draft-ietf-tcpm-tcp-auth-opt-00.txt   draft-ietf-tcpm-tcp-auth-opt-01.txt 
TCPM WG J. Touch TCPM WG J. Touch
Internet Draft USC/ISI Internet Draft USC/ISI
Obsoletes: 2385 A. Mankin Obsoletes: 2385 A. Mankin
Intended status: Proposed Standard R. Bonica Intended status: Proposed Standard R. Bonica
Expires: May 2008 Juniper Networks Expires: January 2009 Juniper Networks
November 11, 2007 July 14, 2008
The TCP Authentication Option The TCP Authentication Option
draft-ietf-tcpm-tcp-auth-opt-00.txt draft-ietf-tcpm-tcp-auth-opt-01.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that By submitting this Internet-Draft, each author represents that
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aware have been or will be disclosed, and any of which he or she aware have been or will be disclosed, and any of which he or she
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BCP 79. BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
skipping to change at page 1, line 36 skipping to change at page 1, line 36
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on May 11, 2007. This Internet-Draft will expire on January 14, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract Abstract
This document specifies a TCP Authentication Option (TCP-AO) which is This document specifies a TCP Authentication Option (TCP-AO) which is
intended to replace the TCP MD5 Signature option of RFC-2385 (TCP intended to replace the TCP MD5 Signature option of RFC-2385 (TCP
MD5). TCP-AO specifies the use of stronger Message Authentication MD5). TCP-AO specifies the use of stronger Message Authentication
Codes (MACs) and provides more details on the association of security Codes (MACs) and provides more details on the association of security
associations with TCP connections. TCP-AO assumes an external, out- associations with TCP connections. TCP-AO assumes an external, out-
of-band mechanism (manual or via a separate protocol) for session key of-band mechanism (manual or via a separate protocol) for session key
establishment, parameter negotiation, and rekeying, replicating the establishment, parameter negotiation, and rekeying, replicating the
separation of key management and key use as in the IPsec suite. The separation of key management and key use as in the IPsec suite. The
result is intended to be a simple modification to support current result is intended to be a simple modification to support current
infrastructure uses of TCP MD5, such as to protect BGP and LDP, and infrastructure uses of TCP MD5, such as to protect BGP and LDP, and
to support a larger set of MACs with minimal other system and to support a larger set of MACs with minimal other system and
operational changes. TCP-AO uses a new option identifier, even though operational changes. TCP-AO uses a new option identifier, even though
it is intended to be mutually exclusive with TCP MD5 on a given TCP it is intended to be mutually exclusive with TCP MD5 on a given TCP
connection. It supports IPv6, and is fully compatible with connection. It supports IPv6, and is fully compatible with
requirements under development for an update to TCP MD5. requirements under development for an update to TCP MD5.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
1.1. Executive Summary.........................................4 1.1. Executive Summary.........................................3
1.2. Changes from Previous Versions............................5 1.2. List of TBD Items.........................................5
1.2.1. New in draft-touch-tcp-simple-auth-03................6 1.3. List of currently pending issues and to-do items..........5
1.2.2. New in draft-touch-tcp-simple-auth-02................7 1.4. Changes from Previous Versions............................6
1.2.3. New in draft-touch-tcp-simple-auth-01................7 1.4.1. New in draft-ietf-tcp-auth-opt-01....................6
1.3. Summary of RFC-2119 Requirements..........................8 1.4.2. New in draft-ietf-tcp-auth-opt-00....................6
2. The TCP Simple Authentication Option...........................8 1.4.3. New in draft-touch-tcp-simple-auth-03................7
2.1. Review of TCP MD5 Option..................................8 1.4.4. New in draft-touch-tcp-simple-auth-02................7
2.2. TCP-AO Option.............................................9 1.4.5. New in draft-touch-tcp-simple-auth-01................7
3. Security Association Management...............................12 1.5. Summary of RFC-2119 Requirements..........................8
4. TCP-AO Interaction with TCP...................................15 2. Conventions used in this document..............................8
4.1. User Interface...........................................15 3. The TCP Simple Authentication Option...........................8
4.2. TCP States and Transitions...............................16 3.1. Review of TCP MD5 Option..................................8
4.3. TCP Segments.............................................16 3.2. TCP-AO Option.............................................9
4.4. Sending TCP Segments.....................................17 4. Security Association Management...............................12
4.5. Receiving TCP Segments...................................18 5. TCP-AO Interaction with TCP...................................14
4.6. Impact on TCP Header Size................................19 5.1. User Interface...........................................14
5. Key Establishment and Duration Issues.........................19 5.2. TCP States and Transitions...............................15
5.1. Implementing the TSAD as an External Database............20 5.3. TCP Segments.............................................15
6. Interactions with TCP MD5.....................................21 5.4. Sending TCP Segments.....................................16
7. Interactions with NAT/NAPT Devices............................22 5.5. Receiving TCP Segments...................................17
8. Evaluation of Requirements Satisfaction.......................22 5.6. Impact on TCP Header Size................................18
9. Security Considerations.......................................25 6. Key Establishment and Duration Issues.........................18
10. IANA Considerations..........................................27 6.1. Implementing the TSAD as an External Database............19
11. Acknowledgments..............................................27 7. Interactions with TCP MD5.....................................20
12. References...................................................27 8. Interactions with NAT/NAPT Devices............................21
12.1. Normative References....................................27 9. Evaluation of Requirements Satisfaction.......................21
12.2. Informative References..................................28 10. Security Considerations......................................24
Author's Addresses...............................................29 11. IANA Considerations..........................................26
Intellectual Property Statement..................................30 12. Acknowledgments..............................................26
Disclaimer of Validity...........................................30 13. References...................................................26
13.1. Normative References....................................26
13.2. Informative References..................................27
1. Introduction 1. Introduction
The TCP MD5 Signature (TCP MD5) is a TCP option that authenticates The TCP MD5 Signature (TCP MD5) is a TCP option that authenticates
TCP segments, including the TCP IPv4 pseudoheader, TCP header, and TCP segments, including the TCP IPv4 pseudoheader, TCP header, and
TCP data. It was developed to protect BGP sessions from spoofed TCP TCP data. It was developed to protect BGP sessions from spoofed TCP
segments which could affect BGP data or the robustness of the TCP segments which could affect BGP data or the robustness of the TCP
connection itself [RFC2385][RFC4953]. connection itself [RFC2385][RFC4953].
There have been many recently-documented concerns about TCP MD5. Its There have been many recently-documented concerns about TCP MD5. Its
use of a simple keyed hash for authentication is problematic because use of a simple keyed hash for authentication is problematic because
there have been escalating attacks on the algorithm itself [Be05] there have been escalating attacks on the algorithm itself [Be05]
[Bu06]. TCP MD5 also lacks both key management and algorithm [Bu06]. TCP MD5 also lacks both key management and algorithm agility.
agility. This document proposes to add the latter, but suggests that This document proposes to add the latter, but suggests that TCP
TCP should not be the framework for cryptographic key management. should not be the framework for cryptographic key management. This
This document replaces the TCP MD5 option to become a more general document replaces the TCP MD5 option to become a more general TCP
TCP Authentication Option (TCP-AO), to support the use of other, Authentication Option (TCP-AO), to support the use of other, stronger
stronger hash functions and to provide a more structured hash functions and to provide a more structured recommendation on
recommendation on external key management. The result is compatible external key management. The result is compatible with IPv6, and is
with IPv6, and is fully compatible with requirements under fully compatible with requirements under development for an update to
development for an update to TCP MD5 [Be07]. TCP MD5 [Be07].
This document is not intended to replace the use of the IPsec suite This document is not intended to replace the use of the IPsec suite
(IPsec and IKE) to protect TCP connections [RFC4301][RFC4306]. In (IPsec and IKE) to protect TCP connections [RFC4301][RFC4306]. In
fact, we recommend the use of IPsec and IKE, especially where IKE's fact, we recommend the use of IPsec and IKE, especially where IKE's
level of existing support for parameter negotiation, session key level of existing support for parameter negotiation, session key
negotiation, or rekeying are desired. TCP-AO is intended for use only negotiation, or rekeying are desired. TCP-AO is intended for use only
where the IPsec suite would not be feasible, e.g., as has been where the IPsec suite would not be feasible, e.g., as has been
suggested is the case for some routing protocols, or in cases where suggested is the case for some routing protocols, or in cases where
keys need to be tightly coordinated with individual transport keys need to be tightly coordinated with individual transport
sessions [Be07]. sessions [Be07].
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once established. once established.
1.1. Executive Summary 1.1. Executive Summary
This document replaces TCP MD5 as follows [RFC2385]: This document replaces TCP MD5 as follows [RFC2385]:
o Uses a separate option Kind for TCP-AO (TBD-IANA-KIND). o Uses a separate option Kind for TCP-AO (TBD-IANA-KIND).
o Allows TCP MD5 to continue to be used for other connections. o Allows TCP MD5 to continue to be used for other connections.
o Replaces MD5's one implicit MAC algorith with two prespecified o Replaces MD5's one implicit MAC algorithm with two prespecified
MACs (TBD-WG-MACS), and allows other MACs at the implementer's MACs (TBD-WG-MACS), and allows other MACs at the implementer's
discretion. discretion.
o Allows rekeying during a TCP connection, assuming that an out-of- o Allows rekeying during a TCP connection, assuming that an out-of-
band protocol or manual mechanism coordinates the change of key band protocol or manual mechanism coordinates the change of key
and that incorrectly keyed segments are ignored. In such cases, a and that incorrectly keyed segments are ignored. In such cases, a
key ID may be used to make key selection more efficient. key ID makes key selection more efficient.
o Provides more detail in how this option interacts with TCP's o Provides more detail in how this option interacts with TCP's
states, event processing, and user interface. states, event processing, and user interface.
o Proposed option is 4 bytes shorter (14 bytes overall, rather than o Proposed option is 3 bytes shorter (15 bytes overall, rather than
18) in the default case (assuming a 96-bit MAC, TBD-WG-MACLEN). 18) in the default case (assuming a 96-bit MAC, TBD-WG-MACLEN).
