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