Datagram Transport Layer Security
RFC 4347

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• 05

Network Working Group                                        E. Rescorla
Request for Comments: 4347                                    RTFM, Inc.
Category: Standards Track                                    N. Modadugu
                                                     Stanford University
                                                              April 2006

                   Datagram Transport Layer Security

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.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document specifies Version 1.0 of the Datagram Transport Layer
   Security (DTLS) protocol.  The DTLS protocol provides communications
   privacy for datagram protocols.  The protocol allows client/server
   applications to communicate in a way that is designed to prevent
   eavesdropping, tampering, or message forgery.  The DTLS protocol is
   based on the Transport Layer Security (TLS) protocol and provides
   equivalent security guarantees.  Datagram semantics of the underlying
   transport are preserved by the DTLS protocol.

Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Terminology ...................................3
   2. Usage Model .....................................................3
   3. Overview of DTLS ................................................4
      3.1. Loss-Insensitive Messaging .................................4
      3.2. Providing Reliability for Handshake ........................4
           3.2.1. Packet Loss .........................................5
           3.2.2. Reordering ..........................................5
           3.2.3. Message Size ........................................5
      3.3. Replay Detection ...........................................6
   4. Differences from TLS ............................................6
      4.1. Record Layer ...............................................6
           4.1.1. Transport Layer Mapping .............................7

Rescorla & Modadugu         Standards Track                     [Page 1]
RFC 4347           Datagram Transport Layer Security          April 2006

                  4.1.1.1. PMTU Discovery .............................8
           4.1.2. Record Payload Protection ...........................9
                  4.1.2.1. MAC ........................................9
                  4.1.2.2. Null or Standard Stream Cipher .............9
                  4.1.2.3. Block Cipher ..............................10
                  4.1.2.4. New Cipher Suites .........................10
                  4.1.2.5. Anti-replay ...............................10
      4.2. The DTLS Handshake Protocol ...............................11
           4.2.1. Denial of Service Countermeasures ..................11
           4.2.2. Handshake Message Format ...........................13
           4.2.3. Message Fragmentation and Reassembly ...............15
           4.2.4. Timeout and Retransmission .........................15
                  4.2.4.1. Timer Values ..............................18
           4.2.5. ChangeCipherSpec ...................................19
           4.2.6. Finished Messages ..................................19
           4.2.7. Alert Messages .....................................19
      4.3. Summary of new syntax .....................................19
           4.3.1. Record Layer .......................................20
           4.3.2. Handshake Protocol .................................20
   5. Security Considerations ........................................21
   6. Acknowledgements ...............................................22
   7. IANA Considerations ............................................22
   8. References .....................................................22
      8.1. Normative References ......................................22
      8.2. Informative References ....................................23

1. Introduction

   TLS [TLS] is the most widely deployed protocol for securing network
   traffic.  It is widely used for protecting Web traffic and for e-mail
   protocols such as IMAP [IMAP] and POP [POP].  The primary advantage
   of TLS is that it provides a transparent connection-oriented channel.
   Thus, it is easy to secure an application protocol by inserting TLS
   between the application layer and the transport layer.  However, TLS
   must run over a reliable transport channel -- typically TCP [TCP].
   It therefore cannot be used to secure unreliable datagram traffic.

   However, over the past few years an increasing number of application