One document matched: draft-ietf-tsvwg-sctp-auth-00.txt
Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Applied Sciences
Expires: December 14, 2005 R. Stewart
P. Lei
Cisco Systems, Inc.
E. Rescorla
RTFM, Inc.
June 12, 2005
Authenticated Chunks for Stream Control Transmission Protocol (SCTP)
draft-ietf-tsvwg-sctp-auth-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes a new chunk type, several parameters and
procedures for SCTP. This new chunk type can be used to authenticate
SCTP chunks by using a shared key between the sender and receiver.
The new parameters are used to establish the shared key.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New Parameter Types . . . . . . . . . . . . . . . . . . . . 3
3.1 Random Parameter (RANDOM) . . . . . . . . . . . . . . . . 4
3.2 Chunk List Parameter (CHUNKS) . . . . . . . . . . . . . . 4
3.3 Requested HMAC Algorithm Parameter (HMAC-ALGO) . . . . . . 5
4. New Error Cause . . . . . . . . . . . . . . . . . . . . . . 6
4.1 Unsupported HMAC Identifier error cause . . . . . . . . . 7
5. New Chunk Type . . . . . . . . . . . . . . . . . . . . . . . 7
5.1 Authentication Chunk (AUTH) . . . . . . . . . . . . . . . 8
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1 Establishment of an association shared key . . . . . . . . 8
6.2 Sending authenticated chunks . . . . . . . . . . . . . . . 9
6.3 Receiving authenticated chunks . . . . . . . . . . . . . . 10
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . 11
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1 Normative References . . . . . . . . . . . . . . . . . . 12
11.2 Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . 14
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1. Introduction
SCTP uses 32 bit verification tags to protect itself against blind
attackers. These values are not changed during the lifetime of an
SCTP association.
Looking at new SCTP extensions there is the need to have a method of
proving that an SCTP chunk(s) was really sent by the original peer
that started the association and not by a malicious attacker.
Using TLS as defined in RFC3436 [6] does not help here because it
only secures SCTP user data.
Therefore an SCTP extension is presented in this document which
allows an SCTP sender to sign chunks using a shared key between the
sender and receiver. The receiver can then verify, that the chunks
are sent from the sender and not from a malicious attacker.
This extension also provides a mechanism for deriving a shared key
for each association. This association shared key is derived from a
endpoint pair shared key, which is preconfigured and might be empty.
2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
RFC2119 [4].
3. New Parameter Types
This section defines the new parameter types that will be used to
negotiate the authentication during association setup. Figure 1
illustrates the new parameter types.
Parameter Type Parameter Name
--------------------------------------------------------------
0x8002 Random Parameter (RANDOM)
0x8003 Chunk List Parameter (CHUNKS)
0x8004 Requested HMAC Algorithm Parameter (HMAC-ALGO)
Figure 1
It should be noted that the parameter format requires the receiver to
ignore the parameter and continue processing if it is not understood.
This is accomplished as described in RFC2960 [5] section 3.2.1. by
the use of the upper bit of the parameter type.
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3.1 Random Parameter (RANDOM)
This parameter is used to carry an arbitrary length random number.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 0x8002 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
\ Random Number /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
Parameter Type: 2 bytes (unsigned integer) This value MUST be set to
0x8002.
Parameter Length: 2 bytes (unsigned integer) This value is the length
of the Random Number plus 4.
Random Number: n bytes (unsigned integer) This value represents an
arbitrary Random Number in network byte order.
The RANDOM parameter MUST be included once in the INIT or INIT-ACK
chunk if the sender wants to send or receive authenticated chunks.
3.2 Chunk List Parameter (CHUNKS)
This parameter is used to specify which chunk types are required to
be sent authenticated by the peer.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 0x8003 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk Type 1 | Chunk Type 2 | Chunk Type 4 | Chunk Type 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk Type n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
Parameter Type: 2 bytes (unsigned integer) This value MUST be set to
0x8003.
Parameter Length: 2 bytes (unsigned integer) This value is the number
of listed Chunk Types plus 4.
Chunk Type n: 1 byte (unsigned integer) Each Chunk Type listed is
required to be authenticated when sent by the peer.
The CHUNKS parameter MUST be included once in the INIT or INIT-ACK
chunk if the sender wants to receive authenticated chunks. Its
maximum length is 260 bytes.
The chunk types for INIT, INIT-ACK, COOKIE-ECHO, COOKIE-ACK,
SHUTDOWN-COMPLETE and AUTH chunks MUST not be listed in the CHUNKS
parameter. However, if a CHUNKS parameter is received then the types
for INIT, INIT-ACK, COOKIE-ECHO, COOKIE-ACK, SHUTDOWN-COMPLETE and
AUTH chunks MUST be ignored.
3.3 Requested HMAC Algorithm Parameter (HMAC-ALGO)
This parameter is used to list the HMAC identifiers the peer has to
use.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 0x8004 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4
Parameter Type: 2 bytes (unsigned integer) This value MUST be set to
0x8004.
Parameter Length: 2 bytes (unsigned integer) This value is the length
of the number of HMAC identifiers times 4 plus 4.
