server_random[32];
                   ServerDHParams params;
               } signed_params;
           case rsa:
           case dh_dss:
           case dh_rsa:
               struct {} ;
              /* message is omitted for rsa, dh_dss, and dh_rsa */
           /* may be extended, e.g., for ECDH -- see [TLSECC] */
   } ServerKeyExchange;

   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),
   } 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;

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A.4.3.  Client Authentication and Key Exchange Messages

   struct {
       select (KeyExchangeAlgorithm) {
           case rsa:
           case dhe_dss:
           case dhe_rsa:
           case dh_dss:
           case dh_rsa:
           case dh_anon:
       } exchange_keys;
   } ClientKeyExchange;

   struct {
       ProtocolVersion client_version;
       opaque random[46];
   } PreMasterSecret;

   struct {
       public-key-encrypted PreMasterSecret pre_master_secret;
   } EncryptedPreMasterSecret;

   enum { implicit, explicit } PublicValueEncoding;

   struct {
       select (PublicValueEncoding) {
           case implicit: struct {};
           case explicit: opaque DH_Yc<1..2^16-1>;
       } dh_public;
   } ClientDiffieHellmanPublic;

   struct {
        digitally-signed struct {
            opaque handshake_messages[handshake_messages_length];
   } CertificateVerify;

A.4.4.  Handshake Finalization Message

   struct {
       opaque verify_data[verify_data_length];
   } Finished;

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A.5.  The Cipher Suite

   The following values define the cipher suite codes used in the
   ClientHello and ServerHello messages.

   A cipher suite defines a cipher specification supported in TLS
   Version 1.2.

   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 any signature-capable certificate in the certificate request

      CipherSuite TLS_RSA_WITH_NULL_MD5                 = { 0x00,0x01 };
      CipherSuite TLS_RSA_WITH_NULL_SHA                 = { 0x00,0x02 };
      CipherSuite TLS_RSA_WITH_NULL_SHA256              = { 0x00,0x3B };
      CipherSuite TLS_RSA_WITH_RC4_128_MD5              = { 0x00,0x04 };
      CipherSuite TLS_RSA_WITH_RC4_128_SHA              = { 0x00,0x05 };
      CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA         = { 0x00,0x0A };
      CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA          = { 0x00,0x2F };
      CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA          = { 0x00,0x35 };
      CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA256       = { 0x00,0x3C };
      CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA256       = { 0x00,0x3D };

   The following cipher suite 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 signature-capable certificate, which has
   been signed by the CA.  The signing algorithm used by the server is
   specified after the DHE component of the CipherSuite name.  The
   server can request any 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

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      CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA      = { 0x00,0x0D };
      CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA      = { 0x00,0x10 };
      CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA     = { 0x00,0x13 };
      CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA     = { 0x00,0x16 };
      CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA       = { 0x00,0x30 };
      CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA       = { 0x00,0x31 };
      CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA      = { 0x00,0x32 };
      CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA      = { 0x00,0x33 };
      CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA       = { 0x00,0x36 };
      CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA       = { 0x00,0x37 };
      CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA      = { 0x00,0x38 };
      CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA      = { 0x00,0x39 };
      CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA256    = { 0x00,0x3E };
      CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA256    = { 0x00,0x3F };
      CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA256   = { 0x00,0x40 };
      CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA256   = { 0x00,0x67 };
      CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA256    = { 0x00,0x68 };
      CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA256    = { 0x00,0x69 };
      CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA256   = { 0x00,0x6A };
      CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA256   = { 0x00,0x6B };

   The following cipher suites are used for completely anonymous
   Diffie-Hellman communications in which neither party is
   authenticated.  Note that this mode is vulnerable to man-in-the-
   middle attacks.  Using this mode therefore is of limited use: These
   cipher suites MUST NOT be used by TLS 1.2 implementations unless the
   application layer has specifically requested to allow anonymous key
   exchange.  (Anonymous key exchange may sometimes be acceptable, for
   example, to support opportunistic encryption when no set-up for
   authentication is in place, or when TLS is used as part of more
   complex security protocols that have other means to ensure

