draft-ietf-tsvwg-sctp-auth-05.txt   draft-ietf-tsvwg-sctp-auth-06.txt 
Network Working Group M. Tuexen Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Applied Sciences Internet-Draft Muenster Univ. of Applied Sciences
Intended status: Standards Track R. Stewart Intended status: Standards Track R. Stewart
Expires: April 26, 2007 P. Lei Expires: May 28, 2007 P. Lei
Cisco Systems, Inc. Cisco Systems, Inc.
E. Rescorla E. Rescorla
RTFM, Inc. RTFM, Inc.
October 23, 2006 November 24, 2006
Authenticated Chunks for Stream Control Transmission Protocol (SCTP) Authenticated Chunks for Stream Control Transmission Protocol (SCTP)
draft-ietf-tsvwg-sctp-auth-05.txt draft-ietf-tsvwg-sctp-auth-06.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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skipping to change at page 1, line 38 skipping to change at page 1, line 38
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This Internet-Draft will expire on April 26, 2007. This Internet-Draft will expire on May 28, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document describes a new chunk type, several parameters and This document describes a new chunk type, several parameters and
procedures for SCTP. This new chunk type can be used to authenticate procedures for SCTP. This new chunk type can be used to authenticate
SCTP chunks by using shared keys between the sender and receiver. SCTP chunks by using shared keys between the sender and receiver.
The new parameters are used to establish the shared keys. The new parameters are used to establish the shared keys.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New Parameter Types . . . . . . . . . . . . . . . . . . . . . 3 3 New Parameter Types . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Random Parameter (RANDOM) . . . . . . . . . . . . . . . . 4 3.1 Random Parameter (RANDOM) . . . . . . . . . . . . . . . . . 4
3.2. Chunk List Parameter (CHUNKS) . . . . . . . . . . . . . . 4 3.2 Chunk List Parameter (CHUNKS) . . . . . . . . . . . . . . . 4
3.3. Requested HMAC Algorithm Parameter (HMAC-ALGO) . . . . . . 5 3.3 Requested HMAC Algorithm Parameter (HMAC-ALGO) . . . . . . 5
4. New Error Cause . . . . . . . . . . . . . . . . . . . . . . . 7 4 New Error Cause . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Unsupported HMAC Identifier error cause . . . . . . . . . 7 4.1 Unsupported HMAC Identifier error cause . . . . . . . . . . 7
5. New Chunk Type . . . . . . . . . . . . . . . . . . . . . . . . 7 5 New Chunk Type . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Authentication Chunk (AUTH) . . . . . . . . . . . . . . . 8 5.1 Authentication Chunk (AUTH) . . . . . . . . . . . . . . . . 8
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Establishment of an association shared key . . . . . . . . 9 6.1 Establishment of an association shared key . . . . . . . . 9
6.2. Sending authenticated chunks . . . . . . . . . . . . . . . 10 6.2 Sending authenticated chunks . . . . . . . . . . . . . . . 10
6.3. Receiving authenticated chunks . . . . . . . . . . . . . . 11 6.3 Receiving authenticated chunks . . . . . . . . . . . . . . 11
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13
8.1. A New Chunk Type . . . . . . . . . . . . . . . . . . . . . 13 8.1 A New Chunk Type . . . . . . . . . . . . . . . . . . . . . 13
8.2. Three New Parameter Types . . . . . . . . . . . . . . . . 14 8.2 Three New Parameter Types . . . . . . . . . . . . . . . . . 14
8.3. A New Error Cause . . . . . . . . . . . . . . . . . . . . 14 8.3 A New Error Cause . . . . . . . . . . . . . . . . . . . . . 14
8.4. A New Table For HMAC Identifiers . . . . . . . . . . . . . 14 8.4 A New Table For HMAC Identifiers . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9 Security Considerations . . . . . . . . . . . . . . . . . . . . 15
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 10 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 16
11. Normative References . . . . . . . . . . . . . . . . . . . . . 16 11 Normative References . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . . . 18
1. Introduction 1 Introduction
SCTP uses 32 bit verification tags to protect itself against blind SCTP uses 32 bit verification tags to protect itself against blind
attackers. These values are not changed during the lifetime of an attackers. These values are not changed during the lifetime of an
SCTP association. SCTP association.
