Network Working Group M. Tuexen Internet-Draft R. Seggelmann Intended status: Standards Track Muenster Univ. of Applied Sciences Expires:
April 25, 2009January 9, 2010 E. Rescorla RTFM, Inc. October 22, 2008July 8, 2009 Datagram Transport Layer Security for Stream Control Transmission Protocol draft-ietf-tsvwg-dtls-for-sctp-00.txtdraft-ietf-tsvwg-dtls-for-sctp-01.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 sheThis Internet-Draft is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed,submitted to IETF in accordancefull conformance with Section 6the 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 25, 2009.January 9, 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. 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 multi-homing to provide network level fault tolerance. o multiple streams to avoid head of line blocking. o multi-homing to provide network level fault tolerance. ounordered delivery. o dynamic reconfiguration of streams. o partially reliable data transfer. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 34 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3. DTLS considerationsConsiderations . . . . . . . . . . . . . . . . . . . . . . 45 4. SCTP considerationsConsiderations . . . . . . . . . . . . . . . . . . . . . . 56 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 67 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 68 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 68 8.1. Normative References . . . . . . . . . . . . . . . . . . . 68 8.2. Informative References . . . . . . . . . . . . . . . . . . 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . .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]. 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]. 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. 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 SecuritySecurity. MTU: Maximum Transmission UnitUnit. PPID: Payload Protocol Identifier. SCTP: Stream Control Transmission ProtocolProtocol. TCP: Transmission Control ProtocolProtocol. TLS: Transport Layer SecuritySecurity. 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 considerationsConsiderations 3.1. Message sizesSizes DTLS limits the DTLS user message size to the current Path MTU.MTU minus the header sizes. This limit SHOULD be increased to 2^14 Bytes for DTLS/SCTP.DTLS over SCTP. 3.2. Message fragmentationFragmentation 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 SCTP user message for SCTP.message. 3.3. Replay detectionDetection Replay detection of DTLS MUST NOT be used. 3.4. Path MTU Discovery Path MTU discovery of DTLS MUST NOT be used. 3.5. Retransmission of Messages DTLS procedures for retransmissions MUST NOT be used. 4. SCTP considerationsConsiderations 4.1. 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. 4.2. Stream usageUsage All DTLS controlmessages of the ChangeCipherSpec, Alert, or Handshake protocol MUST be transported on stream 0 with unlimited reliability and with the ordered delivery feature. User dataAll DTLS messages of the ApplicationData protocol MAY be transported over stream 0 but users SHOULD use other streams for better performance. 22.214.171.124. Chunk handlingHandling 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. 126.96.36.199. Handshake To prevent DTLS from discarding DTLS user messages while renegotiating, before sending a ClientHelloChangeCipherSpec message all outstanding SCTP user messages MUST have been acknowledged by the SCTP peer and can notMUST NOT be revoked anymore by the SCTP peer. Prior to sendingprocessing a HelloVerifyRequest,received ChangeCipherSpec all other received SCTP user messages which are buffered in the SCTP layer MUST be read from the transport layer or userand processed by DTLS. User messages arriving between ChangeCipherSpec and Finished using the new epoch have probably passed the Finished and MUST be allowed during handshake. 4.4.buffered by DTLS until the Finished is read. 4.5. Handling of endpoint-pair shared secretsEndpoint-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. TheOnce the corresponding Finished message MUST NOTfrom the peer has been received the old key SHOULD be sentremoved. 4.6. Shutdown To prevent DTLS from discarding DTLS user messages while shutting down, before sending a CloseNotify message all outstanding SCTP user messages except the ones from this handshakeMUST have been acknowledged by the SCTP peer and can notMUST NOT be revoked anymore by the SCTP peer. Once the corresponding Finished message from the peer has beenPrior to processing a received CloseNotify all other received SCTP user messages which are buffered in the old key SHOULDSCTP layer MUST be removed.read and processed by DTLS. 5. IANA Considerations IANA needs to add a value to the TLS ExtractorExporter 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. 6. Security Considerations This section isdocument does not complete yet.add any additional security considerations in addition to the ones given in [RFC4347] and [RFC4895]. 7. Acknowledgments The authors wish to thank Carsten Hohendorf, and Alfred Hoenes 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. [I-D.ietf-tls-extractor] Rescorla, E., "Keying Material ExtractorsExporters for Transport Layer Security (TLS)", draft-ietf-tls-extractor-02draft-ietf-tls-extractor-05 (work in progress), September 2008.March 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: firstname.lastname@example.org Robin Seggelmann Muenster Univ. of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: email@example.com Eric Rescorla RTFM, Inc. 2064 Edgewood Drive Palo Alto, CA 94303 USA Email: firstname.lastname@example.org 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. 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