      CipherSuite TLS_DH_anon_WITH_RC4_128_MD5          = { 0x00,0x18 };
      CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA     = { 0x00,0x1B };
      CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA      = { 0x00,0x34 };
      CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA      = { 0x00,0x3A };
      CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA256   = { 0x00,0x6C };
      CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA256   = { 0x00,0x6D };

   Note that using non-anonymous key exchange without actually verifying
   the key exchange is essentially equivalent to anonymous key exchange,
   and the same precautions apply.  While non-anonymous key exchange
   will generally involve a higher computational and communicational
   cost than anonymous key exchange, it may be in the interest of
   interoperability not to disable non-anonymous key exchange when the
   application layer is allowing anonymous key exchange.

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   New cipher suite values have been assigned by IANA as described in
   Section 12.

   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 { tls_prf_sha256 } PRFAlgorithm;

   enum { null, rc4, 3des, aes } BulkCipherAlgorithm;

   enum { stream, block, aead } CipherType;

   enum { null, hmac_md5, hmac_sha1, hmac_sha256, hmac_sha384,
     hmac_sha512} MACAlgorithm;

   /* Other values may be added to the algorithms specified in
   CompressionMethod, PRFAlgorithm, BulkCipherAlgorithm, and
   MACAlgorithm. */

   struct {
       ConnectionEnd          entity;
       PRFAlgorithm           prf_algorithm;
       BulkCipherAlgorithm    bulk_cipher_algorithm;
       CipherType             cipher_type;
       uint8                  enc_key_length;
       uint8                  block_length;
       uint8                  fixed_iv_length;
       uint8                  record_iv_length;
       MACAlgorithm           mac_algorithm;
       uint8                  mac_length;
       uint8                  mac_key_length;
       CompressionMethod      compression_algorithm;
       opaque                 master_secret[48];
       opaque                 client_random[32];
       opaque                 server_random[32];
   } SecurityParameters;

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A.7.  Changes to RFC 4492

   RFC 4492 [TLSECC] adds Elliptic Curve cipher suites to TLS.  This
   document changes some of the structures used in that document.  This
   section details the required changes for implementors of both RFC
   4492 and TLS 1.2.  Implementors of TLS 1.2 who are not implementing
   RFC 4492 do not need to read this section.

   This document adds a "signature_algorithm" field to the digitally-
   signed element in order to identify the signature and digest
   algorithms used to create a signature.  This change applies to
   digital signatures formed using ECDSA as well, thus allowing ECDSA
   signatures to be used with digest algorithms other than SHA-1,
   provided such use is compatible with the certificate and any
   restrictions imposed by future revisions of [PKIX].

   As described in Sections 7.4.2 and 7.4.6, the restrictions on the
   signature algorithms used to sign certificates are no longer tied to
   the cipher suite (when used by the server) or the
   ClientCertificateType (when used by the client).  Thus, the
   restrictions on the algorithm used to sign certificates specified in
   Sections 2 and 3 of RFC 4492 are also relaxed.  As in this document,
   the restrictions on the keys in the end-entity certificate remain.

Appendix B.  Glossary

   Advanced Encryption Standard (AES)
      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.  TLS currently only supports the 128- and 256-bit key

   application protocol
      An application protocol is a protocol that normally layers
      directly on top of the transport layer (e.g., TCP/IP).  Examples
      include HTTP, TELNET, FTP, and SMTP.

   asymmetric cipher
      See public key cryptography.

   authenticated encryption with additional data (AEAD)
      A symmetric encryption algorithm that simultaneously provides
      confidentiality and message integrity.

      Authentication is the ability of one entity to determine the
      identity of another entity.

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   block cipher
      A block cipher is an algorithm that operates on plaintext in
      groups of bits, called blocks.  64 bits was, and 128 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).

      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.

      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
      generally authenticated, while the client is only optionally

   client write key
      The key used to encrypt data written by the client.

   client write MAC key
      The secret data used to authenticate data written by the client.

      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 [DES] still is a very widely used symmetric encryption
      algorithm although it is considered as rather weak now.  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

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      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 [3DES] 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.

