draft-ietf-tsvwg-dtls-for-sctp-04.txt   draft-ietf-tsvwg-dtls-for-sctp-05.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: August 21, 2010 E. Rescorla Expires: September 23, 2010 E. Rescorla
RTFM, Inc. RTFM, Inc.
February 17, 2010 March 22, 2010
Datagram Transport Layer Security for Stream Control Transmission Datagram Transport Layer Security (DTLS) for Stream Control Transmission
Protocol Protocol (SCTP)
draft-ietf-tsvwg-dtls-for-sctp-04.txt draft-ietf-tsvwg-dtls-for-sctp-05.txt
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).
Security features provided by DTLS over SCTP include authentication, Security features provided by DTLS over SCTP include authentication,
message integrity and privacy of user messages. Applications using message integrity and privacy of user messages. Applications using
DTLS over SCTP can use almost all transport features provided by SCTP DTLS over SCTP can use almost all transport features provided by SCTP
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 21, 2010. This Internet-Draft will expire on September 23, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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TLS: Transport Layer Security. TLS: Transport Layer Security.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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. Future Versions of DTLS
This document is based on [RFC4347]. If a new RFC updates or
obsoletes [RFC4347], this documents also applies to the newer
document defining DTLS unless this document also gets updated or
revised.
3.2. 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. Replay Detection 3.3. Replay Detection
Replay detection of DTLS MUST NOT be used. Replay detection of DTLS MUST NOT be used.
3.3. Path MTU Discovery 3.4. Path MTU Discovery
Path MTU discovery of DTLS MUST NOT be used. Path MTU discovery of DTLS MUST NOT be used.
3.4. Retransmission of Messages 3.5. Retransmission of Messages
DTLS procedures for retransmissions MUST NOT be used. DTLS procedures for retransmissions MUST NOT be used.
3.5. Future Versions of DTLS
This document is based on [RFC4347]. If a new RFC updates or
obsoletes [RFC4347], this documents also applies to the newer
document defining DTLS unless this document also gets updated or
revised.
4. SCTP Considerations 4. SCTP Considerations
4.1. Mapping of DTLS Records 4.1. Mapping of DTLS Records
The supported maximum length of SCTP user messages MUST be at least 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 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 the DTLSCiphertext.fragment and 13 is the size of the DTLS record
header). In particular, the SCTP implementation MUST support header). In particular, the SCTP implementation MUST support
fragmentation of user messages. fragmentation of user messages.
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4.2. DTLS connection handling 4.2. DTLS connection handling
Each DTLS connection MUST be established and terminated within the Each DTLS connection MUST be established and terminated within the
same SCTP association. A DTLS connection MUST NOT span multiple SCTP same SCTP association. A DTLS connection MUST NOT span multiple SCTP
associations. associations.
4.3. Payload Protocol Identifier Usage 4.3. 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 that 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.
4.4. Stream Usage 4.4. 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
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If PR-SCTP as defined in [RFC3758] is used, FORWARD-TSN chunks MUST 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 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 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 and use forged FORWARD-TSN, SACK, and/or SHUTDOWN chunks to hide this
dropping. dropping.
4.6. Handshake 4.6. Handshake
A DTLS implementation discards DTLS messages from older epochs after A DTLS implementation discards DTLS messages from older epochs after
some time as described in section 4.1 of [RFC4347]. This is not some time, as described in section 4.1 of [RFC4347]. This is not
acceptable when the DTLS user performs a reliable data transfer. To acceptable when the DTLS user performs a reliable data transfer. To
avoid discarding messages, the following procedures are required. avoid discarding messages, the following procedures are required.
Before sending a ChangeCipherSpec message all outstanding SCTP user Before sending a ChangeCipherSpec 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 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 that 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.
