The Transport Layer Security (TLS) Protocol Version 1.2
RFC 5246

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Network Working Group                                          T. Dierks
Request for Comments: 5246                                   Independent
Obsoletes: 3268, 4346, 4366                                  E. Rescorla
Updates: 4492                                                 RTFM, Inc.
Category: Standards Track                                    August 2008

              The Transport Layer Security (TLS) Protocol
                              Version 1.2

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document specifies Version 1.2 of the Transport Layer Security
   (TLS) protocol.  The TLS protocol provides communications security
   over the Internet.  The protocol allows client/server applications to
   communicate in a way that is designed to prevent eavesdropping,
   tampering, or message forgery.

Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Terminology ...................................5
      1.2. Major Differences from TLS 1.1 .............................5
   2. Goals ...........................................................6
   3. Goals of This Document ..........................................7
   4. Presentation Language ...........................................7
      4.1. Basic Block Size ...........................................7
      4.2. Miscellaneous ..............................................8
      4.3. Vectors ....................................................8
      4.4. Numbers ....................................................9
      4.5. Enumerateds ................................................9
      4.6. Constructed Types .........................................10
           4.6.1. Variants ...........................................10
      4.7. Cryptographic Attributes ..................................12
      4.8. Constants .................................................14
   5. HMAC and the Pseudorandom Function .............................14
   6. The TLS Record Protocol ........................................15
      6.1. Connection States .........................................16
      6.2. Record Layer ..............................................19
           6.2.1. Fragmentation ......................................19

Dierks & Rescorla           Standards Track                     [Page 1]
RFC 5246                          TLS                        August 2008

           6.2.2. Record Compression and Decompression ...............20
           6.2.3. Record Payload Protection ..........................21
                  6.2.3.1. Null or Standard Stream Cipher ............22
                  6.2.3.2. CBC Block Cipher ..........................22
                  6.2.3.3. AEAD Ciphers ..............................24
      6.3. Key Calculation ...........................................25
   7. The TLS Handshaking Protocols ..................................26
      7.1. Change Cipher Spec Protocol ...............................27
      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 ..............................42
                  7.4.1.4. Hello Extensions ..........................44
                           7.4.1.4.1. Signature Algorithms ...........45
           7.4.2. Server Certificate .................................47
           7.4.3. Server Key Exchange Message ........................50
           7.4.4. Certificate Request ................................53
           7.4.5. Server Hello Done ..................................55
           7.4.6. Client Certificate .................................55
           7.4.7. Client Key Exchange Message ........................57
                  7.4.7.1. RSA-Encrypted Premaster Secret Message ....58
                  7.4.7.2. Client Diffie-Hellman Public Value ........61
           7.4.8. Certificate Verify .................................62
           7.4.9. Finished ...........................................63
   8. Cryptographic Computations .....................................64
      8.1. Computing the Master Secret ...............................64