   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 186-2, "Digital Signature
      Standard", published January 2000 by the U.S. Department of
      Commerce [DSS].  A significant update [DSS-3] has been drafted and
      was published in March 2006.

   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

   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 hashing function that converts an arbitrarily long
      data stream into a hash of fixed size (16 bytes).  Due to
      significant progress in cryptanalysis, at the time of publication
      of this document, MD5 no longer can be considered a 'secure'
      hashing function.

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   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.

      A stream cipher invented by Ron Rivest.  A compatible cipher is
      described in [SCH].

      A very widely used public key algorithm that can be used for
      either encryption or digital signing.  [RSA]

      The server is the application entity that responds to requests for
      connections from clients.  See also "client".

      A TLS session is an association between a client and a server.
      Sessions are created by the handshake protocol.  Sessions define a
      set of cryptographic security parameters that can be shared among
      multiple connections.  Sessions are used to avoid the expensive
      negotiation of new security parameters for each connection.

   session identifier
      A session identifier is a value generated by a server that
      identifies a particular session.

   server write key
      The key used to encrypt data written by the server.

   server write MAC key
      The secret data used to authenticate data written by the server.

      The Secure Hash Algorithm [SHS] is defined in FIPS PUB 180-2.  It
      produces a 20-byte output.  Note that all references to SHA
      (without a numerical suffix) actually use the modified SHA-1

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      The 256-bit Secure Hash Algorithm is defined in FIPS PUB 180-2.
      It produces a 32-byte output.

      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 "Working Group
      Information" at the end of this document (see page 99).

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Appendix C.  Cipher Suite Definitions

Cipher Suite                            Key        Cipher         Mac

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_NULL_SHA256                RSA          NULL         SHA256
TLS_RSA_WITH_RC4_128_MD5                RSA          RC4_128      MD5
TLS_RSA_WITH_RC4_128_SHA                RSA          RC4_128      SHA
TLS_RSA_WITH_AES_128_CBC_SHA            RSA          AES_128_CBC  SHA
TLS_RSA_WITH_AES_256_CBC_SHA            RSA          AES_256_CBC  SHA
TLS_RSA_WITH_AES_128_CBC_SHA256         RSA          AES_128_CBC  SHA256
TLS_RSA_WITH_AES_256_CBC_SHA256         RSA          AES_256_CBC  SHA256
TLS_DH_anon_WITH_RC4_128_MD5            DH_anon      RC4_128      MD5
TLS_DH_anon_WITH_AES_128_CBC_SHA        DH_anon      AES_128_CBC  SHA
TLS_DH_anon_WITH_AES_256_CBC_SHA        DH_anon      AES_256_CBC  SHA
TLS_DH_DSS_WITH_AES_128_CBC_SHA256      DH_DSS       AES_128_CBC  SHA256
TLS_DH_RSA_WITH_AES_128_CBC_SHA256      DH_RSA       AES_128_CBC  SHA256
TLS_DH_anon_WITH_AES_128_CBC_SHA256     DH_anon      AES_128_CBC  SHA256
TLS_DH_DSS_WITH_AES_256_CBC_SHA256      DH_DSS       AES_256_CBC  SHA256
TLS_DH_RSA_WITH_AES_256_CBC_SHA256      DH_RSA       AES_256_CBC  SHA256
TLS_DH_anon_WITH_AES_256_CBC_SHA256     DH_anon      AES_256_CBC  SHA256

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                        Key      IV   Block
Cipher        Type    Material  Size  Size
------------  ------  --------  ----  -----
NULL          Stream      0       0    N/A
RC4_128       Stream     16       0    N/A
3DES_EDE_CBC  Block      24       8      8
AES_128_CBC   Block      16      16     16
AES_256_CBC   Block      32      16     16

MAC       Algorithm    mac_length  mac_key_length
--------  -----------  ----------  --------------
NULL      N/A              0             0
MD5       HMAC-MD5        16            16
SHA       HMAC-SHA1       20            20
SHA256    HMAC-SHA256     32            32

      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.

   IV Size
      The amount of data needed to be generated for the initialization
      vector.  Zero for stream ciphers; equal to the block size for
      block ciphers (this is equal to

   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.

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