Network Working Group                                          M. Tuexen
Internet-Draft                                             R. Seggelmann
Intended status: Standards Track      Muenster Univ. of Applied Sciences
Expires: January 8, 2009                                     E. Rescorla
                                                              RTFM, Inc.
                                                            July 7, 2008


   Datagram Transport Layer Security for Stream Control Transmission
                                Protocol
                draft-tuexen-tsvwg-dtls-for-sctp-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of 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 January 8, 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 all features
   provided by SCTP and its extensions, especially support of

   o  multiple streams to avoid head of line blocking.




Tuexen, et al.           Expires January 8, 2009                [Page 1]


Internet-Draft                DTLS for SCTP                    July 2008


   o  multi-homing to provide network level fault tolerance.

   o  unordered delivery.

   o  partial reliable data transfer.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  DTLS considerations . . . . . . . . . . . . . . . . . . . . . . 4
   4.  SCTP considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8






























Tuexen, et al.           Expires January 8, 2009                [Page 2]


Internet-Draft                DTLS for SCTP                    July 2008


1.  Introduction

1.1.  Overview

   This document describes the usage of the Datagram Transport Layer
   Security (DTLS) protocol, as defined in [RFC4347], over the Stream
   Control Transmission Protocol (SCTP), as defined in [RFC4960].

   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 RFC0793 [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 all
   services provided by SCTP and its partial reliability extension.  The
   dynamic modification of the IP-addresses used by the SCTP end-points
   is also supported.

   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:

   Association:  An SCTP association.

   Connection:  A TLS connection.







Tuexen, et al.           Expires January 8, 2009                [Page 3]


Internet-Draft                DTLS for SCTP                    July 2008


   Session:  A TLS session.

   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

   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 fragmentation

   The DTLS layer MUST NOT perform message fragmentation.  The SCTP
   layer will perform this task.  Thus the supported maximum length of
   SCTP user messages MUST be at least 2^14 + 2048 + 5 = 18437 bytes.
   Every DTLS message MUST be handled as one user message for SCTP.

3.2.  Message sizes

   DTLS imposes a limit in the user message size.  This limit applies
   also to DTLS/SCTP.

3.3.  Replay detection

   Replay detection of DTLS MUST NOT be used.

3.4.  Path MTU Discovery

   Path MTU discovery of DTLS MUST NOT be used.





Tuexen, et al.           Expires January 8, 2009                [Page 4]


Internet-Draft                DTLS for SCTP                    July 2008


3.5.  Retransmission of Messages

   DTLS procedures for retransmissions MUST NOT be used.


4.  SCTP considerations

4.1.  Stream usage

   All DTLS control messages MUST be transported on stream 0 with
   unlimited reliability and with the ordered delivery feature.

   User data messages MAY be transported over stream 0 but users SHOULD
   use other streams for better performance.

4.2.  Chunk handling

   The DATA, SACK 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 and SACK chunks to hide this dropping.

4.3.  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 the master secret and provided as a new end-point pair shared
   secret by using the algorithm described in
   [I-D.rescorla-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.  The Finished message MUST NOT be sent
   before all messages except the ones from this handshake have been
   acknowledged and can not be revoked anymore by the peer.

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







Tuexen, et al.           Expires January 8, 2009                [Page 5]


Internet-Draft                DTLS for SCTP                    July 2008


5.  IANA Considerations

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


6.  Security Considerations

   This section is not complete yet.


7.  Acknowledgments

   The authors wish to thank Carsten Hohendorf for his 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.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

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

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

   [I-D.rescorla-tls-extractor]
              Rescorla, E., "Keying Material Extractors for Transport
              Layer Security (TLS)", draft-rescorla-tls-extractor-01
              (work in progress), November 2007.







Tuexen, et al.           Expires January 8, 2009                [Page 6]


Internet-Draft                DTLS for SCTP                    July 2008


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


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

   Email: ekr@networkresonance.com














Tuexen, et al.           Expires January 8, 2009                [Page 7]


Internet-Draft                DTLS for SCTP                    July 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Tuexen, et al.           Expires January 8, 2009                [Page 8]