GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6083

Internet Engineering Task Force (IETF) M. Tuexen Request for Comments: 6083 R. Seggelmann Category: Standards Track Muenster Univ. of Applied Sciences ISSN: 2070-1721 E. Rescorla

                                                            RTFM, Inc.
                                                          January 2011
              Datagram Transport Layer Security (DTLS)
          for Stream Control Transmission Protocol (SCTP)

Abstract

 This document describes the usage of the Datagram Transport Layer
 Security (DTLS) protocol over the Stream Control Transmission
 Protocol (SCTP).
 DTLS over SCTP provides communications privacy for applications that
 use SCTP as their transport protocol and allows client/server
 applications to communicate in a way that is designed to prevent
 eavesdropping and detect tampering or message forgery.
 Applications using DTLS over SCTP can use almost all transport
 features provided by SCTP and its extensions.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6083.

Tuexen, et al. Standards Track [Page 1] RFC 6083 DTLS for SCTP January 2011

Copyright Notice

 Copyright (c) 2011 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
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
 3.  DTLS Considerations . . . . . . . . . . . . . . . . . . . . . . 4
 4.  SCTP Considerations . . . . . . . . . . . . . . . . . . . . . . 5
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
 6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
 7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8

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].
 DTLS over SCTP provides communications privacy for applications that
 use SCTP as their transport protocol and allows client/server
 applications to communicate in a way that is designed to prevent
 eavesdropping and detect tampering or message forgery.
 Applications using DTLS over SCTP can use almost all transport
 features provided by SCTP and its extensions.
 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].

Tuexen, et al. Standards Track [Page 2] RFC 6083 DTLS for SCTP January 2011

 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.  In particular, DTLS/SCTP supports:
 o  preservation of message boundaries.
 o  a large number of unidirectional and bidirectional streams.
 o  ordered and unordered delivery of SCTP user messages.
 o  the partial reliability extension as defined in [RFC3758].
 o  the dynamic address reconfiguration extension as defined in
    [RFC5061].
 However, the following limitations still apply:
 o  The maximum user message size is 2^14 bytes, which is the DTLS
    limit.
 o  The DTLS user cannot 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 as defined in [RFC4960] and the SCTP authentication
 extension defined in [RFC4895].

1.2. Terminology

 This document uses the following terms:
 Association:  An SCTP association.
 Stream:  A unidirectional stream of an SCTP association.  It is
    uniquely identified by a stream identifier.

Tuexen, et al. Standards Track [Page 3] RFC 6083 DTLS for SCTP January 2011

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. Version of DTLS

 This document is based on [RFC4347], and it is expected that DTLS/
 SCTP as described in this document will work with future versions of
 DTLS.

3.2. Message Sizes

 DTLS limits the DTLS user message size to the current Path MTU minus
 the header sizes.  For the purposes of running over SCTP, the DTLS
 path MTU MUST be considered to be 2^14.

3.3. Replay Detection

 The replay detection of DTLS may result in the DTLS layer dropping
 messages.  Since DTLS/SCTP provides a reliable service if requested
 by the application, replay detection cannot be used.  Therefore,
 replay detection of DTLS MUST NOT be used.

3.4. Path MTU Discovery

 SCTP provides Path MTU discovery and fragmentation/reassembly for
 user messages.  According to Section 3.2, DTLS can send maximum sized
 messages.  Therefore, Path MTU discovery of DTLS MUST NOT be used.

Tuexen, et al. Standards Track [Page 4] RFC 6083 DTLS for SCTP January 2011

3.5. Retransmission of Messages

 SCTP provides a reliable and in-sequence transport service for DTLS
 messages that require it.  See Section 4.4.  Therefore, DTLS
 procedures for retransmissions MUST NOT be used.

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. DTLS Connection Handling

 Each DTLS connection MUST be established and terminated within the
 same SCTP association.  A DTLS connection MUST NOT span multiple SCTP
 associations.

4.3. Payload Protocol Identifier Usage

 Application protocols using DTLS over SCTP SHOULD register and use a
 separate payload protocol identifier (PPID) and SHOULD NOT reuse the
 PPID that they registered for running directly over SCTP.
 Using the same PPID does not harm as long as the application can
 determine whether or not DTLS is used.  However, for protocol
 analyzers, for example, it is much easier if a separate PPID is used.
 This means, in particular, that there is no specific PPID for DTLS.