Looking at new SCTP extensions there is the need to have a method of 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 proving that an SCTP chunk(s) was really sent by the original peer
that started the association and not by a malicious attacker. that started the association and not by a malicious attacker.
Using TLS as defined in RFC3436 [5] does not help here because it Using TLS as defined in RFC3436 [6] does not help here because it
only secures SCTP user data. only secures SCTP user data.
Therefore an SCTP extension is presented which provides a mechanism Therefore an SCTP extension is presented which provides a mechanism
for deriving shared keys for each association. These association for deriving shared keys for each association. These association
shared keys are derived from endpoint pair shared keys, which are shared keys are derived from endpoint pair shared keys, which are
configured and might be empty, and data which is exchanged during the configured and might be empty, and data which is exchanged during the
SCTP association setup. SCTP association setup.
The extension presented in this document allows an SCTP sender to The extension presented in this document allows an SCTP sender to
sign chunks using shared keys between the sender and receiver. The sign chunks using shared keys between the sender and receiver. The
receiver can then verify that the chunks are sent from the sender and receiver can then verify that the chunks are sent from the sender and
not from a malicious attacker as long as the attacker does not know not from a malicious attacker as long as the attacker does not know
an association shared key. an association shared key.
2. Conventions 2 Conventions
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL", when they appear in this document, are to be interpreted "OPTIONAL", when they appear in this document, are to be interpreted
as described in RFC2119 [3]. as described in RFC2119 [3].
3. New Parameter Types 3 New Parameter Types
This section defines the new parameter types that will be used to This section defines the new parameter types that will be used to
negotiate the authentication during association setup. Table 1 negotiate the authentication during association setup. Table 1
illustrates the new parameter types. illustrates the new parameter types.
+----------------+------------------------------------------------+ +----------------+------------------------------------------------+
| Parameter Type | Parameter Name | | Parameter Type | Parameter Name |
+----------------+------------------------------------------------+ +----------------+------------------------------------------------+
| 0x8002 | Random Parameter (RANDOM) | | 0x8002 | Random Parameter (RANDOM) |
| 0x8003 | Chunk List Parameter (CHUNKS) | | 0x8003 | Chunk List Parameter (CHUNKS) |
| 0x8004 | Requested HMAC Algorithm Parameter (HMAC-ALGO) | | 0x8004 | Requested HMAC Algorithm Parameter (HMAC-ALGO) |
+----------------+------------------------------------------------+ +----------------+------------------------------------------------+
Table 1 Table 1
It should be noted that the parameter format requires the receiver to It should be noted that the parameter format requires the receiver to
ignore the parameter and continue processing if it is not understood. ignore the parameter and continue processing if it is not understood.
This is accomplished as described in RFC2960 [4] section 3.2.1. by This is accomplished as described in RFC2960 [5] section 3.2.1. by
the use of the upper bits of the parameter type. the use of the upper bits of the parameter type.
3.1. Random Parameter (RANDOM) 3.1 Random Parameter (RANDOM)
This parameter is used to carry an arbitrary length random number. This parameter is used to carry an arbitrary length random number.
0 1 2 3 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 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 | | Parameter Type = 0x8002 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
\ Random Number / \ Random Number /
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Parameter Length: 2 bytes (unsigned integer) Parameter Length: 2 bytes (unsigned integer)
This value is the length of the Random Number in bytes plus 4. This value is the length of the Random Number in bytes plus 4.
Random Number: n bytes (unsigned integer) Random Number: n bytes (unsigned integer)
This value represents an arbitrary Random Number in network byte This value represents an arbitrary Random Number in network byte
order. order.
The RANDOM parameter MUST be included once in the INIT or INIT-ACK The RANDOM parameter MUST be included once in the INIT or INIT-ACK
chunk if the sender wants to send or receive authenticated chunks. chunk if the sender wants to send or receive authenticated chunks.
3.2. Chunk List Parameter (CHUNKS) 3.2 Chunk List Parameter (CHUNKS)
This parameter is used to specify which chunk types are required to This parameter is used to specify which chunk types are required to
be sent authenticated by the peer. be sent authenticated by the peer.
