draft-ietf-tsvwg-dtls-for-sctp-01.txt   draft-ietf-tsvwg-dtls-for-sctp-02.txt 
Network Working Group M. Tuexen Network Working Group M. Tuexen
Internet-Draft R. Seggelmann Internet-Draft R. Seggelmann
Intended status: Standards Track Muenster Univ. of Applied Sciences Intended status: Standards Track Muenster Univ. of Applied Sciences
Expires: January 9, 2010 E. Rescorla Expires: April 26, 2010 E. Rescorla
RTFM, Inc. RTFM, Inc.
July 8, 2009 October 23, 2009
Datagram Transport Layer Security for Stream Control Transmission Datagram Transport Layer Security for Stream Control Transmission
Protocol Protocol
draft-ietf-tsvwg-dtls-for-sctp-01.txt draft-ietf-tsvwg-dtls-for-sctp-02.txt
Status of this Memo Status of this Memo
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Abstract Abstract
This document describes the usage of the Datagram Transport Layer This document describes the usage of the Datagram Transport Layer
Security (DTLS) protocol over the Stream Control Transmission Security (DTLS) protocol over the Stream Control Transmission
Protocol (SCTP). Protocol (SCTP).
The user of DTLS over SCTP can take advantage of all features The user of DTLS over SCTP can take advantage of most of the features
provided by SCTP and its extensions, especially support of provided by SCTP and its extensions, especially support of
o multi-homing to provide network level fault tolerance. 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 multiple streams to avoid head of line blocking.
o unordered delivery. o unordered delivery.
o dynamic reconfiguration of streams. o dynamic reconfiguration of streams.
o partially reliable data transfer. 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.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . . 5 3. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . . 5
4. SCTP Considerations . . . . . . . . . . . . . . . . . . . . . . 6 4. SCTP Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
1.1. Overview 1.1. Overview
This document describes the usage of the Datagram Transport Layer This document describes the usage of the Datagram Transport Layer
Security (DTLS) protocol, as defined in [RFC4347], over the Stream Security (DTLS) protocol, as defined in [I-D.ietf-tls-rfc4347-bis],
Control Transmission Protocol (SCTP), as defined in [RFC4960]. over the Stream Control Transmission Protocol (SCTP), as defined in
[RFC4960].
TLS is designed to run on top of a byte-stream oriented transport TLS, from which DTLS was derived, is designed to run on top of a
protocol providing a reliable, in-sequence delivery. Thus, TLS is byte-stream oriented transport protocol providing a reliable, in-
currently mainly being used on top of the Transmission Control sequence delivery. Thus, TLS is currently mainly being used on top
Protocol (TCP), as defined in [RFC0793]. of the Transmission Control Protocol (TCP), as defined in [RFC0793].
TLS over SCTP as described in [RFC3436] has some serious limitations: 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 the unordered delivery of SCTP user messages.
o It does not support partial reliability as defined in [RFC3758]. 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 o It only supports the usage of the same number of streams in both
directions. directions.
o It uses a TLS connection for every bidirectional stream, which o It uses a TLS connection for every bidirectional stream, which
requires a substantial amount of resources and message exchanges requires a substantial amount of resources and message exchanges
if a large number of streams is used. if a large number of streams is used.
DTLS over SCTP as described in this document overcomes these DTLS over SCTP as described in this document overcomes these
limitations of TLS over SCTP. The user of DTLS over SCTP can use all limitations of TLS over SCTP. The user of DTLS over SCTP can use
services provided by SCTP and its partial reliability extension. The almost all services provided by SCTP and its partial reliability
dynamic modification of the IP-addresses used by the SCTP end-points extension. However, DTLS limits the user message size to 2^14 bytes.
is also supported. 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 The method described in this document requires that the SCTP
implementation supports the optional feature of fragmentation of SCTP implementation supports the optional feature of fragmentation of SCTP
user messages and the SCTP authentication extension defined in user messages and the SCTP authentication extension defined in
[RFC4895]. [RFC4895].