4.4. 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.
 DTLS messages of the ApplicationData protocol SHOULD use multiple
 streams other than stream 0; they MAY use stream 0 for everything if
 they do not care about minimizing head of line blocking.

Tuexen, et al. Standards Track [Page 5] RFC 6083 DTLS for SCTP January 2011

4.5. Chunk Handling

 DATA 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 cannot modify the stream in which a
 message is sent or affect the ordered/unordered delivery of the
 message.
 If PR-SCTP as defined in [RFC3758] is used, FORWARD-TSN chunks MUST
 also be sent in an authenticated way as described in [RFC4895].  This
 makes sure that it is not possible for an attacker to drop messages
 and use forged FORWARD-TSN, SACK, and/or SHUTDOWN chunks to hide this
 dropping.

4.6. Renegotiation

 DTLS supports renegotiation, and therefore this feature is also
 available by DTLS/SCTP.  It is up to the upper layer to use/allow it
 or not.  Application writers should be aware that allowing
 renegotiations may result in changes of security parameters.

4.7. Handshake

 A DTLS implementation discards DTLS messages from older epochs after
 some time, as described in Section 4.1 of [RFC4347].  This is not
 acceptable when the DTLS user performs a reliable data transfer.  To
 avoid discarding messages, the following 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 by the SCTP peer.
 Prior to processing a received ChangeCipherSpec, all other received
 SCTP user messages that are buffered in the SCTP layer MUST be read
 and processed by DTLS.
 User messages that arrive between ChangeCipherSpec and Finished
 messages and use the new epoch have probably passed the Finished
 message and MUST be buffered by DTLS until the Finished message is
 read.

4.8. Handling of Endpoint-Pair Shared Secrets

 The endpoint-pair shared secret for Shared Key Identifier 0 is empty
 and MUST be used when establishing a DTLS connection.  Whenever the
 master key changes, a 64-byte shared secret is derived from every
 master secret and provided as a new endpoint-pair shared secret by
 using the exporter described in [RFC5705].  The exporter MUST use the

Tuexen, et al. Standards Track [Page 6] RFC 6083 DTLS for SCTP January 2011

 label given in Section 5 and no context.  The new Shared Key
 Identifier MUST be the old Shared Key Identifier incremented by 1.
 If the old one is 65535, the new one 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.

4.9. Shutdown

 To prevent DTLS from discarding DTLS user messages while it is
 shutting down, a CloseNotify message MUST only be sent after all
 outstanding SCTP user messages have been acknowledged by the SCTP
 peer and MUST NOT still be revoked by the SCTP peer.
 Prior to processing a received CloseNotify, all other received SCTP
 user messages that are buffered in the SCTP layer MUST be read and
 processed by DTLS.

5. IANA Considerations

 IANA added a value to the TLS Exporter Label registry as described in
 [RFC5705].  The label is "EXPORTER_DTLS_OVER_SCTP".

6. Security Considerations

 The security considerations given in [RFC4347], [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.
 For each message, the SCTP user also provides a stream identifier, a
 flag to indicate 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.

Tuexen, et al. Standards Track [Page 7] RFC 6083 DTLS for SCTP January 2011

 DTLS supports cipher suites that contain a NULL cipher algorithm.
 Negotiating a NULL cipher algorithm will not provide communications
 privacy for applications and will not provide privacy for user
 messages.

7. Acknowledgments

 The authors wish to thank Anna Brunstrom, Lars Eggert, Gorry
 Fairhurst, Ian Goldberg, Alfred Hoenes, Carsten Hohendorf, Stefan
 Lindskog, Daniel Mentz, and Sean Turner 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.
 [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.
 [RFC5705]  Rescorla, E., "Keying Material Exporters for Transport
            Layer Security (TLS)", RFC 5705, March 2010.

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.

Tuexen, et al. Standards Track [Page 8] RFC 6083 DTLS for SCTP January 2011

 [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
            Kozuka, "Stream Control Transmission Protocol (SCTP)
            Dynamic Address Reconfiguration", RFC 5061,
            September 2007.

Authors' Addresses

 Michael Tuexen
 Muenster University of Applied Sciences
 Stegerwaldstr. 39
 48565 Steinfurt
 Germany
 EMail: tuexen@fh-muenster.de
 Robin Seggelmann
 Muenster University 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. Standards Track [Page 9]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6083.txt · Last modified: 2011/01/20 17:46 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki