[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-tuexen-tsvwg-dtls-for-sctp) 00 01 02 03 04 05 06 RFC 6083

Network Working Group                                          M. Tuexen
Internet-Draft                                             R. Seggelmann
Intended status: Standards Track      Muenster Univ. of Applied Sciences
Expires: April 26, 2010                                      E. Rescorla
                                                              RTFM, Inc.
                                                        October 23, 2009


   Datagram Transport Layer Security for Stream Control Transmission
                                Protocol
                 draft-ietf-tsvwg-dtls-for-sctp-02.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 26, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.






Tuexen, et al.           Expires April 26, 2010                 [Page 1]

Internet-Draft                DTLS for SCTP                 October 2009


Abstract

   This document describes the usage of the Datagram Transport Layer
   Security (DTLS) protocol over the Stream Control Transmission
   Protocol (SCTP).

   The user of DTLS over SCTP can take advantage of most of the features
   provided by SCTP and its extensions, especially support of

   o  multi-homing to provide network level fault tolerance.

   o  dynamic reconfiguration of IPv4 and IPv6 addresses.

   o  multiple streams to avoid head of line blocking.

   o  unordered delivery.

   o  dynamic reconfiguration of streams.

   o  partially reliable data transfer.

   However, the DTLS maximum user message size limit of 2^14 bytes
   applies also to DTLS over SCTP.  Since DTLS over SCTP uses the SCTP-
   AUTH extension, the DTLS user can not manage the keying material,
   since this is done by the DTLS layer.


























Tuexen, et al.           Expires April 26, 2010                 [Page 2]

Internet-Draft                DTLS for SCTP                 October 2009


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   3.  DTLS Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   4.  SCTP Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9






































Tuexen, et al.           Expires April 26, 2010                 [Page 3]

Internet-Draft                DTLS for SCTP                 October 2009


1.  Introduction

1.1.  Overview

   This document describes the usage of the Datagram Transport Layer
   Security (DTLS) protocol, as defined in [I-D.ietf-tls-rfc4347-bis],
   over the Stream Control Transmission Protocol (SCTP), as defined in
   [RFC4960].

   TLS, from which DTLS was derived, 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 [RFC0793].

   TLS over SCTP as described in [RFC3436] has some serious limitations:

   o  It does not support the unordered delivery of SCTP user messages.

   o  It does not support partial reliability as defined in [RFC3758].

   o  It only supports the usage of the same number of streams in both
      directions.

   o  It uses a TLS connection for every bidirectional stream, which
      requires a substantial amount of resources and message exchanges
      if a large number of streams is used.

   DTLS over SCTP as described in this document overcomes these
   limitations of TLS over SCTP.  The user of DTLS over SCTP can use
   almost all services provided by SCTP and its partial reliability
   extension.  However, DTLS limits the user message size to 2^14 bytes.
   The dynamic modification of the IP-addresses used by the SCTP end-
   points is also supported.  The same applies to the dynamic
   reconfiguration of streams.  The DTLS user can request SCTP chunk
   types to be authenticated by using SCTP-AUTH as defined in [RFC4895].
   However, the DTLS user can not perform the SCTP-AUTH key management,
   because this is done by the DTLS layer.

   The method described in this document requires that the SCTP
   implementation supports the optional feature of fragmentation of SCTP
   user messages and the SCTP authentication extension defined in
   [RFC4895].

1.2.  Terminology

   This document uses the following terms:





Tuexen, et al.           Expires April 26, 2010                 [Page 4]

Internet-Draft                DTLS for SCTP                 October 2009


   Association:  An SCTP association.

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

1.3.  Abbreviations

   DTLS:  Datagram Transport Layer Security.

   MTU:  Maximum Transmission Unit.

   PPID:  Payload Protocol Identifier.

   SCTP:  Stream Control Transmission Protocol.

   TCP:  Transmission Control Protocol.

   TLS:  Transport Layer Security.


2.  Conventions

   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 [RFC2119].


3.  DTLS Considerations

3.1.  Message Sizes

   DTLS limits the DTLS user message size to the current Path MTU minus
   the header sizes.  This limit SHOULD be increased to 2^14 Bytes for
   DTLS over SCTP.

3.2.  Replay Detection

   Replay detection of DTLS MUST NOT be used.

3.3.  Path MTU Discovery

   Path MTU discovery of DTLS MUST NOT be used.

3.4.  Retransmission of Messages

   DTLS procedures for retransmissions MUST NOT be used.





Tuexen, et al.           Expires April 26, 2010                 [Page 5]

Internet-Draft                DTLS for SCTP                 October 2009


4.  SCTP Considerations

4.1.  Mapping of DTLS Records

   The supported maximum length of SCTP user messages MUST be at least
   2^14 + 2048 + 13 = 18445 bytes (2^14 + 2048 is the maximum length of
   the DTLSCiphertext.fragment and 13 is the size of the DTLS record
   header).  In particular, the SCTP implementation MUST support
   fragmentation of user messages.

   Every SCTP user message MUST consist of exactly one DTLS record.

4.2.  Payload Protocol Identifier Usage

   Application protocols running over DTLS over SCTP SHOULD register and
   use a separate payload protocol identifier (PPID) and SHOULD NOT
   reuse the PPID which they registered for running directly over SCTP.

   This means in particular that there is no specific PPID for DTLS.

4.3.  Stream Usage

   All DTLS messages of the ChangeCipherSpec, Alert, or Handshake
   protocol MUST be transported on stream 0 with unlimited reliability
   and with the ordered delivery feature.

   All DTLS messages of the ApplicationData protocol MAY be transported
   over stream 0 but users SHOULD use other streams to avoid possible
   performance problems due to head of line blocking.