This document differs from other proposals to update TCP MD5 as This document differs from other proposals to update TCP MD5 in that
follows [Bo07][We05][We07]: TCP-AO: [Bo07][We05][We07]:
o Fully compatible with requirements currently under development. o Is fully compatible with requirements currently under development.
o Does not support dynamic parameter negotiation. o Does not support dynamic parameter negotiation.
o Does not support in-band session key negotiation. o Does not support in-band session key negotiation.
o Does not support in-band session rekeying. o Does not support in-band session rekeying.
o Does not require additional timers. o Does not require additional timers.
o Always authenticates the the segment pseudoheader, header, and o Always authenticates the the segment pseudoheader, header, and
data. data.
o Provides more detail in how this option interacts with TCP's o Provides more detail in how this option interacts with TCP's
states, event processing, and user interface. states, event processing, and user interface.
o Proposed option is 2 bytes shorter (14 bytes overall, rather than o Is shorter than TCP MD5 in the default case.
16) in the default case (assuming a 96-bit MAC, TBD-WG-MACLEN)
o Does not expose the MAC algorithm in the header. o Does not expose the MAC algorithm in the header.
o Does not require a key ID; it allows for one where key overlap is o Requires a key ID.
desired to support efficient rekeying.
o Supports TCP over either IPv4 or IPv6. o Supports TCP over either IPv4 or IPv6.
This document differs from an IPsec/IKE solution as follows This document differs from an IPsec/IKE solution in that TCP-AO
[RFC4301][RFC4306]: [RFC4301][RFC4306]:
o Does not support dynamic parameter negotiation. o Does not support dynamic parameter negotiation.
o Does not require a key ID (SPI), but does allow one. o Does not require a key ID (SPI), but does allow one.
o Does not protect from replay attacks. o Does not protect from replay attacks.
o Forces a change of connection key when a connection restarts, even o Forces a change of connection key when a connection restarts, even
when reusing a TCP socket pair (IP addresses and port numbers) when reusing a TCP socket pair (IP addresses and port numbers)
skipping to change at page 5, line 46 skipping to change at page 5, line 36
TBD-IANA-KIND new TCP option Kind for TCP-AO, assigned by IANA TBD-IANA-KIND new TCP option Kind for TCP-AO, assigned by IANA
TBD-WG-MACS list of default required MAC algorithms TBD-WG-MACS list of default required MAC algorithms
TBD-WG-MACLEN default length of MAC used in the TCP-AO MAF TBD-WG-MACLEN default length of MAC used in the TCP-AO MAF
1.3. List of currently pending issues and to-do items 1.3. List of currently pending issues and to-do items
[NOTE: to be omitted upon final publication as an RFC] [NOTE: to be omitted upon final publication as an RFC]
o Should the KeyID field always be present, or is the odd/even o [IESG] Should this document deprecate TCP MD5?
solution currently described preferred?
o Should TCP options be a list (as currently specified), all-or-none o [SAAG] Which two MAC algorithms should be required as default?
(i.e., a single bit), or always included (i.e., non-configurable)? Should one be set as the primary default?
o Which two MAC algorithms should be required as default? Should one
be set as the primary default?
o Should the TSAD have a flag indicating use of the KeyID field (as o [TCPM] Should TCP-AO include a negotiation protocol with a
is currently defined), or should a KeyID=0 in the TSAD indicate backoff, i.e., to allow non-TCP-AO endpoints to connect more
that no key is being used? quickly (or is this a security problem)? Note that this would be
useful only where a rapid failure is useful, or where the TCP
might backoff and use another mode (e.g., TCP MD5 or no
authentication).
o Should TCP-AO include a negotiation protocol with a backoff, i.e., o [EDITORS TO-DO] Add a discussion of the use with manual keys, esp.
to allow non-TCP-AO endpoints to connect more quickly (or is this for connections with dynamic source ports.
a security problem)? Note that this would be useful only where a
rapid failure is useful, or where the TCP might backoff and use
another mode (e.g., TCP MD5 or no authentication).
o Should the TSAD include entries for TCP MD5, or should that o [EDITORS TO-DO] Review need for LISTEN instructions.
protocol be deprecated implicitly and thus not supported per se by
this document?
o TO-DO: Add a discussion of the use with manual keys, esp. for 1.4. Changes from Previous Versions
connections with dynamic source ports.
o TO-DO: Fix change to STATUS that makes it write-mode; current TCP [NOTE: to be omitted upon final publication as RFC]
STATUS is read-only.
o TO-DO: Review need for LISTEN instructions. 1.4.1. New in draft-ietf-tcp-auth-opt-01
1.4. Changes from Previous Versions o Require KeyID in all versions. Remove odd/even indicator of KeyID
usage.
[NOTE: to be omitted upon final publication as RFC] o Relax restrictions on key reuse: requiring an algorithm for nonce
introduction based on ISNs, and suggest key rollover every 2^31
bytes (rather than using an extended sequence number, which
introduces new state to the TCP connection).
1.4.1. New in draft-ietf-tcp-auth-opt-00 o Clarify NAT interaction; currently does not support omitting the
IP addresses or TCP ports, both of which would be required to
support NATs without any coordination. This appears to present a
problem for key management - if the key manager knows the received
addrs and ports, it should coordinate them (as indicated in Sec
8).
o Options are included or excluded all-or-none. Excluded options are
deleted, not just zeroed, to avoid the impact of reordering or
length changes of such options.
o Clarified key words to exclude lower case usage.
1.4.2. New in draft-ietf-tcp-auth-opt-00
o List of TBD values, and indication of how each is determined. o List of TBD values, and indication of how each is determined.
o Changed TCP-SA to TCP-AO (removed 'simple' throughout). o Changed TCP-SA to TCP-AO (removed 'simple' throughout).
o Removed proposed NAT mechanism; cited RFC-3947 NAT-T as o Removed proposed NAT mechanism; cited RFC-3947 NAT-T as
appropriate approach instead. appropriate approach instead.
o Made several changes coordinated in the TCP-AUTH-DT as follow: o Made several changes coordinated in the TCP-AUTH-DT as follow:
skipping to change at page 7, line 15 skipping to change at page 7, line 13
o Allow 0 as a legitimate KeyID. o Allow 0 as a legitimate KeyID.
o Allow the WG to determine the two appropriate required MAC o Allow the WG to determine the two appropriate required MAC
algorithms. algorithms.
o Add TO-DO items. o Add TO-DO items.
o Added discussion at end of Introduction as to why TCP MD5 o Added discussion at end of Introduction as to why TCP MD5
connections cannot be upgraded to TCP-AO. connections cannot be upgraded to TCP-AO.
1.4.2. New in draft-touch-tcp-simple-auth-03 1.4.3. New in draft-touch-tcp-simple-auth-03
o Added support for NAT/NAPT. o Added support for NAT/NAPT.
o Added support for IPv6. o Added support for IPv6.
o Added discussion of how this proposal satisfies requirements under o Added discussion of how this proposal satisfies requirements under
development, including those indicated in [Be07]. development, including those indicated in [Be07].
o Clarified the byte order of all data used in the MAC. o Clarified the byte order of all data used in the MAC.
o Changed the TCP option exclusion bit from a bit to a list. o Changed the TCP option exclusion bit from a bit to a list.
1.4.3. New in draft-touch-tcp-simple-auth-02 1.4.4. New in draft-touch-tcp-simple-auth-02
o Add reference to Bellovin's need-for-TCP-auth doc [Be07]. o Add reference to Bellovin's need-for-TCP-auth doc [Be07].
o Add reference to SP4 [SDNS88]. o Add reference to SP4 [SDNS88].
o Added notes that TSAD to be externally implemented; this was o Added notes that TSAD to be externally implemented; this was
compatible with the TSAD described in the previous version. compatible with the TSAD described in the previous version.
o Augmented the protocol to allow a KeyID, required to support o Augmented the protocol to allow a KeyID, required to support
efficient overlapping keys during rekeying, and potentially useful efficient overlapping keys during rekeying, and potentially useful
during connection establishment. Accommodated by redesigning the during connection establishment. Accommodated by redesigning the
TSAD. TSAD.
o Added the odd/even indicator for the KeyID. o Added the odd/even indicator for the KeyID.
o Allow for the exclusion of all TCP options in the MAC calculation. o Allow for the exclusion of all TCP options in the MAC calculation.
1.4.4. New in draft-touch-tcp-simple-auth-01 1.4.5. New in draft-touch-tcp-simple-auth-01
o Allows intra-session rekeying, assuming out-of-band coordination. o Allows intra-session rekeying, assuming out-of-band coordination.
o MUST allow TSAD entries to change, enabling rekeying within a TCP o MUST allow TSAD entries to change, enabling rekeying within a TCP
connection. connection.
o Omits discussion of the impact of connection reestablishment on o Omits discussion of the impact of connection reestablishment on
BGP, because added support for rekeying renders this point moot. BGP, because added support for rekeying renders this point moot.
o Adds further discussion on the need for rekeying. o Adds further discussion on the need for rekeying.
1.5. Summary of RFC-2119 Requirements 1.5. Summary of RFC-2119 Requirements
[NOTE: a summary will be placed here prior to last call] [NOTE: a summary will be placed here prior to last call]
2. The TCP Simple Authentication Option 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. The TCP Simple Authentication Option
The TCP Simple Authentication Option (TCP-AO) uses a new TCP option The TCP Simple Authentication Option (TCP-AO) uses a new TCP option
Kind value, (TBD-IANA-KIND). Kind value, (TBD-IANA-KIND).