0 1 2 3 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 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 | | Parameter Type = 0x8003 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk Type 1 | Chunk Type 2 | Chunk Type 3 | Chunk Type 4 | | Chunk Type 1 | Chunk Type 2 | Chunk Type 3 | Chunk Type 4 |
skipping to change at page 5, line 40 skipping to change at page 5, line 40
The CHUNKS parameter MUST be included once in the INIT or INIT-ACK The CHUNKS parameter MUST be included once in the INIT or INIT-ACK
chunk if the sender wants to receive authenticated chunks. Its chunk if the sender wants to receive authenticated chunks. Its
maximum length is 260 bytes. maximum length is 260 bytes.
The chunk types for INIT, INIT-ACK, SHUTDOWN-COMPLETE and AUTH chunks The chunk types for INIT, INIT-ACK, SHUTDOWN-COMPLETE and AUTH chunks
MUST NOT be listed in the CHUNKS parameter. However, if a CHUNKS MUST NOT be listed in the CHUNKS parameter. However, if a CHUNKS
parameter is received then the types for INIT, INIT-ACK, SHUTDOWN- parameter is received then the types for INIT, INIT-ACK, SHUTDOWN-
COMPLETE and AUTH chunks MUST be ignored. COMPLETE and AUTH chunks MUST be ignored.
3.3. Requested HMAC Algorithm Parameter (HMAC-ALGO) 3.3 Requested HMAC Algorithm Parameter (HMAC-ALGO)
This parameter is used to list the HMAC identifiers the peer MUST This parameter is used to list the HMAC identifiers the peer MUST
use. use.
0 1 2 3 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 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 | | Parameter Type = 0x8004 | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier 1 | HMAC Identifier 2 | | HMAC Identifier 1 | HMAC Identifier 2 |
skipping to change at page 7, line 5 skipping to change at page 7, line 5
| 0 | Reserved | | 0 | Reserved |
| 1 | SHA-1 defined in [6] | | 1 | SHA-1 defined in [6] |
| 3 | SHA-256 defined in [6] | | 3 | SHA-256 defined in [6] |
+-----------------+--------------------------+ +-----------------+--------------------------+
Table 2 Table 2
Every endpoint supporting SCTP chunk authentication MUST support the Every endpoint supporting SCTP chunk authentication MUST support the
HMAC based on the SHA-1 algorithm. HMAC based on the SHA-1 algorithm.
4. New Error Cause 4 New Error Cause
This section defines a new error cause that will be sent if an AUTH This section defines a new error cause that will be sent if an AUTH
chunk is received with an unsupported HMAC identifier. Table 3 chunk is received with an unsupported HMAC identifier. Table 3
illustrates the new error cause. illustrates the new error cause.
+------------+-----------------------------+ +------------+-----------------------------+
| Cause Code | Error Cause Name | | Cause Code | Error Cause Name |
+------------+-----------------------------+ +------------+-----------------------------+
| 0x0105 | Unsupported HMAC Identifier | | 0x0105 | Unsupported HMAC Identifier |
+------------+-----------------------------+ +------------+-----------------------------+
Table 3 Table 3
4.1. Unsupported HMAC Identifier error cause 4.1 Unsupported HMAC Identifier error cause
This error cause is used to indicate that an AUTH chunk was received This error cause is used to indicate that an AUTH chunk was received
with an unsupported HMAC Identifier. with an unsupported HMAC Identifier.
0 1 2 3 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 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 = 6 | | Cause Code = 0x0105 | Cause Length = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Identifier | Padding | | HMAC Identifier | Padding |
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Cause Code: 2 bytes (unsigned integer) Cause Code: 2 bytes (unsigned integer)
This value MUST be set to 0x0105. This value MUST be set to 0x0105.
Cause Length: 2 bytes (unsigned integer) Cause Length: 2 bytes (unsigned integer)
This value MUST be set to 6. This value MUST be set to 6.
HMAC Identifier: 2 bytes (unsigned integer) HMAC Identifier: 2 bytes (unsigned integer)
This value is the HMAC Identifier which is not supported. This value is the HMAC Identifier which is not supported.
5. New Chunk Type 5 New Chunk Type
This section defines the new chunk type that will be used to This section defines the new chunk type that will be used to
authenticate chunks. Table 4 illustrates the new chunk type. authenticate chunks. Table 4 illustrates the new chunk type.