1.2. Terminology 1.2. Terminology
This document uses the following terms: This document uses the following terms:
Association: An SCTP association. Association: An SCTP association.
Connection: A TLS connection.
Session: A TLS session.
Stream: A unidirectional stream of an SCTP association. It is Stream: A unidirectional stream of an SCTP association. It is
uniquely identified by a stream identifier. uniquely identified by a stream identifier.
1.3. Abbreviations 1.3. Abbreviations
DTLS: Datagram Transport Layer Security. DTLS: Datagram Transport Layer Security.
MTU: Maximum Transmission Unit. MTU: Maximum Transmission Unit.
PPID: Payload Protocol Identifier. PPID: Payload Protocol Identifier.
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document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. DTLS Considerations 3. DTLS Considerations
3.1. Message Sizes 3.1. Message Sizes
DTLS limits the DTLS user message size to the current Path MTU minus 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 the header sizes. This limit SHOULD be increased to 2^14 Bytes for
DTLS over SCTP. DTLS over SCTP.
3.2. Message Fragmentation 3.2. Replay Detection
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.
3.3. Replay Detection
Replay detection of DTLS MUST NOT be used. Replay detection of DTLS MUST NOT be used.
3.4. Path MTU Discovery 3.3. Path MTU Discovery
Path MTU discovery of DTLS MUST NOT be used. Path MTU discovery of DTLS MUST NOT be used.
3.5. Retransmission of Messages 3.4. Retransmission of Messages
DTLS procedures for retransmissions MUST NOT be used. DTLS procedures for retransmissions MUST NOT be used.
4. SCTP Considerations 4. SCTP Considerations
4.1. Payload Protocol Identifier Usage 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 Application protocols running over DTLS over SCTP SHOULD register and
use a separate payload protocol identifier (PPID) and SHOULD NOT use a separate payload protocol identifier (PPID) and SHOULD NOT
reuse the PPID which they registered for running directly over SCTP. reuse the PPID which they registered for running directly over SCTP.
This means in particular that there is no specific PPID for DTLS. This means in particular that there is no specific PPID for DTLS.
4.2. Stream Usage 4.3. Stream Usage
All DTLS messages of the ChangeCipherSpec, Alert, or Handshake All DTLS messages of the ChangeCipherSpec, Alert, or Handshake
protocol MUST be transported on stream 0 with unlimited reliability protocol MUST be transported on stream 0 with unlimited reliability
and with the ordered delivery feature. and with the ordered delivery feature.
All DTLS messages of the ApplicationData protocol MAY be transported All DTLS messages of the ApplicationData protocol MAY be transported
over stream 0 but users SHOULD use other streams for better over stream 0 but users SHOULD use other streams to avoid possible
performance. performance problems due to head of line blocking.
4.3. Chunk Handling 4.4. Chunk Handling
The DATA, SACK and FORWARD-TSN chunks of SCTP MUST be sent in an The DATA, SACK, SHUTDOWN, and FORWARD-TSN chunks of SCTP MUST be sent
authenticated way as described in [RFC4895]. Other chunks MAY be in an authenticated way as described in [RFC4895]. Other chunks MAY
sent in an authenticated way. be sent in an authenticated way.
This makes sure that an attacker can not modify the stream a message 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. 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 It is also not possible for an attacker to drop messages and use
forged FORWARD-TSN and SACK chunks to hide this dropping. forged FORWARD-TSN, SACK, and/or SHUTDOWN chunks to hide this
dropping.
4.4. Handshake 4.5. Handshake
To prevent DTLS from discarding DTLS user messages while A DTLS implementation discards DTLS messages from older epochs after
renegotiating, before sending a ChangeCipherSpec message all some time as described in section 4.1 of [I-D.ietf-tls-rfc4347-bis].
outstanding SCTP user messages MUST have been acknowledged by the This is not acceptable when the DTLS user performs a reliable data
SCTP peer and MUST NOT be revoked anymore by the SCTP peer. transfer. To avoid the discarding of 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 anymore by the SCTP peer.
Prior to processing a received ChangeCipherSpec all other received Prior to processing a received ChangeCipherSpec all other received
SCTP user messages which are buffered in the SCTP layer MUST be read SCTP user messages which are buffered in the SCTP layer MUST be read
and processed by DTLS. and processed by DTLS.
User messages arriving between ChangeCipherSpec and Finished using User messages arriving between ChangeCipherSpec and Finished using
the new epoch have probably passed the Finished and MUST be buffered the new epoch have probably passed the Finished and MUST be buffered
by DTLS until the Finished is read. by DTLS until the Finished is read.
4.5. Handling of Endpoint-pair Shared Secrets 4.6. Handling of Endpoint-pair Shared Secrets
The endpoint-pair shared secret for Shared Key Identifier 0 is empty. The endpoint-pair shared secret for Shared Key Identifier 0 is empty.
Whenever the master key changes, a 64 byte shared secret is derived 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 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]. 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 Shared Key Identifier MUST be incremented by 1. If it is 65535,
the next value MUST be 1. the next value MUST be 1.
Before sending the Finished message the active SCTP-AUTH key MUST be Before sending the Finished message the active SCTP-AUTH key MUST be
switched to the new one. switched to the new one.
Once the corresponding Finished message from the peer has been Once the corresponding Finished message from the peer has been
received the old key SHOULD be removed. received the old SCTP-AUTH key SHOULD be removed.
4.6. Shutdown 4.7. Shutdown
To prevent DTLS from discarding DTLS user messages while shutting To prevent DTLS from discarding DTLS user messages while shutting
down, before sending a CloseNotify message all outstanding SCTP user down, before sending a CloseNotify message all outstanding SCTP user
messages MUST have been acknowledged by the SCTP peer and MUST NOT be messages MUST have been acknowledged by the SCTP peer and MUST NOT be
revoked anymore by the SCTP peer. revoked anymore by the SCTP peer.
Prior to processing a received CloseNotify all other received SCTP Prior to processing a received CloseNotify all other received SCTP
user messages which are buffered in the SCTP layer MUST be read and user messages which are buffered in the SCTP layer MUST be read and
processed by DTLS. processed by DTLS.
5. IANA Considerations 5. IANA Considerations
IANA needs to add a value to the TLS Exporter Label registry as IANA needs to add a value to the TLS Exporter Label registry as
described in [I-D.ietf-tls-extractor]. The label suggested is described in [I-D.ietf-tls-extractor]. The label suggested is
EXTRACTOR_DTLS_OVER_SCTP. The reference should refer to this EXTRACTOR_DTLS_OVER_SCTP. The reference should refer to this
document. document.
6. Security Considerations 6. Security Considerations
This document does not add any additional security considerations in The security considerations given in [I-D.ietf-tls-rfc4347-bis],
addition to the ones given in [RFC4347] and [RFC4895]. [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 7. Acknowledgments
The authors wish to thank Carsten Hohendorf, and Alfred Hoenes for The authors wish to thank Carsten Hohendorf, Alfred Hoenes, Daniel
their invaluable comments. Mentz, Ian Goldberg, Anna Brunstrom, and Stefan Lindskog for their
invaluable comments.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. [RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP) Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004. 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, [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission "Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, August 2007. Protocol (SCTP)", RFC 4895, August 2007.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007. RFC 4960, September 2007.
[I-D.ietf-tls-extractor] [I-D.ietf-tls-extractor]
Rescorla, E., "Keying Material Exporters for Transport Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", draft-ietf-tls-extractor-05 (work Layer Security (TLS)", draft-ietf-tls-extractor-07 (work
in progress), March 2009. 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 8.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol", Layer Security over Stream Control Transmission Protocol",
RFC 3436, December 2002. RFC 3436, December 2002.
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