2.1. Review of TCP MD5 Option 3.1. Review of TCP MD5 Option
For review, the TCP MD5 option is shown in Figure 1. For review, the TCP MD5 option is shown in Figure 1.
+---------+---------+-------------------+ +---------+---------+-------------------+
| Kind=19 |Length=18| MD5 digest... | | Kind=19 |Length=18| MD5 digest... |
+---------+---------+-------------------+ +---------+---------+-------------------+
| | | |
+---------------------------------------+ +---------------------------------------+
| | | |
+---------------------------------------+ +---------------------------------------+
skipping to change at page 9, line 5 skipping to change at page 9, line 17
1. the TCP pseudoheader (IP source and destination addresses, 1. the TCP pseudoheader (IP source and destination addresses,
protocol number, and segment length) protocol number, and segment length)
2. TCP header excluding options and checksum 2. TCP header excluding options and checksum
3. TCP data 3. TCP data
4. connection key 4. connection key
2.2. TCP-AO Option 3.2. TCP-AO Option
The new TCP-AO option is intended to be a superset of the TCP MD5 The new TCP-AO option is intended to be a superset of the TCP MD5
capability, and to be minimal in the spirit of SP4 [SDNS88]. TCP-AO capability, and to be minimal in the spirit of SP4 [SDNS88]. TCP-AO
uses a new Kind field, and similar Length field to TCP MD5, and is uses a new Kind field, and similar Length field to TCP MD5, and is
shown in Figure 2. shown in Figure 2.
+--------------------+---------+-----------------... +---------------------+---------+-------------------+
| Kind=TBD-IANA-KIND | Len=var | MAF... ... | Kind= TBD-IANA-KIND | Len=var | MAC |
+--------------------+---------+-----------------... +---------------------+---------+-------------------+
| MAC (con't) ...
+-------------------------------------...
...-----------------+---------+
... MAC (con't) | KeyID |
...-----------------+---------+
Figure 2 Proposed TCP-AO Option Figure 2 Proposed TCP-AO Option
The TCP-AO defines the following fields: The TCP-AO defines the following fields:
o Kind: An unsigned field indicating the TCP-AO Option. TCP-AO uses o Kind: An unsigned field indicating the TCP-AO Option. TCP-AO uses
a new Kind value=TBD-IANA-KIND. Because of how keys are managed a new Kind value=TBD-IANA-KIND. Because of how keys are managed
(see Section 3), an endpoint will not use TCP-AO for the same (see Section 4), an endpoint will not use TCP-AO for the same
connection where TCP MD5 is used. connection where TCP MD5 is used.
o Length: An unsigned 8-bit field indicating the length of the TCP- o Length: An unsigned 8-bit field indicating the length of the TCP-
AO option in bytes, including the Kind and Length fields. AO option in bytes, including the Kind, Length, and KeyID fields.
>> The Length MUST be greater than or equal to 2. >> The Length MUST be greater than or equal to 3.
>> The Length value MUST be consistent with the TCP header length; >> The Length value MUST be consistent with the TCP header length;
this is a consistency check and to avoid overrun/underrun abuse. this is a consistency check and to avoid overrun/underrun abuse.
Values of 2 and other small values are of dubious utility (e.g., Values of 3 and other small values are of dubious utility (e.g.,
for MAC=NONE, or for very short MACs) but not specifically for MAC=NONE, or for very short MACs) but not specifically
prohibited. See the MAF description for implications of odd/even prohibited.
lengths.
o MAF: The MAF is a Message Authentication Field. Its contents are
determined by the particulars of the security association, where
there are two possible variants. When the Length is even, the
option appears as in Figure 3. When the Length is odd, the option
appears as in Figure 4.
+--------------------+---------+-------------------+
| Kind=TBD-IANA-KIND | Len=var | MAC |
+--------------------+---------+-------------------+
| MAC (con't)... ...
+-------------------------------------...
Figure 3 TCP-AO MAF without key identifier
+---------------------+---------+-------------------+
| Kind= TBD-IANA-KIND | Len=var | MAC |
+---------------------+---------+-------------------+
| MAC (con't)... ...
+-------------------+---------+-------...
...-----------------+---------+
... MAC (con't) | KeyID |
...-----------------+---------+
Figure 4 TCP-AO MAF with key identifier
Typical MACs are 96-128 bits (12-16 bytes), but any length that
fits in the header of the segment being authenticated is allowed.
Because typical MACs are even-length, TCP-AO assumes so [RFC4306].
If a particular MAC is odd-length, it is padded.
>> An odd-length MAC MUST be padded with a single 0x00 byte on
transmit. Setting this pad byte is considered part of the
authentication algorithm.
>> An odd-length MAC MUST have a trailing 0x00 pad byte on o MAC: Message Authentication Field. Its contents are determined by
receipt. Checking this pad byte is considered part of the the particulars of the security association. Typical MACs are 96-
authentication algorithm. 128 bits (12-16 bytes), but any length that fits in the header of
the segment being authenticated is allowed. Because the KeyID is
one byte, it may be useful to have odd-length MACs (e.g., to
select an odd number of bytes of a computed even-length MAC).
When the Length is odd, a key identifier (KeyID) is included in o KeyID: The last byte of the option is a KeyID field. The KeyID is
the last byte of the option. The KeyID is used to support used to support efficient key rollover during a connection and/or
efficient key rollover during a connection and/or to help with key to help with key coordination during connection establishment, and
coordination during connection establishment, and will be will be discussed further in Sections 4.
discussed further in Sections 3.
>> TCP-AO MUST support TBD-WG-MACS; other MACs MAY be supported >> TCP-AO MUST support TBD-WG-MACS; other MACs MAY be supported
[RFC2403]. [RFC2403].
>> A single TCP segment MUST NOT have more than one TCP-AO option. >> A single TCP segment MUST NOT have more than one TCP-AO option.
The MAC is computed over the following fields in the following order: The MAC is computed over the following fields in the following order:
1. the TCP pseudoheader: IP source and destination addresses, 1. the TCP pseudoheader: IP source and destination addresses,
protocol number and segment length, all in network byte order, protocol number and segment length, all in network byte order,
skipping to change at page 11, line 13 skipping to change at page 10, line 50
[RFC793][RFC2460]: [RFC793][RFC2460]:
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Source Address | | Source Address |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Destination Address | | Destination Address |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| zero | Proto | TCP Length | | zero | Proto | TCP Length |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
Figure 5 TCP IPv4 pseudoheader [RFC793] Figure 3 TCP IPv4 pseudoheader [RFC793]
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| | | |
+ + + +
| | | |
+ Source Address + + Source Address +
| | | |
+ + + +
| | | |
+ + + +
+--------+--------+--------+--------+ +--------+--------+--------+--------+
skipping to change at page 11, line 38 skipping to change at page 11, line 27
+ Destination Address + + Destination Address +
| | | |
+ + + +
| | | |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Upper-Layer Packet Length | | Upper-Layer Packet Length |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| zero | Next Header | | zero | Next Header |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
Figure 6 TCP IPv6 pseudoheader [RFC2460] Figure 4 TCP IPv6 pseudoheader [RFC2460]
2. the TCP header, by default including options, and where the TCP 2. the TCP header, by default including options, and where the TCP
checksum and TCP-AO MAC fields are set to zero, all in network checksum and TCP-AO MAC fields are set to zero, all in network
byte order byte order
3. TCP data, in network byte order 3. TCP data, in network byte order
Note that the connection key is not included here; we expect that the Note that the connection key is not included here; we expect that the
MAC algorithm will indicate how to use the key, e.g., as HMACs do in MAC algorithm will indicate how to use the key, e.g., as HMACs do in
general [RFC2104][RFC2403]. general [RFC2104][RFC2403].
TCP-AO by default includes the TCP options because these options are TCP-AO by default includes the TCP options because these options are
intended to be end-to-end and some are required for proper TCP intended to be end-to-end and some are required for proper TCP
operation (e.g., SACK, timestamp, large windows). Middleboxes that operation (e.g., SACK, timestamp, large windows). Middleboxes that
alter TCP options en-route are a kind of attack and would be alter TCP options en-route are a kind of attack and would be
successfully detected by TCP-AO. In cases where the configuration of successfully detected by TCP-AO. In cases where the configuration of
the connection's security association state indicates otherwise, the the connection's security association state indicates otherwise, the
TCP options can be excluded from the MAC calculation. TCP options can be excluded from the MAC calculation. When options
are excluded, all options - including TCP-AO - are skipped over
during the MAC calculation (rather than being zeroed).
The TCP-AO option does not indicate the MAC algorithm either The TCP-AO option does not indicate the MAC algorithm either
implicitly (as with TCP MD5) or explicitly. The particular algorithm implicitly (as with TCP MD5) or explicitly. The particular algorithm
used is considered part of the configuration state of the used is considered part of the configuration state of the
connection's security association and is managed separately (see connection's security association and is managed separately (see
Section 3). Section 4).
3. Security Association Management MACs typically benefit from a per-connection nonce, notably in
avoiding the impact of key reuse. The presence of TCP's pair of
Initial Sequence Numbers presents a nonce that may be useful in that
case. Such a nonce could be computed as the concatenation of the ISNs
(initiator, responder), and the socket pair (addresses, ports):
o Nonce = ISN_i, ISN_r, IP_address_i, IP_address_r, port_i, port_r
The initial SYN would not know ISN_r, so that packet's nonce would
use ISN_r = 0. Use of these nonces avoids the need to avoid key reuse
on a per connection basis.
>> ISN and socket pair nonces MUST be used to generate unique per-
session keys.