4.4.  Chunk Handling

   The DATA, SACK, SHUTDOWN, and FORWARD-TSN chunks of SCTP MUST be sent
   in an authenticated way as described in [RFC4895].  Other chunks MAY
   be sent in an authenticated way.

   This makes sure that an attacker can not modify the stream a message
   is sent in or affect the ordered/unordered delivery of the message.
   It is also not possible for an attacker to drop messages and use
   forged FORWARD-TSN, SACK, and/or SHUTDOWN chunks to hide this
   dropping.

4.5.  Handshake

   A DTLS implementation discards DTLS messages from older epochs after
   some time as described in section 4.1 of [I-D.ietf-tls-rfc4347-bis].
   This is not acceptable when the DTLS user performs a reliable data
   transfer.  To avoid the discarding of messages, the following



Tuexen, et al.           Expires April 26, 2010                 [Page 6]

Internet-Draft                DTLS for SCTP                 October 2009


   procedures are required.

   Before sending a ChangeCipherSpec message all outstanding SCTP user
   messages MUST have been acknowledged by the SCTP peer and MUST NOT be
   revoked anymore by the SCTP peer.

   Prior to processing a received ChangeCipherSpec all other received
   SCTP user messages which are buffered in the SCTP layer MUST be read
   and processed by DTLS.

   User messages arriving between ChangeCipherSpec and Finished using
   the new epoch have probably passed the Finished and MUST be buffered
   by DTLS until the Finished is read.

4.6.  Handling of Endpoint-pair Shared Secrets

   The endpoint-pair shared secret for Shared Key Identifier 0 is empty.
   Whenever the master key changes, a 64 byte shared secret is derived
   from every master secret and provided as a new end-point pair shared
   secret by using the algorithm described in [I-D.ietf-tls-extractor].

   The Shared Key Identifier MUST be incremented by 1.  If it is 65535,
   the next value MUST be 1.

   Before sending the Finished message the active SCTP-AUTH key MUST be
   switched to the new one.

   Once the corresponding Finished message from the peer has been
   received the old SCTP-AUTH key SHOULD be removed.

4.7.  Shutdown

   To prevent DTLS from discarding DTLS user messages while shutting
   down, before sending a CloseNotify message all outstanding SCTP user
   messages MUST have been acknowledged by the SCTP peer and MUST NOT be
   revoked anymore by the SCTP peer.

   Prior to processing a received CloseNotify all other received SCTP
   user messages which are buffered in the SCTP layer MUST be read and
   processed by DTLS.


5.  IANA Considerations

   IANA needs to add a value to the TLS Exporter Label registry as
   described in [I-D.ietf-tls-extractor].  The label suggested is
   EXTRACTOR_DTLS_OVER_SCTP.  The reference should refer to this
   document.



Tuexen, et al.           Expires April 26, 2010                 [Page 7]

Internet-Draft                DTLS for SCTP                 October 2009


6.  Security Considerations

   The security considerations given in [I-D.ietf-tls-rfc4347-bis],
   [RFC4895], and [RFC4960] also apply to this document.

   It is possible to authenticate DTLS endpoints based on IP-addresses
   in certificates.  SCTP associations can use multiple addresses per
   SCTP endpoint.  Therefore it is possible that DTLS records will be
   sent from a different IP-address than that originally authenticated.
   This is not a problem provided that no security decisions are made
   based on that IP-address.  This is a special case of a general rule:
   all decisions should be based on the peer's authenticated identity,
   not on its transport layer identity.

   The SCTP user provides for each user message also a stream
   identifier, a flag whether the message is sent ordered or unordered
   and a payload protocol identifier.  Although DTLS can be used to
   provide privacy for the actual user message, none of these three are
   protected by DTLS.  They are sent as clear text, because they are
   part of the SCTP DATA chunk header.

   If future SCTP extensions define chunk types which processing affect
   the handling of TSNs, these chunk types MUST be sent in an
   authenticated way as described in [RFC4895].  One example would be an
   extension providing an alternate way of acknowledging TSNs.


7.  Acknowledgments

   The authors wish to thank Carsten Hohendorf, Alfred Hoenes, Daniel
   Mentz, Ian Goldberg, Anna Brunstrom, and Stefan Lindskog for their
   invaluable comments.


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758, May 2004.

   [RFC4895]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
              "Authenticated Chunks for the Stream Control Transmission
              Protocol (SCTP)", RFC 4895, August 2007.



Tuexen, et al.           Expires April 26, 2010                 [Page 8]

Internet-Draft                DTLS for SCTP                 October 2009


   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [I-D.ietf-tls-extractor]
              Rescorla, E., "Keying Material Exporters for Transport
              Layer Security (TLS)", draft-ietf-tls-extractor-07 (work
              in progress), September 2009.

   [I-D.ietf-tls-rfc4347-bis]
              Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security version 1.2", draft-ietf-tls-rfc4347-bis-03 (work
              in progress), October 2009.

8.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC3436]  Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
              Layer Security over Stream Control Transmission Protocol",
              RFC 3436, December 2002.


Authors' Addresses

   Michael Tuexen
   Muenster Univ. of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   Germany

   Email: tuexen@fh-muenster.de


   Robin Seggelmann
   Muenster Univ. of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   Germany

   Email: seggelmann@fh-muenster.de










Tuexen, et al.           Expires April 26, 2010                 [Page 9]

Internet-Draft                DTLS for SCTP                 October 2009


   Eric Rescorla
   RTFM, Inc.
   2064 Edgewood Drive
   Palo Alto, CA 94303
   USA

   Email: ekr@networkresonance.com












































Tuexen, et al.           Expires April 26, 2010                [Page 10]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/