+------------+-----------------------------+ +------------+-----------------------------+
| Chunk Type | Chunk Name | | Chunk Type | Chunk Name |
+------------+-----------------------------+ +------------+-----------------------------+
| 0x0F | Authentication Chunk (AUTH) | | 0x0F | Authentication Chunk (AUTH) |
+------------+-----------------------------+ +------------+-----------------------------+
Table 4 Table 4
It should be noted that the AUTH-chunk format requires the receiver 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 to ignore the chunk if it is not understood and silently discard all
chunks that follow. This is accomplished as described in RFC2960 [4] chunks that follow. This is accomplished as described in RFC2960 [5]
section 3.2. by the use of the upper bits of the chunk type. section 3.2. by the use of the upper bits of the chunk type.
5.1. Authentication Chunk (AUTH) 5.1 Authentication Chunk (AUTH)
This chunk is used to hold the result of the HMAC calculation. This chunk is used to hold the result of the HMAC calculation.
0 1 2 3 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 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 = 0x0F | Flags=0 | Length | | Type = 0x0F | Flags=0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Key Identifier | HMAC Identifier | | Shared Key Identifier | HMAC Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 9, line 15 skipping to change at page 9, line 15
HMAC: n bytes (unsigned integer) HMAC: n bytes (unsigned integer)
This hold the result of the HMAC calculation. This hold the result of the HMAC calculation.
The control chunk AUTH MUST NOT appear more than once in an SCTP The control chunk AUTH MUST NOT appear more than once in an SCTP
packet. All control and data chunks which are placed after the AUTH packet. All control and data chunks which are placed after the AUTH
chunk in the packet are sent in an authenticated way. Those chunks chunk in the packet are sent in an authenticated way. Those chunks
placed in a packet before the AUTH chunk are not authenticated. placed in a packet before the AUTH chunk are not authenticated.
Please note that DATA chunks can not appear before control chunks in Please note that DATA chunks can not appear before control chunks in
an SCTP packet. an SCTP packet.
6. Procedures 6 Procedures
6.1. Establishment of an association shared key 6.1 Establishment of an association shared key
An SCTP endpoint willing to receive or send authenticated chunks MUST An SCTP endpoint willing to receive or send authenticated chunks MUST
send one RANDOM parameter in its INIT or INIT-ACK chunk. The RANDOM send one RANDOM parameter in its INIT or INIT-ACK chunk. The RANDOM
parameter MUST contain a 32 byte random number. If the random number parameter MUST contain a 32 byte random number. If the random number
is not 32 byte long the association MUST be aborted. The ABORT chunk is not 32 byte long the association MUST be aborted. The ABORT chunk
SHOULD contain the error cause 'Protocol Violation'. In case of INIT SHOULD contain the error cause 'Protocol Violation'. In case of INIT
collision, the rules governing the handling of this random number collision, the rules governing the handling of this random number
follow the same pattern as those for the Verification Tag, as follow the same pattern as those for the Verification Tag, as
explained in section 5.2.4 of RFC2960 [4]. Therefore each endpoint explained in section 5.2.4 of RFC2960 [5]. Therefore each endpoint
knows its own random number and the peer's random number after the knows its own random number and the peer's random number after the
association has been established. association has been established.
An SCTP endpoint has a list of chunks it only accepts if they are 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 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 does and INIT-ACK and MAY be omitted if it is empty. Since this list does
not change during the lifetime of there is no problem in case of INIT not change during the lifetime of there is no problem in case of INIT
collision. collision.
Each SCTP endpoint MUST include in the INIT and INIT-ACK a HMAC-ALGO Each SCTP endpoint MUST include in the INIT and INIT-ACK a HMAC-ALGO
skipping to change at page 10, line 19 skipping to change at page 10, line 19
the smaller key number and concatenating it to the endpoint pair the smaller key number and concatenating it to the endpoint pair
shared key, and then concatenating the larger of the key numbers to shared key, and then concatenating the larger of the key numbers to
that. If both key numbers are equal, then the concatenation order is that. If both key numbers are equal, then the concatenation order is
the endpoint shared key, followed by the key number with the shorter the endpoint shared key, followed by the key number with the shorter
length, followed by the key number with the longer length. If the length, followed by the key number with the longer length. If the
key number lengths are the same, then they may be concatenated to the key number lengths are the same, then they may be concatenated to the
endpoint pair key in any order. The concatenation is performed on endpoint pair key in any order. The concatenation is performed on
byte vectors representing all numbers in network byte order. The byte vectors representing all numbers in network byte order. The
result is the association shared key. result is the association shared key.