4.7. Handling of Endpoint-pair Shared Secrets 4.7. 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
and MUST be used when establishing a DTLS connection. Whenever the and MUST be used when establishing a DTLS connection. Whenever the
master key changes, a 64 byte shared secret is derived from every 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 master secret and provided as a new end-point pair shared secret by
using the exporter described in [I-D.ietf-tls-extractor]. The using the exporter described in [RFC5705]. The exporter MUST use the
exporter MUST use the label given in Section 5 and an empty context. label given in Section 5 and no context. The new Shared Key
The new Shared Key Identifier MUST be the old Shared Key Identifier Identifier MUST be the old Shared Key Identifier incremented by 1.
incremented by 1. If the old one is 65535, the new one MUST be 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 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 SCTP-AUTH key SHOULD be removed. received, the old SCTP-AUTH key SHOULD be removed.
4.8. Shutdown 4.8. Shutdown
To prevent DTLS from discarding DTLS user messages while it is To prevent DTLS from discarding DTLS user messages while it is
shutting down, a CloseNotify message MUST only be sent after all shutting down, a CloseNotify message MUST only be sent after all
outstanding SCTP user messages have been acknowledged by the SCTP outstanding SCTP user messages have been acknowledged by the SCTP
peer and MUST NOT still be revoked by the SCTP peer. peer and MUST NOT still be revoked 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 that 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 [RFC5705]. The label suggested is
EXTRACTOR_DTLS_OVER_SCTP. The reference should refer to this "EXPORTER_DTLS_OVER_SCTP". The reference should refer to this
document. document.
6. Security Considerations 6. Security Considerations
The security considerations given in [RFC4347], [RFC4895], and The security considerations given in [RFC4347], [RFC4895], and
[RFC4960] also apply to this document. [RFC4960] also apply to this document.
It is possible to authenticate DTLS endpoints based on IP-addresses It is possible to authenticate DTLS endpoints based on IP-addresses
in certificates. SCTP associations can use multiple addresses per in certificates. SCTP associations can use multiple addresses per
SCTP endpoint. Therefore it is possible that DTLS records will be SCTP endpoint. Therefore it is possible that DTLS records will be
sent from a different IP-address than that originally authenticated. sent from a different IP-address than that originally authenticated.
This is not a problem provided that no security decisions are made 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: 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, all decisions should be based on the peer's authenticated identity,
not on its transport layer identity. not on its transport layer identity.
For each message the SCTP user also provides a stream identifier, a For each message, the SCTP user also provides a stream identifier, a
flag to indicate whether the message is sent ordered or unordered and flag to indicate whether the message is sent ordered or unordered and
a payload protocol identifier. Although DTLS can be used to provide a payload protocol identifier. Although DTLS can be used to provide
privacy for the actual user message, none of these three are privacy for the actual user message, none of these three are
protected by DTLS. They are sent as clear text, because they are protected by DTLS. They are sent as clear text, because they are
part of the SCTP DATA chunk header. part of the SCTP DATA chunk header.
7. Acknowledgments 7. Acknowledgments
The authors wish to thank Carsten Hohendorf, Alfred Hoenes, Daniel The authors wish to thank Carsten Hohendorf, Alfred Hoenes, Daniel
Mentz, Ian Goldberg, Anna Brunstrom, Stefan Lindskog, and Gorry Mentz, Ian Goldberg, Anna Brunstrom, Stefan Lindskog, and Gorry
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[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.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006. Security", RFC 4347, April 2006.
[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. [RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Kozuka, "Stream Control Transmission Protocol (SCTP) Layer Security (TLS)", RFC 5705, March 2010.
Dynamic Address Reconfiguration", RFC 5061,
September 2007.
[I-D.ietf-tls-extractor]
Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", draft-ietf-tls-extractor-07 (work
in progress), September 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.
[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 Authors' Addresses
Michael Tuexen Michael Tuexen
Muenster Univ. of Applied Sciences Muenster Univ. of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstr. 39
48565 Steinfurt 48565 Steinfurt
Germany Germany
Email: tuexen@fh-muenster.de Email: tuexen@fh-muenster.de
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