HMAC Identifier n: 4 bytes (unsigned integer) The values is a a
requested HMAC Identifier.
The HMAC-ALGO parameter MUST be included once in the INIT or INIT-ACK
chunk if the sender wants to send or receive authenticated chunks.
The following Figure 5 shows the currently defined values for HMAC
identifiers.
HMAC Identifier Message Digest Algorithm
---------------------------------------------------------------
0 Reserved
1 SHA-1 defined in [10]
2 MD-5 defined in [1]
Figure 5
Every endpoint supporting SCTP chunk authentication MUST support the
HMAC based on the SHA-1 algorithm.
4. New Error Cause
This section defines a new error cause that will be sent if an AUTH
chunk is received with an unsupported HMAC identifier. Figure 6
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illustrates the new error cause.
Cause Code Error Cause Name
--------------------------------------------------------------
0x0105 Unsupported HMAC Identifier
Figure 6
4.1 Unsupported HMAC Identifier error cause
This error cause is used to indicate that an AUTH chunk was received
with an unsupported HMAC Identifier.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code = 0x0105 | Cause Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7
Cause Code: 2 bytes (unsigned integer) This value MUST be set to
0x0105.
Cause Length: 2 bytes (unsigned integer) This value MUST be set to 8.
HMAC Identifier: 4 bytes (unsigned integer) This value is the HMAC
Identifier which is not supported.
5. New Chunk Type
This section defines the new chunk type that will be used to
authenticate chunks. Figure 8 illustrates the new chunk type.
Chunk Type Chunk Name
--------------------------------------------------------------
0x83 Authentication Chunk (AUTH)
Figure 8
It should be noted that the AUTH-chunk format requires the receiver
to ignore the chunk if it is not understood and silently discard all
chunks that follow. This is accomplished as described in RFC2960 [5]
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section 3.2. by the use of the upper bit of the chunk type.
5.1 Authentication Chunk (AUTH)
This chunk is used to hold the result of the HMAC calculation.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x83 | Flags=0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
\ HMAC /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9
Type: 1 byte (unsigned integer) This value MUST be set to 0x83 for
all AUTH-chunks.
Flags: 1 byte (unsigned integer) Set to zero on transmit and ignored
on receipt.
Length: 2 bytes (unsigned integer) This value holds the length of the
HMAC plus 8.
HMAC Identifier: 4 bytes (unsigned integer) This value describes
which message digest is being used. Figure 5 shows the currently
defined values.
HMAC: n bytes (unsigned integer) This hold the result of the HMAC
calculation.
The control chunk AUTH can appear at most once in an SCTP packet.
All control and data chunks which are placed after the AUTH chunk in
the packet are sent in an authenticated way. Those chunks placed in
a packet before the AUTH chunk are not authenticated.
6. Procedures
6.1 Establishment of an association shared key
An SCTP endpoint willing to receive or send authenticated chunks has
to send one RANDOM parameter in its INIT or INIT-ACK chunk. The
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RANDOM parameter SHOULD contain a 32 byte random number. This random
number is handled like the verification tag in case of INIT
collisions. Therefore each endpoint knows its own random number and
the peers random number after the association has been established.
An SCTP endpoint has a list of chunks it only accepts if they are
received in an authenticated way. This list is included in the INIT
and INIT-ACK and MAY be omitted if it is empty. Since this list is
for an endpoint there is no problem in case of INIT collision.
Each SCTP endpoint MUST include in the INIT and INIT-ACK a HMAC-ALGO
parameter containing a list of HMAC Identifiers it requests the peer
to use. The receiver of a HMAC-ALGO parameter SHOULD use the first
listed algorithm it supports. The HMAC algorithm based on SHA-1 MUST
be supported and included in the HMAC-ALGO parameter. An SCTP
endpoint MUST not change the parameters listed in the HMAC-ALGO
parameter during the lifetime of the endpoint.
Both enpoints of an association have an endpoint pair shared key
which is a byte vector and preconfigured or established by another
mechanism. If it is not preconfigured or established by another
mechanism it is set to the empty byte vector.
From this endpoint pair shared key the association shared key is
computed by concatenating the endpoint pair shared key with the
random numbers exchanged in the INIT and INIT-ACK. This is performed
by selecting the smaller random number and concatenating it to the
endpoint pair shared key. Then concatenating the larger of the
random numbers to that. If both random numbers are equal they may be
concatenated to the endpoint pair key in any order. The
concatenation is performed on byte vectors representing all numbers
in network byte order. The result is the association shared key.
6.2 Sending authenticated chunks
Chunks can only be authenticated when the SCTP association is in the
ESTABLISHED state. Both endpoints MUST send all those chunks
authenticated where this has been requested by the peer. The other
chunks MAY be sent authenticated.
To send chunks in an authenticated way, the sender has to include
these chunks after an AUTH chunk. This means that a sender MUST
bundle chunks in order to authenticate them.