6.2. Sending authenticated chunks 6.2 Sending authenticated chunks
Endpoints MUST send all requested chunks authenticated where this has Endpoints MUST send all requested chunks authenticated where this has
been requested by the peer. The other chunks MAY be sent been requested by the peer. The other chunks MAY be sent
authenticated or not. If endpoint pair shared keys are used, one of authenticated or not. If endpoint pair shared keys are used, one of
them MUST be selected for authentication. them MUST be selected for authentication.
To send chunks in an authenticated way, the sender MUST include these To send chunks in an authenticated way, the sender MUST include these
chunks after an AUTH chunk. This means that a sender MUST bundle chunks after an AUTH chunk. This means that a sender MUST bundle
chunks in order to authenticate them. chunks in order to authenticate them.
skipping to change at page 11, line 12 skipping to change at page 11, line 12
Figure 6 Figure 6
Please note that all fields are in network byte order and that the Please note that all fields are in network byte order and that the
field which will contain the complete HMAC is filled with zeroes. 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 The length of the field shown as 0 is the length of the HMAC
described by the HMAC Identifier. The padding of all chunks being described by the HMAC Identifier. The padding of all chunks being
authenticated MUST be included in the HMAC computation. authenticated MUST be included in the HMAC computation.
The sender fills the HMAC into the HMAC field and sends the packet. The sender fills the HMAC into the HMAC field and sends the packet.
6.3. Receiving authenticated chunks 6.3 Receiving authenticated chunks
The receiver has a list of chunk types which it expects to be 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 received only after an AUTH-chunk. This list has been sent to the
peer during the association setup. It MUST silently discard these peer during the association setup. It MUST silently discard these
chunks if they are not placed after an AUTH chunk in the packet. chunks if they are not placed after an AUTH chunk in the packet.
The receiver MUST use the HMAC algorithm indicated in the HMAC The receiver MUST use the HMAC algorithm indicated in the HMAC
Identifier field. If this algorithm was not specified by the Identifier field. If this algorithm was not specified by the
receiver in the HMAC-ALGO parameter in the INIT or INIT-ACK chunk receiver in the HMAC-ALGO parameter in the INIT or INIT-ACK chunk
during association setup, the AUTH chunk and all chunks after it MUST during association setup, the AUTH chunk and all chunks after it MUST
skipping to change at page 12, line 41 skipping to change at page 12, line 41
shared key. But it should also be noted that if an endpoint accepts shared key. But it should also be noted that if an endpoint accepts
ABORT chunks only in an authenticated way, it may take longer to ABORT chunks only in an authenticated way, it may take longer to
detect that the peer is no longer available. If an endpoint accepts detect that the peer is no longer available. If an endpoint accepts
COOKIE-ECHO chunks only in an authenticated way, the restart COOKIE-ECHO chunks only in an authenticated way, the restart
procedure does not work. procedure does not work.
Furthermore it is important that the cookie contained in an INIT-ACK Furthermore it is important that the cookie contained in an INIT-ACK
chunk and in a COOKIE-ECHO chunk MUST NOT contain the end-point pair chunk and in a COOKIE-ECHO chunk MUST NOT contain the end-point pair
shared key. shared key.
7. Examples 7 Examples
This section gives examples of message exchanges for association This section gives examples of message exchanges for association
setup. setup.
The simplest way of using the extension described in this document is The simplest way of using the extension described in this document is
given by the following message exchange. given by the following message exchange.
