Transport Layer Security over Stream Control Transmission Protocol
RFC 3436

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Network Working Group                                       A. Jungmaier
Request for Comments: 3436                           University of Essen
Category: Standards Track                                    E. Rescorla
                                                               RTFM Inc.
                                                               M. Tuexen
                                                              Siemens AG
                                                           December 2002

                     Transport Layer Security over
                  Stream Control Transmission Protocol

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 (2002).  All Rights Reserved.

Abstract

   This document describes the usage of the Transport Layer Security
   (TLS) protocol, as defined in RFC 2246, over the Stream Control
   Transmission Protocol (SCTP), as defined in RFC 2960 and RFC 3309.

   The user of TLS can take advantage of the features provided by SCTP,
   namely the support of multiple streams to avoid head of line blocking
   and the support of multi-homing to provide network level fault
   tolerance.

   Additionally, discussions of extensions of SCTP are also supported,
   meaning especially the support of dynamic reconfiguration of IP-
   addresses.

Jungmaier, et al.           Standards Track                     [Page 1]
RFC 3436                     TLS over SCTP                December 2002

1.  Introduction

1.1.  Overview

   This document describes the usage of the Transport Layer Security
   (TLS) protocol, as defined in [RFC2246], over the Stream Control
   Transmission Protocol (SCTP), as defined in [RFC2960] and [RFC3309].

   TLS is designed to run on top of a byte-stream oriented transport
   protocol providing a reliable, in-sequence delivery.  Thus, TLS is
   currently mainly being used on top of the Transmission Control
   Protocol (TCP), as defined in [RFC793].

   Comparing TCP and SCTP, the latter provides additional features and
   this document shows how TLS should be used with SCTP to provide some
   of these additional features to the TLS user.

   This document defines:

   -   how to use the multiple streams feature of SCTP.

   -   how to handle the message oriented nature of SCTP.

   It should be noted that the TLS user can take advantage of the multi-
   homing support of SCTP.  The dynamic reconfiguration of IP-addresses,
   as currently being discussed, can also be used with the described
   solution.

   The method described in this document does not require any changes of
   TLS or SCTP.  It is only required that SCTP implementations support
   the optional feature of fragmentation of SCTP user messages.

1.2.  Terminology

   This document uses the following terms:

      Association:
         An SCTP association.

      Connection:
         A TLS connection.

      Session:
         A TLS session.

      Stream:
         A unidirectional stream of an SCTP association.  It is uniquely
         identified by a stream identifier.

Jungmaier, et al.           Standards Track                     [Page 2]
RFC 3436                     TLS over SCTP                December 2002

1.3.  Abbreviations

   MTU:  Maximum Transmission Unit

   SCTP: Stream Control Transmission Protocol

   TCP:  Transmission Control Protocol

   TLS:  Transport Layer Security

2.  Conventions

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL", in this document are to be interpreted as described in
   BCP 14, RFC 2119 [RFC2119].

3.  SCTP Requirements

3.1.  Number of Inbound and Outbound Streams

   An association between the endpoints A and Z provides n streams from
   A to Z and m streams from Z to A.

   A pair consisting of two streams with the same stream identifier is
   considered and used as one bi-directional stream.

   Thus an SCTP association can be considered as a set of min(n,m) bi-
   directional streams and (max(n,m) - min(n,m)) uni-directional
   streams.

3.2.  Fragmentation of User Messages

   To avoid the knowledge and handling of the MTU inside TLS, SCTP MUST
   provide fragmentation of user messages, which is an optional feature
   of [RFC2960].  Since SCTP is a message oriented protocol, it must be
   able to transmit all TLS records as SCTP user messages.  Thus the
   supported maximum length of SCTP user messages MUST be at least 2^14
   + 2048 + 5 = 18437 bytes, which is the maximum length of a
   TLSCiphertext, as defined in [RFC2246].

   Please note that an SCTP implementation might need to support the