4. Security Association Management
TCP-AO relies on a TCP Security Association Database (TSAD). TSAD TCP-AO relies on a TCP Security Association Database (TSAD). TSAD
entries are assumed to exist at the endpoints where TCP-AO is used, entries are assumed to exist at the endpoints where TCP-AO is used,
in advance of the connection: in advance of the connection:
1. TCP connection identifier (ID), i.e., socket pair - IP source 1. TCP connection identifier (ID), i.e., socket pair - IP source
address, IP destination address, TCP source port, and TCP address, IP destination address, TCP source port, and TCP
destination port [RFC793]. TSAD entries are uniquely determined by destination port [RFC793]. TSAD entries are uniquely determined by
their TCP connection ID, which is used to index those entries. their TCP connection ID, which is used to index those entries.
>> There MUST be no more than one matching TSAD entry per >> There MUST be no more than one matching TSAD entry per
direction for a TCP connection ID. direction for a TCP connection ID.
2. For each of inbound (for received TCP segments) and outbound (for 2. For each of inbound (for received TCP segments) and outbound (for
sent TCP segments) directions for this connection (except as sent TCP segments) directions for this connection (except as
noted): noted):
a. TCP option Kind exclusion list. A list of TCP option Kind a. TCP option exclusion flag. When 0, this flag allows default
values, indicating that TCP options are excluded from all MAC operation, i.e., TCP options are When 1, all options
calculations. When empty, all TCP options are included. The (including TCP-AO) are excluded from all MAC calculations
special value 0x00, normally indicating the end of the TCP (skipped over, not simply zeroed).
options list, indicates that all options are excluded (rather
than indicating them all).
>> The TCP option Kind exclusion list MUST default to empty >> The TCP option exclusion flag MUST default to 0 (i.e.,
(i.e., no options excluded). options not excluded).
>> The TCP option Kind exclusion list MUST NOT change during a >> The TCP option flag list MUST NOT change during a TCP
TCP connection. connection.
b. An ordered list of zero or more connection key tuples. Each b. An ordered list of zero or more connection key tuples. Each
tuple is defined as the set <[KeyID], MAC type, key length, tuple is defined as the set <KeyID, MAC type, key length,
connection key> as follows: connection key> as follows:
>> TSAD key tuple components MUST NOT change during a >> TSAD key tuple components MUST NOT change during a
connection. connection.
>> The set of TSAD key tuples MAY change during a connection, >> The set of TSAD key tuples MAY change during a connection,
but KeyIDs of those tuples MUST NOT overlap. I.e., tuple but KeyIDs of those tuples MUST NOT overlap. I.e., tuple
parameter changes MUST be accompanied by key changes. parameter changes MUST be accompanied by key changes.
i. KeyID (optional). A single byte used to differentiate i. KeyID. A single byte used to differentiate overlapping
overlapping Connection keys. Connection keys.
>> If the KeyID is not present for any key tuple, it MUST
be the only key tuple.
>> When an KeyID not used, the sender MUST use the key
from the first key tuple returned, and the receiver MUST
try all key tuples in order until one succeeds.
>> A TSAD implementation MUST support at least two KeyIDs >> A TSAD implementation MUST support at least two KeyIDs
per connection per direction, and MAY support up to 256. per connection per direction, and MAY support up to 256.
>> A KeyID MAY have the value of 0. >> A KeyID MAY have any value, 0-255 inclusive.
ii. MAC type. Indicates the MAC used for this connection, as ii. MAC type. Indicates the MAC used for this connection, as
per IKEv2 Transform Type 3 [RFC4306]. This includes the per IKEv2 Transform Type 3 [RFC4306]. This includes the
MAC algorithm (e.g., HMAC-MD5, HMAC-SHA1, UMAC, etc.) and MAC algorithm (e.g., HMAC-MD5, HMAC-SHA1, UMAC, etc.) and
the length of the MAC as truncated to (e.g., 96, 128, the length of the MAC as truncated to (e.g., 96, 128,
etc.). etc.).
>> A MAC type of NONE MUST be supported, to indicate that >> A MAC type of "NONE" MUST be supported, to indicate
authentication is not used in this direction; this allows that authentication is not used in this direction; this
asymmetric use of TCP-AO. allows asymmetric use of TCP-AO.
>> At least one direction (inbound/outbound) SHOULD have >> At least one direction (inbound/outbound) SHOULD have
a non-NONE MAC in practice, but this MUST NOT be strictly a non-"NONE" MAC in practice, but this MUST NOT be
required by an implementation. strictly required by an implementation.
>> When the outbound MAC is set to values other than >> When the outbound MAC is set to values other than
NONE, TCP-AO MUST occur in every outbound TCP segment for "NONE", TCP-AO MUST occur in every outbound TCP segment
that connection; when set to NONE or when no tuple for that connection; when set to NONE or when no tuple
exists, TCP-AO MUST NOT occur in those segments. exists, TCP-AO MUST NOT occur in those segments.
>> When the inbound MAC is set to values other than NONE, >> When the inbound MAC is set to values other than
TCP-AO MUST occur in every inbound TCP segment for that "NONE", TCP-AO MUST occur in every inbound TCP segment
connection; when set to NONE or when no tuple exists, for that connection; when set to "NONE" or when no tuple
TCP-AO SHOULD NOT be added to those segments, but MAY exists, TCP-AO SHOULD NOT be added to those segments, but
occur and MUST be ignored. MAY occur and MUST be ignored.
iii. Key length. A byte indicating the length of the iii. Key length. A byte indicating the length of the
connection key in bytes. connection key in bytes.
iv. Connection key. A byte sequence used for connection iv. Connection key. A byte sequence used for connection
keying, this may be derived from a separate shared key by keying, this may be derived from a separate shared key by
an external protocol over a separate channel. This an external protocol over a separate channel. This
sequence is used in network standard byte order in MAC sequence is used in network standard byte order in MAC
calculations. calculations.
It is anticipated that TSAD entries for TCP connections in states It is anticipated that TSAD entries for TCP connections in states
other than CLOSED can be stored in the TCP Control Block (TCB) or in other than CLOSED can be stored in the TCP Control Block (TCB) or in
a separate database (see Section 5.1 for notes on the latter); TSAD a separate database (see Section 6.1 for notes on the latter); TSAD
entries for pending connections (in passive or active OPEN) may be entries for pending connections (in passive or active OPEN) may be
stored in a separate database. This means that in a single host there stored in a separate database. This means that in a single host there
should be only a single database which is consulted by all pending should be only a single database which is consulted by all pending
connections, the same way that there is only one set of TCBs. connections, the same way that there is only one set of TCBs.
Multiple databases could be used to support virtual hosts, i.e., Multiple databases could be used to support virtual hosts, i.e.,
groups of interfaces. groups of interfaces.
Note that TSAD and the TCP-AO fields may omit use of the KeyID on a Note that the TCP-AO fields omit an explicit algorithm ID; that
per-connection configuration basis; the TCP connection ID already
uniquely specifies the TSAD entry, so a separate field is not needed
to specify a key unless key overlap during rekeying is supported or
is needed for key coordination during connection establishment (see
Section 5). The TCP-AO fields omit an explicit algorithm ID; that
algorithm is already specified by the TCP connection ID and stored in algorithm is already specified by the TCP connection ID and stored in
the TSAD. the TSAD.
Also note that this document does not address how TSAD entries are Also note that this document does not address how TSAD entries are
created by users/processes; it specifies how they must be destroyed created by users/processes; it specifies how they must be destroyed
corresponding to connection states, but users/processes may destroy corresponding to connection states, but users/processes may destroy
entries as well. It is presumed that a TSAD entry affecting a entries as well. It is presumed that a TSAD entry affecting a
particular connection cannot be destroyed during an active connection particular connection cannot be destroyed during an active connection
- or, equivalently, that its parameters are copied to TSAD entries - or, equivalently, that its parameters are copied to TSAD entries
local to the connection (i.e., instantiated) and so changes would local to the connection (i.e., instantiated) and so changes would
affect only new connections. The TSAD could be managed by a separate affect only new connections. The TSAD could be managed by a separate
application protocol, and can be stored in a separate database if application protocol, and can be stored in a separate database if
desired. desired.
4. TCP-AO Interaction with TCP 5. TCP-AO Interaction with TCP
The following is a description of how TCP-AO affects various TCP The following is a description of how TCP-AO affects various TCP
states, segments, events, and interfaces. This description is states, segments, events, and interfaces. This description is
intended to augment the description of TCP as provided in RFC793 intended to augment the description of TCP as provided in RFC793
[RFC793]. [RFC793].
4.1. User Interface 5.1. User Interface
The TCP user interface supports active and passive OPEN, SEND, The TCP user interface supports active and passive OPEN, SEND,
RECEIVE, CLOSE, STATUS and ABORT commands. RECEIVE, CLOSE, STATUS and ABORT commands.
>> TCP OPEN, or the sequence of commands that configure a connection >> TCP OPEN, or the sequence of commands that configure a connection
to be in the active or passive OPEN state, MUST be augmented so that to be in the active or passive OPEN state, MUST be augmented so that
a TSAD entry can be configured. a TSAD entry can be configured.
>> New TSAD entries MUST be checked against a table of previously Users are advised to not inappropriately reuse keys [RFC3562]. As
used TSAD entries, and key reuse MUST be prohibited. noted in Section 3.2, this is accomplished in TCP-AO by the use of
unique per-connection nonces in conjunction with conventional keys.
Users are advised to not inappropriately reuse keys [RFC3562].
>> TCP STATUS SHOULD be augmented to allow the TSAD entry of a >> TCP STATUS SHOULD be augmented to allow the TSAD entry of a
current or pending connection to be read (for confirmation). current or pending connection to be read (for confirmation).
>> TCP STATUS MUST allow TSAD entries for ongoing TCP connections >> A TCP-AO implmentation MUST allow TSAD entries for ongoing TCP
(i.e., not in the CLOSED state) to be modified. Parameters not used connections (i.e., not in the CLOSED state) to be modified.
to index a connection MAY be modified; parameters used to index a Parameters not used to index a connection MAY be modified; parameters
connection MUST NOT be modified. used to index a connection MUST NOT be modified.
TSAD entries for TCP connections not in the CLOSED state are deleted TSAD entries for TCP connections not in the CLOSED state are deleted
indirectly using the CLOSE or ABORT commands. This avoids key reuse, indirectly using the CLOSE or ABORT commands.
which could contribute to packet replays..
>> Use of CLOSE or ABORT MUST retain the TSAD entry in a table to
assist with checking for key reuse.
This entry may correspond to one of the wait states of TCP (FIN-WAIT-
1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, or TIME-WAIT), or may
be stored separately (i.e., in the key reuse table, for connections
proceeding rapidly to CLOSED). The size of this key reuse table and
duration of retained entries is up to the user, where we again advise
the application of known key management principles [RFC3562].
TCP SEND and RECEIVE are not affected by TCP-AO. TCP SEND and RECEIVE are not affected by TCP-AO.
4.2. TCP States and Transitions 5.2. TCP States and Transitions
TCP includes the states LISTEN, SYN-SENT, SYN-RECEIVED, ESTABLISHED, TCP includes the states LISTEN, SYN-SENT, SYN-RECEIVED, ESTABLISHED,
FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and
CLOSED. CLOSED.
>> A TSAD entry MAY be associated with any TCP state. >> A TSAD entry MAY be associated with any TCP state.
>> A TSAD entry MAY underspecify the TCP connection for the LISTEN >> A TSAD entry MAY underspecify the TCP connection for the LISTEN
state. Such an entry MUST NOT be used for more than one connection state. Such an entry MUST NOT be used for more than one connection
progressing out of the LISTEN state. progressing out of the LISTEN state.
4.3. TCP Segments 5.3. TCP Segments
TCP includes control (at least one of SYN, FIN, RST flags set) and TCP includes control (at least one of SYN, FIN, RST flags set) and
data (none of SYN, FIN, or RST flags set) segments. Note that some data (none of SYN, FIN, or RST flags set) segments. Note that some
control segments can include data (e.g., SYN). control segments can include data (e.g., SYN).
>> All TCP segments MUST be checked against the TSAD for matching TCP >> All TCP segments MUST be checked against the TSAD for matching TCP
connection IDs. connection IDs.
>> TCP segments matching TSAD entries with non-NULL MACs without TCP- >> TCP segments matching TSAD entries with non-NULL MACs without TCP-
AO, or with TCP-AO and whose MACs and/or KeyIDs (the latter when in AO, or with TCP-AO and whose MACs and KeyIDs do not validate MUST be
use) do not validate MUST be silently discarded. silently discarded.
>> TCP segments with TCP-AO but not matching TSAD entries MUST be >> TCP segments with TCP-AO but not matching TSAD entries MUST be
silently accepted; this is required for equivalent function with TCPs silently accepted; this is required for equivalent function with TCPs
not implementing TCP-AO. not implementing TCP-AO.
>> Silent discard events SHOULD be signaled to the user as a warning, >> Silent discard events SHOULD be signaled to the user as a warning,
and silent accept events MAY be signaled to the user as a warning. and silent accept events MAY be signaled to the user as a warning.
Both warnings, if available, MUST be accessible via the STATUS Both warnings, if available, MUST be accessible via the STATUS
interface. Either signal MAY be asynchronous, but if so they MUST be interface. Either signal MAY be asynchronous, but if so they MUST be
rate-limited. Either signal MAY be logged; logging SHOULD allow rate- rate-limited. Either signal MAY be logged; logging SHOULD allow rate-
limiting as well. limiting as well.
All TCP-AO processing occurs between the interface of TCP and IP; for All TCP-AO processing occurs between the interface of TCP and IP; for
incoming segments, this occurs after validation of the TCP checksum. incoming segments, this occurs after validation of the TCP checksum.
For outgoing segments, this occurs before computation of the TCP For outgoing segments, this occurs before computation of the TCP
checksum. checksum.
skipping to change at page 17, line 19 skipping to change at page 16, line 25
All TCP-AO processing occurs between the interface of TCP and IP; for All TCP-AO processing occurs between the interface of TCP and IP; for
incoming segments, this occurs after validation of the TCP checksum. incoming segments, this occurs after validation of the TCP checksum.
For outgoing segments, this occurs before computation of the TCP For outgoing segments, this occurs before computation of the TCP
checksum. checksum.
Note that the TCP-AO option is not negotiated. It is the Note that the TCP-AO option is not negotiated. It is the
responsibility of the receiver to determine when TCP-AO is required responsibility of the receiver to determine when TCP-AO is required
and to enforce that requirement. and to enforce that requirement.
4.4. Sending TCP Segments 5.4. Sending TCP Segments
The following procedure describes the modifications to TCP to support The following procedure describes the modifications to TCP to support
TCP-AO when a segment departs. TCP-AO when a segment departs.
1. Check the segment's TCP connection ID against the TSAD 1. Check the segment's TCP connection ID against the TSAD
2. If there is NO TSAD entry, omit the TCP-AO option. Proceed with 2. If there is NO TSAD entry, omit the TCP-AO option. Proceed with
computing the TCP checksum and transmit the segment. computing the TCP checksum and transmit the segment.
3. If there is a TSAD entry with zero key tuples, omit the TCP-AO 3. If there is a TSAD entry with zero key tuples, omit the TCP-AO
skipping to change at page 17, line 41 skipping to change at page 16, line 47
segment. segment.
4. If there is a TSAD entry and a key tuple and the outgoing MAC is 4. If there is a TSAD entry and a key tuple and the outgoing MAC is
NONE, omit the TCP-AO option. Proceed with computing the TCP NONE, omit the TCP-AO option. Proceed with computing the TCP
checksum and transmit the segment. checksum and transmit the segment.
5. If there is a TSAD entry and a key tuple and the outgoing MAC is 5. If there is a TSAD entry and a key tuple and the outgoing MAC is
not NONE: not NONE:
a. Augment the TCP header with the TCP-AO, inserting the a. Augment the TCP header with the TCP-AO, inserting the
appropriate Length and KeyID (the latter only if in use for appropriate Length and KeyID based on the indexed TSAD entry.
this connection) based on the indexed TSAD entry. Update the Update the TCP header length accordingly.
TCP header length accordingly.
b. Compute the MAC using the indexed TSAD entry and data from the b. Compute the MAC using the indexed TSAD entry and data from the
segment as specified in Section 2.2, including the TCP segment as specified in Section 3.2, including the TCP
pseudoheader and TCP header. pseudoheader and TCP header. Include or exclude the options as
indicated by the TSAD entry's TCP option exclusion flag.
Note that excluded options (if indicated in the TSAD) are
deleted (rather than zeroed) when used as input to the MAC
calculation. Deletion allows options inserted post-MAC (e.g.,
by middleboxes) to be correctly removed by the exclusion list.
c. Insert the MAC in the TCP-AO field. c. Insert the MAC in the TCP-AO field.
d. Proceed with computing the TCP checksum on the outgoing packet d. Proceed with computing the TCP checksum on the outgoing packet
and transmit the segment. and transmit the segment.
4.5. Receiving TCP Segments 5.5. Receiving TCP Segments
The following procedure describes the modifications to TCP to support The following procedure describes the modifications to TCP to support
TCP-AO when a segment arrives. TCP-AO when a segment arrives.
1. Check the segment's TCP connection ID against the TSAD. 1. Check the segment's TCP connection ID against the TSAD.
2. If there is NO TSAD entry, proceed with TCP processing. 2. If there is NO TSAD entry, proceed with TCP processing.
3. If there is a TSAD entry with zero key tuples, proceed with TCP 3. If there is a TSAD entry with zero key tuples, proceed with TCP
processing. processing.
skipping to change at page 18, line 41 skipping to change at page 17, line 37
4. If there is a TSAD entry with a key tuple and the incoming MAC is 4. If there is a TSAD entry with a key tuple and the incoming MAC is
NONE, proceed with TCP processing. NONE, proceed with TCP processing.
5. If there is a TSAD entry with a key tuple and the incoming MAC is 5. If there is a TSAD entry with a key tuple and the incoming MAC is
not NONE: not NONE:
a. Check that the segment's TCP-AO Length matches the length a. Check that the segment's TCP-AO Length matches the length
indicated by the indexed TSAD. indicated by the indexed TSAD.
i. If Lengths differ, silently discard the segment. Log i. If Lengths differ, silently discard the segment. Log
and/or signal the event as indicated in Section 4.3. and/or signal the event as indicated in Section 5.3.
b. If the Length is odd, use the KeyID value to index the b. Use the KeyID value to index the appropriate key for this
appropriate key for this connection; if the length is zero, connection.
use the single key in the response.
i. If the TSAD has no entry corresponding to the segment's i. If the TSAD has no entry corresponding to the segment's
KeyID, silently discard the segment. KeyID, silently discard the segment.
c. Compute the segment's MAC using the indexed TSAD entry and c. Compute the segment's MAC using the indexed TSAD entry and
portions of the segment as indicated in Section 2.2. portions of the segment as indicated in Section 3.2.
Again, note that excluded options are ignored (rather than Again, if options are excluded (as per the TCP option
zeroed) when used as input to the MAC calculation. exclusion flag), they are skipped over (rather than zeroed)
when used as input to the MAC calculation.
i. If the computed MAC differs from the TCP-AO MAC field i. If the computed MAC differs from the TCP-AO MAC field
value, silently discard the segment. Log and/or signal value, silently discard the segment. Log and/or signal
the event as indicated in Section 4.3. the event as indicated in Section 5.3.
d. Proceed with TCP processing of the segment. d. Proceed with TCP processing of the segment.
It is suggested that TCP-AO implementations validate a segment's It is suggested that TCP-AO implementations validate a segment's
Length field before computing a MAC, to reduce the overhead incurred Length field before computing a MAC, to reduce the overhead incurred
by spoofed segments with invalid TCP-AO fields. by spoofed segments with invalid TCP-AO fields.
4.6. Impact on TCP Header Size 5.6. Impact on TCP Header Size
The TCP-AO option typically uses a total of 16-18 bytes of TCP header The TCP-AO option typically uses a total of 17-19 bytes of TCP header
space. TCP-AO is no larger than and typically 4 bytes smaller than space. TCP-AO is no larger than and typically 3 bytes smaller than
the TCP MD5 option (assuming a 96-bit MAC). Although TCP option space the TCP MD5 option (assuming a 96-bit MAC). Although TCP option space
is limited, we believe TCP-AO is consistent with the desire to is limited, we believe TCP-AO is consistent with the desire to
authenticate TCP at the connection level for similar uses as were authenticate TCP at the connection level for similar uses as were
intended by TCP MD5. intended by TCP MD5.
5. Key Establishment and Duration Issues 6. Key Establishment and Duration Issues
The TCP-AO option does not provide a mechanism for connection key The TCP-AO option does not provide a mechanism for connection key
negotiation or parameter negotiation (MAC algorithm, length, or use negotiation or parameter negotiation (MAC algorithm, length, or use
of the TCP-AO option) or rekeying during a connection. We assume out- of the TCP-AO option) or rekeying during a connection. We assume out-
of-band mechanisms for key establishment, parameter negotiation, and of-band mechanisms for key establishment, parameter negotiation, and
rekeying. This separation of key use from key management is similar rekeying. This separation of key use from key management is similar
to that in the IPsec security suite [RFC4301][RFC4306]. to that in the IPsec security suite [RFC4301][RFC4306].
We encourage users of TCP-AO to apply known techniques for generating We encourage users of TCP-AO to apply known techniques for generating
appropriate keys, including the use of reasonable connection key appropriate keys, including the use of reasonable connection key
lengths, limited connection key sharing, and limiting the duration of lengths, limited connection key sharing, and limiting the duration of
connection key use [RFC3562]. connection key use [RFC3562]. This also includes the use of per-
connection nonces, as suggested in Section 3.2.
TCP-AO supports rekeying in which new keys are negotiated out-of- TCP-AO supports rekeying in which new keys are negotiated out-of-
band, either via a protocol or a manual procedure [RFC4808]. New keys band, either via a protocol or a manual procedure [RFC4808]. New keys
use is coordinated using the out-of-band mechanism to update the TSAD use is coordinated using the out-of-band mechanism to update the TSAD
at both TCP endpoints. In the default case, where only a single key at both TCP endpoints. In the default case, where only a single key
is used at a time, the temporary use of invalid keys would result in is used at a time, the temporary use of invalid keys would result in
packets being dropped; TCP is already robust to such drops. Such packets being dropped; TCP is already robust to such drops. Such
drops may affect TCP's throughput temporarily, as a result TCP-AO drops may affect TCP's throughput temporarily, as a result TCP-AO
benefits from the use of congestion control support for temporary benefits from the use of congestion control support for temporary
path outages. path outages.
>> TCP-AO SHOULD be deployed in conjunction with support for >> TCP-AO SHOULD be deployed in conjunction with support for
selective acknowledgement (SACK), including support for multiple lost selective acknowledgement (SACK), including support for multiple lost
segments in the same round trip [RFC2018][RFC3517]. segments in the same round trip [RFC2018][RFC3517].
Note that TCP-AO's support for rekeying is designed to be minimal in Note that TCP-AO's support for rekeying is designed to be minimal in
the default case. Segments carry only enough context to identify the the default case. Segments carry only enough context to identify the
security association [RFC4301][RFC4306]. In TCP-AO, this context is security association [RFC4301][RFC4306]. In TCP-AO, this context is
provided by the socket pair (IP addresses and ports for source and provided by the socket pair (IP addresses and ports for source and
destination). In the default case, the key is identified only in the destination). The TSAD can contain multiple concurrent keys, where
TSAD, and coordinated by a separate mechanism not specified in TCP- the KeyID field is used to identify the key that corresponds to a
AO. In cases where such coordination is difficult, or where loss segment, to avoid the need for expensive trial-and-error testing of
during rekeying is inappropriate, the TSAD can contain multiple keys in sequence.
concurrent keys. Where multiple keys are used, the KeyID field is
used to identify the key that corresponds to a segment, to avoid the
need for expensive trial-and-error testing of keys in sequence.
The KeyID field may also be useful in coordinating keys for new The KeyID field is also useful in coordinating keys for new
connections. A TSAD may be configured that matches the unbound source connections. A TSAD may be configured that matches the unbound source
port, which would return a set of possible keys. The KeyID would then port, which would return a set of possible keys. The KeyID would then
indicate which key, allowing more efficient connection establishment; indicate which key, allowing more efficient connection establishment;
otherwise, the keys could be tried in sequence. See also Section 5.1. otherwise, the keys could have been tried in sequence. See also
Section 6.1.
Implementations are encouraged to keep keys in a suitably private Implementations are encouraged to keep keys in a suitably private
area. Users of TCP-AO are encouraged to use different keys for area. Users of TCP-AO are encouraged to use different keys for
inbound and outbound MACs on a given TCP connection. inbound and outbound MACs on a given TCP connection.
5.1. Implementing the TSAD as an External Database 6.1. Implementing the TSAD as an External Database
The TSAD implementation is considered external to TCP-AO. When an The TSAD implementation is considered external to TCP-AO. When an
external database is used, it would be useful to consider the external database is used, it would be useful to consider the
interface between TCP-AO and the TSAD. The following is largely a interface between TCP-AO and the TSAD. The following is largely a
restatement of information in Section 3. restatement of information in Section 4.
The TSAD API is accessed during a connection as follows: The TSAD API is accessed during a connection as follows:
o TCP connection identifier (ID) (The socket pair, sent as 4 byte IP o TCP connection identifier (ID) (The socket pair, sent as 4 byte IP
source address, 4 byte IP destination address, 2 byte TCP source source address, 4 byte IP destination address, 2 byte TCP source
port, 2 byte TCP destination port). port, 2 byte TCP destination port).
o Direction indicator (sent as a single byte, 0x00 = inbound, 0x01 = o Direction indicator (sent as a single byte, 0x00 = inbound, 0x01 =
outbound) outbound)
o Number of bytes to be sent/received (two bytes); this is used on o Number of bytes to be sent/received (two bytes); this is used on
the send side to trigger bytecount-based KeyID changes, and on the the send side to trigger bytecount-based KeyID changes, and on the
receive side only for statistics or length-sensitive KeyID receive side only for statistics or length-sensitive KeyID
selection. selection.
o KeyID (single byte, optional as indicated by a flag elsewhere in >> TCP-AO implementations SHOULD change keys for a connection at
the TSAD) least every 2^31 bytes, to avoid resending segments with the same
TCP sequence number, data, and length under the same key.
o KeyID (single byte); this is provided only by a receiver (i.e.,
matching the KeyID of the received segment), where a sender would
leave this unspecified (and the call would return the appropriate
KeyID to use).
The call passes the number of bytes sent/received, and an indication The call passes the number of bytes sent/received, and an indication
of the direction (send/receive), to enable traffic-based key of the direction (send/receive), to enable traffic-based key
rollover. rollover.
The source port can be 'unbound', indicated by the value 0x0000. In The source port can be 'unbound', indicated by the value 0x0000. In
this case, the source port is considered a wildcard, and all this case, the source port is considered a wildcard, and all
corresponding TSAD entries (typically also indexed by the KeyID in corresponding TSAD entries (indexed by the KeyID) are returned as a
that case) are returned as a list. This feature is used during list. This feature is used during connection establishment.
connection establishment.
TSAD calls return the following parameters: TSAD calls return the following parameters:
o TCP Option exclusion list (a list of TCP option Kind bytes, with o TCP option exclusion flag (one byte, with 0x00 having the meaning
0x00 having the meaning "exclude all"). "exclude none" and 0x01 meaning "exclude all").
o An ordered list of zero or more connection key tuples: o An ordered list of zero or more connection key tuples:
<KeyID, MAC type, MAC length, connection key> <KeyID, MAC type, MAC length, connection key>
o KeyID (one byte, ignored if the KeyID is not present) o KeyID (one byte)
o MAC type (four bytes, an IKEv2 Transform Type 3 ID [RFC4306]) o MAC type (four bytes, an IKEv2 Transform Type 3 ID [RFC4306])
o Key length (one byte) o Key length (one byte)
o Connection key (byte sequence, indicating the key value) o Connection key (byte sequence, indicating the key value)
When the TSAD returns zero keys, it is indicating that there are no When the TSAD returns zero keys, it is indicating that there are no
currently valid keys for the connection. currently valid keys for the connection.
6. Interactions with TCP MD5 7. Interactions with TCP MD5
TCP-AO is intended to be deployed without regard for existing TCP MD5 TCP-AO is intended to be deployed without regard for existing TCP MD5
option support. option support.
>> A TCP implementation MUST NOT use both TCP-AO and TCP MD5 for a >> A TCP implementation MUST NOT use both TCP-AO and TCP MD5 for a
particular TCP connection, but MAY support TCP-AO and TCP MD5 particular TCP connection, but MAY support TCP-AO and TCP MD5
simultaneously for different connections. simultaneously for different connections.
The Kind value explicitly indicates which of TCP-AO or TCP MD5 is The Kind value explicitly indicates which of TCP-AO or TCP MD5 is
used for a particular connection in the TCP segments. used for a particular connection in TCP segments.
It is possible that the TSAD could be augmented to support TCP MD5, It is possible that the TSAD could be augmented to support TCP MD5,
although use of a TSAD-like system is not described in RFC2385. although use of a TSAD-like system is not described in RFC2385.
It is possible to require TCP-AO for a connection or TCP MD5, but it It is possible to require TCP-AO for a connection or TCP MD5, but it
is not possible to require 'either'. Note that when TCP MD5 is is not possible to require 'either'. Note that when TCP MD5 is
required on for a connection, it must be used [RFC2385]. This required on for a connection, it must be used [RFC2385]. This
prevents combined use of the two options for a given connection, to prevents combined use of the two options for a given connection, to
be determined by the other end of the connection. be determined by the other end of the connection.
7. Interactions with NAT/NAPT Devices 8. Interactions with NAT/NAPT Devices
TCP-AO assumes that NAT/NAPT traversal is handled in similar ways to TCP-AO can interoperate across NAT/NAPT devices, which modify the IP
IPsec [RFC2766][RFC3947]. I.e., traversing such a device requires the addresses, and may also modify TCP port numbers and/or TCP options.
use of a tunnel to avoid the NAT/NAPT from translating fields in the TCP options can be excluded on a per-connection basis.
TCP and IP headers TCP-AO uses in its MAC calculation. Such a tunnel
may need to coincide with the channel over which keys are exchanged,
as in IPsec NAT traversal [RFC3947].
8. Evaluation of Requirements Satisfaction IP addresses and port numbers would preferably be coordinated across
a NAT/NAPT device, such that the sender and receiver both know the IP
address and TCP port numbers of the received packet. In that case,
the sender computes the packet as it would be received, i.e., using
the receiver's version of the IP pseudoheader and TCP header.
Where such knowledge of the address and port translations are not
known, NAT/NAPT traversal can be handled in similar ways to IPsec
[RFC2766][RFC3947]. I.e., traversing such a device using a tunnel to
avoid the NAT/NAPT from translating fields in the TCP and IP headers
TCP-AO uses in its MAC calculation. Such a tunnel may need to
coincide with the channel over which keys are exchanged, as in IPsec
NAT traversal [RFC3947].
9. Evaluation of Requirements Satisfaction
TCP-AO satisfies all the current requirements for a revision to TCP TCP-AO satisfies all the current requirements for a revision to TCP
MD5, as indicated in [Be07] and under current developemt. This should MD5, as indicated in [Be07] and under current developemt. This should
not be a surprise, as the majority of the evolving requirements are not be a surprise, as the majority of the evolving requirements are
derived from its design. The following is a summary of those derived from its design. The following is a summary of those
requirements and notes where relevant. requirements and notes where relevant.
1. Protected Elements - see Section 2.2. 1. Protected Elements - see Section 3.2.
a. TCP pseudoheader, including IPv4 and IPv6 versions. Note that a. TCP pseudoheader, including IPv4 and IPv6 versions. Note that
we do not allow optional coverage because we present a we do not allow optional coverage because IP addresses define
solution that does not require such to interoperate with a connection. If they can be coordinated across a NAT/NAPT,
NAT/NAPT devices. the sender can compute the MAC based on the received values;
if not, a tunnel is required.
b. TCP header. Note that we do not allow port coverage to be b. TCP header. Note that we do not allow optional port coverage
optional because we present a solution that does not require because ports define a connection. If they can be coordinated
this to interoperate with NAT/NAPT devices. across a NAT/NAPT, the sender can compute the MAC based on the
received values; if not, a tunnel is required.
c. TCP options. Allows exclusion of any option desired except c. TCP options. Allows exclusion of TCP options from coverage, as
TCP-AO, as required. required.
d. TCP data. Done. d. TCP data. Done.
2. Option structure requirements 2. Option structure requirements
a. Privacy. TCP-AO exposes only the key index, MAC, and overall a. Privacy. TCP-AO exposes only the key index, MAC, and overall
option length. Note that short MACs could be obscured by using option length. Note that short MACs could be obscured by using
longer option lengths but specifying a short MAC length (this longer option lengths but specifying a short MAC length (this
is equivalent to a different MAC algorithm, and is specified is equivalent to a different MAC algorithm, and is specified
in the TSAD entry). See Section 2.2. in the TSAD entry). See Section 3.2.
b. Allow optional per connection. Done - see Sections 4.3, 4.4, b. Allow optional per connection. Done - see Sections 5.3, 5.4,
and 4.5. and 5.5.
c. Require non-optional. Done - see Sections 4.3, 4.4, and 4.5. c. Require non-optional. Done - see Sections 5.3, 5.4, and 5.5.
d. Standard parsing. Done - see Section 2.2. d. Standard parsing. Done - see Section 3.2.
e. Compatible with Large Windows. Done - see Section 2.2. The e. Compatible with Large Windows. Done - see Section 3.2. The
size of the option is intended to allow use with Large Windows size of the option is intended to allow use with Large Windows
and SACK. See also Section 1.1, which indicates that TCP-AO is and SACK. See also Section 1.1, which indicates that TCP-AO is
4 bytes shorter than TCP MD5 in the default case, assuming a 4 bytes shorter than TCP MD5 in the default case, assuming a
96-bit MAC. 96-bit MAC.
f. Compatible with SACK. Done - see Section 2.2. The size of the f. Compatible with SACK. Done - see Section 3.2. The size of the
option is intended to allow use with Large Windows and SACK. option is intended to allow use with Large Windows and SACK.
See also Section 5 regarding key management. See also Section See also Section 6 regarding key management. See also Section
1.1, which indicates that TCP-AO is 4 bytes shorter than TCP 1.1, which indicates that TCP-AO is 4 bytes shorter than TCP
MD5 in the default case. MD5 in the default case.
3. Cryptography requirements 3. Cryptography requirements
a. Baseline defaults. TCP-AO uses TBD-WG-MACS as the default, as a. Baseline defaults. TCP-AO uses TBD-WG-MACS as the default, as
noted in Section 2.2. noted in Section 3.2.
b. Good algorithms. TCP-AO uses TBD-WG-MACS as the default, but b. Good algorithms. TCP-AO uses TBD-WG-MACS as the default, but
does not otherwise specify the algorithms used. That would be does not otherwise specify the algorithms used. That would be
specified in the key management protocol, and should be specified in the key management protocol, and should be
limited there. limited there.
c. Algorithm agility. TCP-AO allows any desired algorithm, c. Algorithm agility. TCP-AO allows any desired algorithm,
subject to TCP option space limitations, as noted in Section subject to TCP option space limitations, as noted in Section
2.2. The TSAD allows separate connections to use different 3.2. The TSAD allows separate connections to use different
algorithms. algorithms.
d. Pre-TCP processing. Done - see Sections 4.3, 4.4, and 4.5. d. Pre-TCP processing. Done - see Sections 5.3, 5.4, and 5.5.
Note that pre-TCP processing is required, because TCP segments Note that pre-TCP processing is required, because TCP segments
cannot be discarded solely based on a combination of cannot be discarded solely based on a combination of
connection state and out-of-window checks; many such segments, connection state and out-of-window checks; many such segments,
although discarded, cause a host to respond with a replay of although discarded, cause a host to respond with a replay of
the last valid ACK, e.g. [RFC793]. the last valid ACK, e.g. [RFC793].
e. Parameter changes require key changes. TSAD parameters that e. Parameter changes require key changes. TSAD parameters that
should not change during a connection (TCP connection ID, should not change during a connection (TCP connection ID,
receiver TCP connection ID, TCP option exclusion list) cannot receiver TCP connection ID, TCP option exclusion list) cannot
change. Other parameters change only when a key is changed, change. Other parameters change only when a key is changed,
using the key tuple mechanism in the TSAD. See Section 3. using the key tuple mechanism in the TSAD. See Section 4.
4. Keying requirements. TCP-AO does not specify a key management 4. Keying requirements. TCP-AO does not specify a key management
system, but does indicate a proposed interface to the TSAD, system, but does indicate a proposed interface to the TSAD,
allowing a completely separate key system. allowing a completely separate key system.
a. Intraconnection rekeying. Supported by the KeyID and multiple a. Intraconnection rekeying. Supported by the KeyID and multiple
key tuples in a TSAD entry; see Section 3. key tuples in a TSAD entry; see Section 4.
b. Efficient rekeying. Supported by the KeyID. See Section 5. b. Efficient rekeying. Supported by the KeyID. See Section 6.
c. Automated and manual keying. Supported by the TSAD interface. c. Automated and manual keying. Supported by the TSAD interface.
See Section 5. See Section 6.
d. Key management agnostic. Supported by the TSAD interface. See d. Key management agnostic. Supported by the TSAD interface. See
Section 5.1. Section 6.1.
5. Expected constraints 5. Expected constraints
a. Silent failure. Done - see Sections 4.3, 4.4, and 4.5. a. Silent failure. Done - see Sections 5.3, 5.4, and 5.5.
b. At most one such option per segment. Done - see Section 2.2. b. At most one such option per segment. Done - see Section 3.2.
c. Outgoing all or none. Done - see Section 4.4. c. Outgoing all or none. Done - see Section 5.4.
d. Incoming all checked. Done - see Section 4.5. d. Incoming all checked. Done - see Section 5.5.
e. Non-interaction with TCP MD5. Done - see Section 6. e. Non-interaction with TCP MD5. Done - see Section 7.
f. Optional ICMP discard. Done - see Section 9. f. Optional ICMP discard. Done - see Section 10.
g. Allows use of NAT/NAPT devices. Done - see Section 7. g. Allows use of NAT/NAPT devices. Done - see Section 8.
h. Maintain TCP connection semantics, in which only the socket h. Maintain TCP connection semantics, in which only the socket
pair defines a TCP association and all its security pair defines a TCP association and all its security
parameters. Done - see Sections 3 and 7. parameters. Done - see Sections 4 and 8.
i. Try to avoid creating a CPU DOS attack opportunity. Done - see i. Try to avoid creating a CPU DOS attack opportunity. Done - see
Section 9. Section 10.
9. Security Considerations 10. Security Considerations
Use of TCP-AO, like use of TCP MD5 or IPsec, will impact host Use of TCP-AO, like use of TCP MD5 or IPsec, will impact host
performance. Connections that are known to use TCP-AO can be attacked performance. Connections that are known to use TCP-AO can be attacked
by transmitting segments with invalid MACs. Attackers would need to by transmitting segments with invalid MACs. Attackers would need to
know only the TCP connection ID and TCP-AO Length value to know only the TCP connection ID and TCP-AO Length value to
substantially impact the host's processing capacity. This is similar substantially impact the host's processing capacity. This is similar
to the susceptibility of IPsec to on-path attacks, where the IP to the susceptibility of IPsec to on-path attacks, where the IP
addresses and SPI would be visible. For IPsec, the entire SPI space addresses and SPI would be visible. For IPsec, the entire SPI space
(32 bits) is arbitrary, whereas for routing protocols typically only (32 bits) is arbitrary, whereas for routing protocols typically only
the source port (16 bits) is arbitrary. As a result, it would be the source port (16 bits) is arbitrary. As a result, it would be
skipping to change at page 26, line 44 skipping to change at page 25, line 47
CPU DOS attack, where the attacker sends false, random segments that CPU DOS attack, where the attacker sends false, random segments that
the receiver under attack expends substantial CPU effort to reject. the receiver under attack expends substantial CPU effort to reject.
In IPsec, such attacks are reduced by the use of a large Security In IPsec, such attacks are reduced by the use of a large Security
Parameter Index (SPI) and Sequence Number fields to partly validate Parameter Index (SPI) and Sequence Number fields to partly validate
segments before CPU cycles are invested validated the Integrity Check segments before CPU cycles are invested validated the Integrity Check
Value (ICV). In TCP-AO, the socket pair performs most of the function Value (ICV). In TCP-AO, the socket pair performs most of the function
of IPsec's SPI, and IPsec's Sequence Number, used to avoid replay of IPsec's SPI, and IPsec's Sequence Number, used to avoid replay
attacks, isn't needed due to TCP's Sequence Number, which is used to attacks, isn't needed due to TCP's Sequence Number, which is used to
reorder received segments. Unfortunately, it is not useful to reorder received segments. Unfortunately, it is not useful to
validate TCP's Sequence Number before performing a TCP-AO validate TCP's Sequence Number before performing a TCP-AO
authentication calculation, because many out-of-window segments still authentication calculation, because out-of-window segments can still
cause TCP protocol actions (e.g., ACK retransmission) [RFC793]. It is cause TCP protocol actions (e.g., ACK retransmission) [RFC793]. It is
similarly not useful to add a separate Sequence Number field to the similarly not useful to add a separate Sequence Number field to the
TCP-AO option, because doing so could cause a change in TCP's TCP-AO option, because doing so could cause a change in TCP's
behavior even when segments are valid. behavior even when segments are valid.
10. IANA Considerations 11. IANA Considerations
The TCP-AO option defines no new namespaces. The TCP-AO option defines no new namespaces.
The TCP-AO option uses the TCP option Kind value TCP-IANA-KIND, The TCP-AO option uses the TCP option Kind value TCP-IANA-KIND,
allocated by IANA from the TCP option Kind namespace. allocated by IANA from the TCP option Kind namespace.
To specify MAC algorithms, TCP-AO uses the 4-byte namespace of IKEv2 To specify MAC algorithms, TCP-AO uses the 4-byte namespace of IKEv2
Transform Type 3 IDs [RFC4306]. Transform Type 3 IDs [RFC4306].
[NOTE: The following to be removed prior to publication as an RFC] [NOTE: The following to be removed prior to publication as an RFC]
The TCP-AO option requires that IANA allocate a value from the TCP The TCP-AO option requires that IANA allocate a value from the TCP
option Kind namespace, to be replaced for TCP-IANA-KIND throughout option Kind namespace, to be replaced for TCP-IANA-KIND throughout
this document. this document.
11. Acknowledgments 12. Acknowledgments
This document was inspired by the revisions to TCP MD5 suggested by This document was inspired by the revisions to TCP MD5 suggested by
Brian Weis and Ron Bonica [Bo07][We05]. Russ Housley suggested Brian Weis and Ron Bonica [Bo07][We05]. Russ Housley suggested
L4/application layer management of the TSAD. The KeyID field was L4/application layer management of the TSAD. The KeyID field was
motivated by Steve Bellovin. Alfred Hoenes provided substantial motivated by Steve Bellovin. Eric Rescorla suggested the use of ISNs
feedback on this document. The document is the result of as nonces, and Brian Weis extended the nonce to incorporate the
entire connection ID. Alfred Hoenes, Charlie Kaufman, and Adam
Langley provided substantial feedback. The document is the result of
collaboration with the TCP Authentication Design team (tcp-auth-dt). collaboration with the TCP Authentication Design team (tcp-auth-dt).
This document was prepared using 2-Word-v2.0.template.dot. This document was prepared using 2-Word-v2.0.template.dot.
12. References 13. References
12.1. Normative References 13.1. Normative References
[RFC793] Postel, J., "Transmission Control Protocol," STD 007, RFC [RFC793] Postel, J., "Transmission Control Protocol," STD 007, RFC
793, Standard, Sept. 1981. 793, Standard, Sept. 1981.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP [RFC2018] Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP
Selective Acknowledgement Options", RFC 2018, Proposed Selective Acknowledgement Options", RFC 2018, Proposed
Standard, April 1996. Standard, April 1996.
[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, Best Current Requirement Levels", BCP 14, RFC 2119, Best Current
skipping to change at page 28, line 17 skipping to change at page 27, line 20
1998. 1998.
[RFC3517] Blanton, E., Allman, M., Fall, K., and L. Wang, "A [RFC3517] Blanton, E., Allman, M., Fall, K., and L. Wang, "A
Conservative Selective Acknowledgment (SACK)-based Loss Conservative Selective Acknowledgment (SACK)-based Loss
Recovery Algorithm for TCP", RFC 3517, Proposed Standard, Recovery Algorithm for TCP", RFC 3517, Proposed Standard,
April 2003. April 2003.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol," RFC [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol," RFC
4306, Proposed Standard, Dec. 2005. 4306, Proposed Standard, Dec. 2005.
12.2. Informative References 13.2. Informative References
[Be05] Bellovin, S., E. Rescorla, "Deploying a New Hash [Be05] Bellovin, S., E. Rescorla, "Deploying a New Hash
Algorithm," presented at the First NIST Cryptographic Hash Algorithm," presented at the First NIST Cryptographic Hash
Workshop, Oct. 2005. Workshop, Oct. 2005.
http://csrc.nist.gov/pki/HashWorkshop/2005/program.htm http://csrc.nist.gov/pki/HashWorkshop/2005/program.htm
[Be07] Eddy, W., (ed), S. Bellovin, J. Touch, R. Bonica, "Problem [Be07] Eddy, W., (ed), S. Bellovin, J. Touch, R. Bonica, "Problem
Statement and Requirements for a TCP Authentication Statement and Requirements for a TCP Authentication
Option," draft-bellovin-tcpsec-01, (work in progress), Jul. Option," draft-bellovin-tcpsec-01, (work in progress), Jul.
2007. 2007.
skipping to change at page 28, line 39 skipping to change at page 27, line 42
[Bu06] Burr, B., "NIST Cryptographic Standards Status Report," [Bu06] Burr, B., "NIST Cryptographic Standards Status Report,"
Invited talk at Internet 2 5th Annual PKI R&D Workshop, Invited talk at Internet 2 5th Annual PKI R&D Workshop,
April 2006. April 2006.
http://middleware.internet2.edu/pki06/proceedings/ http://middleware.internet2.edu/pki06/proceedings/
[Bo07] Bonica, R., et. al, "Authentication for TCP-based Routing [Bo07] Bonica, R., et. al, "Authentication for TCP-based Routing
and Management Protocols," draft-bonica-tcp-auth-06 , and Management Protocols," draft-bonica-tcp-auth-06 ,
(work in progress), Feb. 2007. (work in progress), Feb. 2007.
[Go07] Gont, F., "ICMP attacks against TCP," draft-ietf-tcpm-icmp- [Go07] Gont, F., "ICMP attacks against TCP," draft-ietf-tcpm-icmp-
attacks-02, (work in progress), May 2007. attacks-03, (work in progress), Mar. 2008.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC-1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC-1321,
Informational, April 1992. Informational, April 1992.
[RFC2104] Krawczyk, H., Bellare, M., Canetti, R., "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., Canetti, R., "HMAC: Keyed-
Hashing for Message Authentication," RFC 2104, Hashing for Message Authentication," RFC 2104,
Informational, Feb. 1997. Informational, Feb. 1997.
[RFC2766] Tsirtsis, G., Srisuresh, P., "Network Address Translation - [RFC2766] Tsirtsis, G., Srisuresh, P., "Network Address Translation -
Protocol Translation (NAT-PT)," RFC 2766, Proposed Protocol Translation (NAT-PT)," RFC 2766, Proposed
skipping to change at page 30, line 20 skipping to change at page 29, line 20
URL: http://www.psg.com/~mankin/ URL: http://www.psg.com/~mankin/
Ronald P. Bonica Ronald P. Bonica
Juniper Networks Juniper Networks
2251 Corporate Park Drive 2251 Corporate Park Drive
Herndon, VA 20171 Herndon, VA 20171
U.S.A. U.S.A.
Email: rbonica@juniper.net Email: rbonica@juniper.net
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
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made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
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skipping to change at page 30, line 43 skipping to change at line 1349
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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Disclaimer of Validity
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
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