---------- INIT[RANDOM; CHUNKS; HMAC-ALGO] ----------> ---------- INIT[RANDOM; CHUNKS; HMAC-ALGO] ---------->
<------- INIT-ACK[RANDOM; CHUNKS; HMAC-ALGO] --------- <------- INIT-ACK[RANDOM; CHUNKS; HMAC-ALGO] ---------
-------------------- COOKIE-ECHO --------------------> -------------------- COOKIE-ECHO -------------------->
skipping to change at page 13, line 34 skipping to change at page 13, line 34
the processing of the COOKIE-ECHO chunk (COMMUNICATION-UP the processing of the COOKIE-ECHO chunk (COMMUNICATION-UP
notification followed by the presentation of the endpoint pair shared notification followed by the presentation of the endpoint pair shared
key by the upper layer to the SCTP stack) and the processing of the key by the upper layer to the SCTP stack) and the processing of the
AUTH and DATA chunk at the server side. If this intervention is not AUTH and DATA chunk at the server side. If this intervention is not
possible due to limitations of the API (for example the socket API) possible due to limitations of the API (for example the socket API)
the server might discard the AUTH and DATA chunk making a the server might discard the AUTH and DATA chunk making a
retransmission of the DATA chunk necessary. If the same endpoint retransmission of the DATA chunk necessary. If the same endpoint
pair shared key is used for multiple endpoints and does not depend on pair shared key is used for multiple endpoints and does not depend on
the client this intervention might not be necessary. the client this intervention might not be necessary.
8. IANA Considerations 8 IANA Considerations
[NOTE to RFC-Editor: [NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this "RFCXXXX" is to be replaced by the RFC number you assign this
document. document.
] ]
This document (RFCXXX) is the reference for all registrations This document (RFCXXX) is the reference for all registrations
described in this section. All registrations need to be listed in described in this section. All registrations need to be listed in
the document available at sctp-parameters [7]. The suggested changes the document available at sctp-parameters [8]. The suggested changes
are described below. are described below.
8.1. A New Chunk Type 8.1 A New Chunk Type
A chunk type for the AUTH chunk has to be assigned by IANA. It is A chunk type for the AUTH chunk has to be assigned by IANA. It is
suggested to use the value given in Table 4. This requires an suggested to use the value given in Table 4. This requires an
additional line in the "CHUNK TYPES" table of sctp-parameters [7]: additional line in the "CHUNK TYPES" table of sctp-parameters [8]:
CHUNK TYPES CHUNK TYPES
ID Value Chunk Type Reference ID Value Chunk Type Reference
----- ---------- --------- ----- ---------- ---------
15 Authentication Chunk (AUTH) [RFCXXXX] 15 Authentication Chunk (AUTH) [RFCXXXX]
8.2. Three New Parameter Types 8.2 Three New Parameter Types
Parameter types have to be assigned for the RANDOM, CHUNKS, and HMAC- Parameter types have to be assigned for the RANDOM, CHUNKS, and HMAC-
ALGO parameter by IANA. It is suggested to use the values given in ALGO parameter by IANA. It is suggested to use the values given in
Table 1. This requires two modifications of the "CHUNK PARAMETER Table 1. This requires two modifications of the "CHUNK PARAMETER
TPYES" tables in sctp-parameters [7]: The first change is the TPYES" tables in sctp-parameters [8]: The first change is the
addition of three new lines to the "INIT Chunk Parameter Types" addition of three new lines to the "INIT Chunk Parameter Types"
table: table:
Chunk Parameter Type Value Chunk Parameter Type Value
-------------------- ----- -------------------- -----
Random 32770 (0x8002) Random 32770 (0x8002)
Chunk List 32771 (0x8003) Chunk List 32771 (0x8003)
Requested HMAC Algorithm Parameter 32772 (0x8004) Requested HMAC Algorithm Parameter 32772 (0x8004)
The second required change is the addition of the same three lines to The second required change is the addition of the same three lines to
the to the "INIT ACK Chunk Parameter Types" table. the to the "INIT ACK Chunk Parameter Types" table.
8.3. A New Error Cause 8.3 A New Error Cause
An error cause for the Unsupported HMAC Identifier error cause has to An error cause for the Unsupported HMAC Identifier error cause has to
be assigned. It is suggested to use the value given in Table 3. be assigned. It is suggested to use the value given in Table 3.
This requires an additional line of the "CAUSE CODES" table in sctp- This requires an additional line of the "CAUSE CODES" table in sctp-
parameters [7]: parameters [8]:
VALUE CAUSE CODE REFERENCE VALUE CAUSE CODE REFERENCE
----- ---------------- --------- ----- ---------------- ---------
261 (0x0105) Unsupported HMAC Identifier RFCXXXX 261 (0x0105) Unsupported HMAC Identifier RFCXXXX
8.4. A New Table For HMAC Identifiers 8.4 A New Table For HMAC Identifiers
HMAC Identifiers have to be maintained by IANA. Three initial values HMAC Identifiers have to be maintained by IANA. Three initial values
should be assigned by IANA as described in Table 2. This requires a should be assigned by IANA as described in Table 2. This requires a
new table "HMAC IDENTIFIERS" in sctp-parameters [7]: new table "HMAC IDENTIFIERS" in sctp-parameters [8]:
HMAC Identifier Message Digest Algorithm REFERENCE HMAC Identifier Message Digest Algorithm REFERENCE
--------------- ------------------------ --------- --------------- ------------------------ ---------
0 Reserved RFCXXXX 0 Reserved RFCXXXX
1 SHA-1 RFCXXXX 1 SHA-1 RFCXXXX
3 SHA-256 RFCXXXX 3 SHA-256 RFCXXXX
For registering at IANA a new HMAC Identifier in this table a request For registering at IANA a new HMAC Identifier in this table a request
has to be made to assign such a number. This number must be unique has to be made to assign such a number. This number must be unique
and a message digest algorithm usable with the HMAC defined in and a message digest algorithm usable with the HMAC defined in
RFC2104 [2] MUST be specified. RFC2104 [2] MUST be specified. The "Specification Required" policy
of RFC2434 [4] MUST be applied.
9. Security Considerations 9 Security Considerations
Without using endpoint shared keys this extension only protects Without using endpoint shared keys this extension only protects
against modification or injection of authenticated chunks by against modification or injection of authenticated chunks by
attackers who did not capture the initial handshake setting up the attackers who did not capture the initial handshake setting up the
SCTP association. SCTP association.
If an endpoint pair shared key is used even a true man in the middle If an endpoint pair shared key is used even a true man in the middle
cannot inject chunks which are required to be authenticated even if cannot inject chunks which are required to be authenticated even if
he intercepts the initial message exchange. The endpoint also knows he intercepts the initial message exchange. The endpoint also knows
that it is accepting authenticated chunks from a peer who knows the that it is accepting authenticated chunks from a peer who knows the
skipping to change at page 16, line 5 skipping to change at page 16, line 5
setup the association and modifies or removes this CHUNKS parameter setup the association and modifies or removes this CHUNKS parameter
this endpoint will not accept chunks which are authenticated or needs this endpoint will not accept chunks which are authenticated or needs
to be authenticated and are not. This might result in the failure of to be authenticated and are not. This might result in the failure of
the association. the association.
When an endpoint pair uses non-NULL endpoint pair shared keys and one When an endpoint pair uses non-NULL endpoint pair shared keys and one
of the endpoints still accepts a NULL key an attacker who captured of the endpoints still accepts a NULL key an attacker who captured
the initial handshake can still inject or modify authenticated chunks the initial handshake can still inject or modify authenticated chunks
by using the NULL key. by using the NULL key.
10. Acknowledgments 10 Acknowledgments
The authors wish to thank Sascha Grau, Ivan Arias Rodriguez, Irene The authors wish to thank Sascha Grau, Ivan Arias Rodriguez, Irene
Ruengeler, and Magnus Westerlund for their invaluable comments. Ruengeler, and Magnus Westerlund for their invaluable comments.
11. Normative References 11. Normative References
[1] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [1] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992. April 1992.
[2] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing [2] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997. for Message Authentication", RFC 2104, February 1997.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[4] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[5] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
"Stream Control Transmission Protocol", RFC 2960, October 2000. "Stream Control Transmission Protocol", RFC 2960, October 2000.
[5] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer [6] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer
Security over Stream Control Transmission Protocol", RFC 3436, Security over Stream Control Transmission Protocol", RFC 3436,
December 2002. December 2002.
[6] National Institute of Standards and Technology, "Secure Hash [7] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-2, August 2002, Standard", FIPS PUB 180-2, August 2002,
<http://csrc.nist.gov/publications/fips/fips180-2/ <http://csrc.nist.gov/publications/fips/fips180-2/
fips180-2.pdf>. fips180-2.pdf>.
[7] <http://www.iana.org/assignments/sctp-parameters> [8] <http://www.iana.org/assignments/sctp-parameters>
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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