The sender MUST calculate the MAC using the hash function H as
described by the MAC Identifier and the shared association key K. The
'data' used for the computation of the AUTH-chunk is given by
Figure 10 and all chunks that are placed after the AUTH chunk in the
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SCTP packet. RFC2104 [3] can be used as a guideline for generating
the MAC.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x83 | Flags=0 | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
\ 0 /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10
Please note that all fields are in network byte order and that the
field which will contain the complete HMAC is filled with zeroes.
The length of the field shown as 0 is the length of the HMAC
described by the HMAC Identifier.
The sender fills the HMAC into the HMAC field and sends the packet.
6.3 Receiving authenticated chunks
The receiver has a list of chunk types which it expects to be
received only after an AUTH-chunk. This list has been sent to the
peer during the association setup. It MUST silently discard these
chunks if they are not placed after an AUTH chunk in the packet.
The receiver MUST use the HMAC algorithm indicated in the HMAC
Identifier field. If this algorithm is not known the AUTH chunk and
all chunks after it MUST be discarded and an ERROR chunk SHOULD be
sent with the error cause defined in Section 4.1.
The receiver now performs the same calculation as described for the
sender based on Figure 10. If the result of the calculation is the
same as given in the HMAC field, all chunks following the AUTH chunk
are processed. If the field does not match the result of the
calculation all these chunks MUST be silently discarded.
It should be noted that if the receiver wants to tear down an
association in an authenticated way only, the handling of malformed
packets should be in tune with this.
7. Examples
This section gives examples of message exchanges for association
setup.
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The simplest way of using the extension described in this document is
given by the following message exchange.
---------- INIT[RANDOM; CHUNKS; HMAC-ALGO] ---------->
<------- INIT-ACK[RANDOM; CHUNKS; HMAC-ALGO] ---------
-------------------- COOKIE-ECHO -------------------->
<-------------------- COOKIE-ACK ---------------------
Please note that the CHUNKS parameter is optional in the INIT and
INIT-ACK.
If the server wants to receive DATA chunks in an authenticated way,
the following message exchange is possible:
---------- INIT[RANDOM; CHUNKS; HMAC-ALGO] ---------->
<------- INIT-ACK[RANDOM; CHUNKS; HMAC-ALGO] ---------
--------------- COOKIE-ECHO; AUTH; DATA ------------->
<----------------- COOKIE-ACK; SACK ------------------
Please note that if the endpoint pair shared key depends on the
client and the server and that it is only known by the upper layer
this message exchange requires an upper layer intervention between
the processing of the COOKIE-ECHO chunk (COMMUNICATION-UP
notification followed by the presentation of the endpoint pair shared
key by the upper layer to the SCTP stack) and the processing of the
AUTH and DATA chunk. If this intervention is not possible due to
limitations of the API the server might discard the AUTH and DATA
chunk making a retransmission of the DATA chunk necessary. If the
same endpoint pair shared key is used for multiple endpoints and does
not depend on the client this intervention might not be necessary.
8. IANA Considerations
A chunk type for the AUTH chunk has to be assigned by IANA. It is
suggested to use the value given above.
Parameter types have to be assigned for the RANDOM, CHUNKS, and HMAC-
ALGO parameter by IANA. It is suggested to use the values given
above.
HMAC Identifiers have to be maintained by IANA. Three initial values
should be assigned by IANA as described above.
9. Security Considerations
This section is still incomplete.
If no endpoint pair shared key is used an attacker which captures the
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association setup message exchange can later insert arbitrary packets
in an authenticated way. However, if the attacker did not capture
this initial message exchange he can not successfully inject chunks
which are required to be authenticated.
If an enpoint pair shared key is used even a true man in the middle
can not inject chunks which are required to be authenticated even if
he intercepts the initial message exchange.
Because SCTP has already a mechanism built-in that handles the
reception of duplicated chunks the presented solution makes use of
this functionality and does not provide a method to avoid replay
attacks by itself. Of course, this only works within each SCTP
association. Therefore a separate shared key is used for each SCTP
association to handle replay attacks covering multiple SCTP
associations.
10. Acknowledgments
The authors wish to thank Sascha Grau for his invaluable comments.
11. References
11.1 Normative References
[1] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[2] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
[3] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000.
[6] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer
Security over Stream Control Transmission Protocol", RFC 3436,
December 2002.
[7] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-1, April 1995,
<http://www.itl.nist.gov/fipspubs/fip180-1.htm>.
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11.2 Informative References
[8] Stewart, R., "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration",
draft-ietf-tsvwg-addip-sctp-12 (work in progress), June 2005.
Authors' Addresses
Michael Tuexen
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany
Email: tuexen@fh-muenster.de
Randall R. Stewart
Cisco Systems, Inc.
4875 Forest Drive
Suite 200
Columbia, SC 29206
USA
Email: rrs@cisco.com
Peter Lei
Cisco Systems, Inc.
8735 West Higgins Road
Suite 300
Chicago, IL 60631
USA
Phone:
Email: peterlei@cisco.com
Eric Rescorla
RTFM, Inc.
2064 Edgewood Drive
Palo Alto, CA 94303
USA
Phone: +1 650-320-8549
Email: ekr@rtfm.com
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