TCPM WG J. Touch
Internet Draft USC/ISI
Expires: December 2006 A. Mankin
June 9, 2006
The TCP Simple Authentication Option
draft-touch-tcpm-tcp-simple-auth-00.txt
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Abstract
This document specifies a TCP Simple Authentication Option (TCP-SA)
which is intended to replace the TCP MD5 Signature option of RFC-2385
(TCP/MD5). TCP-SA specifies the use of stronger HMAC-based hashes and
provides more details on the association of security associations
with TCP connections. TCP-SA assumes that rekeying is supported by
restarting the TCP connection, and so omits in-band parameter
negotiation, session key establishment, and rekeying support; where
such features are desired, use of the IPsec suite is recommended.
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The result is intended to be a simple modification to support current
infrastructure uses of TCP/MD5, such as to protect BGP and LDP, to
support a larger set of hashes with minimal other system and
operational changes. TCP-SA requires no new option identifier, though
it is intended to be mutually exclusive with TCP/MD5 on a given TCP
connection.
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
1. Introduction...................................................3
1.1. Executive Summary.........................................3
1.2. Summary of RFC-2119 Requirements..........................4
2. The TCP Simple Authentication Option...........................5
2.1. Review of TCP/MD5 Option..................................5
2.2. TCP-SA Option.............................................5
3. Security Association Management................................7
4. TCP-SA Interaction with TCP....................................9
4.1. User Interface............................................9
4.2. TCP States and Transitions................................9
4.3. TCP Segments.............................................10
4.4. Sending TCP Segments.....................................10
4.5. Receiving TCP Segments...................................11
4.6. Impact on TCP Header Size................................12
5. Key Establishment and Duration Issues.........................12
6. Use of TCP-SA with Routing Protocols..........................13
7. Interactions with TCP/MD5.....................................13
8. Security Considerations.......................................14
9. IANA Considerations...........................................15
10. Conclusions..................................................15
11. Acknowledgments..............................................15
12. References...................................................15
12.1. Normative References....................................15
12.2. Informative References..................................16
Author's Addresses...............................................17
Intellectual Property Statement..................................17
Disclaimer of Validity...........................................18
Copyright Statement..............................................18
Acknowledgment...................................................18
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1. Introduction
The TCP MD5 Signature (TCP/MD5) is a TCP option that authenticates
TCP segments, including the TCP pseudo-header, TCP header, and TCP
data. It was developed to protect BGP sessions from spoofed TCP
segments which could affect BGP data or the robustness of the TCP
connection itself.
There have been many recently-documented concerns about TCP/MD5. Its
use of a simple keyed hash for authentication is problematic because
there have been escalating attacks on the algorithm itself [Be05]
[Bu06]. TCP/MD5 also lacks both key management and algorithm
agility. This document proposes to add the latter, but suggests that
TCP should not be the framework for cryptographic key management.
This document updates the TCP/MD5 option to become a more general TCP
Simple Authentication Option (TCP-SA), to support the use of other,
stronger hash functions and to provide a more structured
recommendation on external key management.
This document is not intended to replace the use of the IPsec suite
(IPsec and IKE) to protect TCP connections [RFC4301][RFC4306]. In
fact, we recommend the use of IPsec and IKE, especially where
parameter negotiation, session key negotiation, or intra-connection
rekeying are desired.
1.1. Executive Summary
This document updates TCP/MD5 as follows [RFC2385]:
o Reuses TCP/MD5's option Kind (=19), but allows TCP/MD5 to continue
to be used for other connections.
o Replaces signed MD5 with HMAC-MD5-96, and allows other MACs at the
implementer's discretion.
o Does not allow rekeying during a TCP connection (although how to
achieve this is not specified in RFC2385, notably in its impact to
TCP windowing).
o Provides more detail in how this option interacts with TCP's
states, event processing, and user interface.
o Proposed option is 4 bytes shorter (14 bytes overall, rather than
18) in the default case (HMAC-MD5-96).
This document differs from currently competing proposals to update
TCP/MD5 as follows [Bo05][We06]:
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o Does not require a new TCP option Kind value.
o Does not support rekeying during a connection.
o Does not support dynamic parameter negotiation.
o Does not require additional timers.
o Always authenticates the TCP options as well as the segment
pseudoheader, header, and data.
o Provides more detail in how this option interacts with TCP's
states, event processing, and user interface.
o Proposed option is 2 bytes shorter (14 bytes overall, rather than
16) in the default case (HMAC-MD5-96)
o Does not expose the MAC algorithm in the header.
o Does not require a key ID.
This document differs from an IPsec/IKE solution as follows
[RFC4301][RFC4306]
o Does not support rekeying during a connection.
o Does not support dynamic parameter negotiation.
o Does not support establishment of a per-connection key.
o Does not require a key ID (SPI).
o Does not protect from replay attacks.
o Forces a change of connection key when a connection restarts, even
when reusing a TCP socket pair (IP addresses and port numbers).
o Does not support encryption.
o Does not authenticate ICMP messages (some may be authenticated in
IPsec, depending on the configuration).
1.2. Summary of RFC-2119 Requirements
[NOTE: a summary will be placed here prior to last call]
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2. The TCP Simple Authentication Option
The TCP Simple Authentication Option (TCP-SA) re-uses the Kind value
currently assigned to TCP/MD5.
2.1. Review of TCP/MD5 Option
For review, the TCP/MD5 option is shown in Figure 1.
+---------+---------+-------------------+
| Kind=19 |Length=18| MD5 digest... |
+---------+---------+-------------------+
| |
+---------------------------------------+
| |
+---------------------------------------+
| |
+-------------------+-------------------+
| |
+-------------------+
Figure 1 Current TCP MD5 Option [RFC2385]
In the current TCP/MD5 option, the length is fixed, and the MD5
digest occupies 16 bytes following the Kind and Length fields, using
the full MD5 digest of 128 bits [RFC1321].
The current TCP/MD5 option specifies the use of the MD5 digest
calculation over the following values in the following order:
1. the TCP pseudoheader (IP source and destination addresses,
protocol number, and segment length)
2. TCP header excluding options and checksum
3. TCP data
4. connection key
2.2. TCP-SA Option
The new TCP-SA option is intended to be a superset of the TCP/MD5
option. TCP-SA reuses the same Kind and Length fields, and is shown
in Figure 2.
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+---------+---------+-----------------...
| Kind=19 | Len=var | MAC... ...
+---------+---------+-----------------...
Figure 2 Proposed TCP-SA Option
The TCP-SA defines the following fields:
o Kind: An unsigned field indicating the TCP Option. TCP-SA reuses
the Kind value=19. Because of how keys are managed (see Section
3), an endpoint will not use TCP-SA for the same connection where
TCP/MD5 is used, and so there would be no confusion as to how to
interpret incoming Kind=19 segments.
o Length: An unsigned 8-bit field indicating the length of the TCP-
SA option in bytes, including the Kind and Length fields.
>> The Length MUST be greater than or equal to 2.
>> The Length value MUST be consistent with the TCP header length.
Values of 2 and other small values are of dubious utility but not
specifically prohibited.
o MAC: The MAC is a message authentication code. Typical MACs are
96-128 bits (12-16 bytes), but any length that fits in the header
of the segment being authenticated is allowed.
>> TCP-SA MUST support HMAC-MD5-96; other MACs MAY be supported
[RFC2403].
>> A single TCP segment MUST NOT have more than one TCP-SA option.
The MAC is defined over the following fields in the following order:
1. the TCP pseudoheader: IP source and destination addresses, zero-
padded protocol number and segment length, all in network byte
order, i.e., exactly as used for the TCP checksum [RFC793]:
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+--------+--------+--------+--------+
| Source Address |
+--------+--------+--------+--------+
| Destination Address |
+--------+--------+--------+--------+
| zero | PTCL | TCP Length |
+--------+--------+--------+--------+
Figure 3 TCP pseudoheader [RFC793]
2. TCP header, including options, and where the checksum and TCP-SA
MAC fields are set to zero, all in network byte order
3. TCP data
4. Connection key: a key to be used to in the MAC algorithm, as
required by the particular MAC algorithm used
TCP-SA includes the TCP options because these options are intended to
be end-to-end and some are required for proper TCP operation (e.g.,
SACK, timestamp). Middleboxes may alter TCP options en-route are a
kind of attack and would be successfully detected by TCP-SA.
The TCP-SA option does not indicate the MAC algorithm either
implicitly (as with TCP/MD5) or explicitly (as with some proposed
alternatives) [RFC2385][Bo05][We05]. The particular algorithm used is
considered part of the configuration state of the security
association of the connection and is managed separately (see Section
3).
3. Security Association Management
TCP-SA relies on a TCP Security Association Database (TSAD). TSAD
entries are assumed to be shared at the endpoints where TCP-SA is
used, in advance of the connection:
1. TCP connection identifier (ID), i.e., socket pair - IP source
address, IP destination address, TCP source port, and TCP
destination address [RFC793]. TSAD entries are uniquely determined
by their TCP connection ID.
2. For each of inbound (received TCP segments) and outbound (sent TCP
segments) on this connection:
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a. MAC type for this connection. This includes the MAC algorithm
(e.g., HMAC-MD5, HMAC-SHA1, UMAC, etc.) and the length of the
MAC stored in the option (e.g., 96, 128, etc.). Also, a
setting of NONE must be supported, to indicate that
authentication is not used in this direction; this allows
asymmetric use of TCP-SA. At least one direction
(inbound/outbound) SHOULD have a non-NONE MAC in practice, but
this is not strictly required.
>> When the outbound MAC is set to values other than NONE,
TCP-SA MUST occur in every outbound TCP segment for that
connection; when set to NONE, TCP-SA MUST NOT occur in those
segments.
>> When the inbound MAC is set to values other than NONE, TCP-
SA MUST occur in every inbound TCP segment for that
connection; when set to NONE, TCP-SA MUST NOT occur in those
segments.
b. Connection key. A byte sequence used for connection keying,
this is intended to be a per-connection key, and may be
derived from a separate shared key by an external protocol
over a separate channel.
It is anticipated that TSAD entries for active or opening TCP
connections can be stored in the TCP Control Block (TCB); TSAD
entries for pending connections (in passive or active OPEN) may be
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
connections, the same way that there is only one set of TCBs.
Multiple databases could be used to support virtual hosts, i.e.,
groups of interfaces.
Note that TSAD and the TCP-SA fields omit a key ID; the TCP
connection ID already uniquely specifies the TSAD entry, so a
separate ID is not needed. The TCP-SA fields omit an explicit
algorithm ID; that algorithm is already specified by the TCP
connection ID and stored in the TSAD.
Also note that this document does not address how TSAD entries are
created or destroyed. It is presumed that a TSAD entry affecting
particular connection cannot be destroyed during an active connection
- or, equivalently, that its parameters are copied local to the
connection and so changes would affect only new connections. The TSAD
could be managed by a separate application protocol if desired.
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4. TCP-SA Interaction with TCP
The following is a description of how various TCP states, segments,
events, and interfaces. This description is intended to augment the
description of TCP as provided in RFC793 [RFC793].
4.1. User Interface
The TCP user interface supports active and passive OPEN, SEND,
RECEIVE, CLOSE, STATUS and ABORT.
>> 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
a TSAD entry can be configured.
>> New TSAD entries MUST be checked against a cache of previously
used TSAD entries.
Users are advised to not inappropriately reuse keys [RFC3562].
>> TCP STATUS SHOULD be augmented to allow the TSAD entry of a
current or pending connection to be read (for confirmation).
>> TCP STATUS MUST NOT allow TSAD entries for ongoing TCP connections
(i.e., not in the CLOSED state) to be modified.
TSAD entries for TCP connections not in the CLOSED state are deleted
indirectly using the CLOSE or ABORT commands.
>> Use of CLOSE or ABORT MUST retain the TSAD entry in a cache to
assist with checking for key reuse.
This entry may correspond to one of the wait states of TCP (FINE-
WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, or TIME-WAIT), or
may be stored separately (for connections proceeding rapidly to
CLOSED). The size of this cache 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-SA.
4.2. TCP States and Transitions
TCP includes the states LISTEN, SYN-SENT, SYN-RECEIVED, ESTABLISHED,
FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and
CLOSED.
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>> A TSAD entry MAY be associated with any TCP state.
>> A TSAD entry MAY underspecify the TCP connection for the LISTEN
state. Such an entry MUST NOT be used for more than one connection
progressing out of the LISTEN state.
4.3. TCP Segments
TCP includes control (at least one of SYN, FIN, RST flags set) and
data (none of SYN, FIN, or RST flags set) segments.
>> All TCP segments MUST be checked against the TSAD for matching TCP
connection IDs.
>> TCP segments matching TSAD entries with non-NULL MACs without TCP-
SA, or with TCP-SA and whose MACs do not validate MUST be silently
discarded.
>> TCP segments with TCP-SA but not matching TSAD entries MUST be
silently accepted.
>> 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.
Both warnings, if available, MUST be accessible via the STATUS
interface. Either signal MAY be asynchronous, but if so they MUST be
rate-limited. Either signal MAY be logged; logging SHOULD allow rate-
limiting as well.
All TCP-SA processing occurs between the interface of TCP and IP; for
incoming segments, this occurs after validation of the TCP checksum.
For outgoing segments, this occurs before computation of the TCP
checksum.
Note that the TCP-SA option is not negotiated. It is the
responsibility of the receiver to determine when TCP-SA is required
and to enforce that requirement.
>> Receivers MAY silently accept TCP segments with the TCP-SA option.
4.4. Sending TCP Segments
The following procedure describes the modifications to TCP to support
TCP-SA when a segment departs.
1. Check the segment's TCP connection ID against the TSAD
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2. If there is NO TSAD entry, omit the TCP-SA option. Proceed with
computing the TCP checksum and transmit the segment.
3. If there is a TSAD entry and the outgoing MAC is NONE, omit the
TCP-SA option. Proceed with computing the TCP checksum and
transmit the segment.
4. If there is a TSAD entry and the outgoing MAC is not NONE:
a. Augment the TCP header with the TCP-SA, inserting the
appropriate Length based on the indexed TSAD entry. Update the
TCP header length accordingly.
b. Compute the MAC using the indexed TSAD connection key, MAC,
and data from the segment as specified in Section 2.2.
c. Insert the MAC in the TCP-SA field.
d. Proceed with computing the TCP checksum and transmit the
segment.
4.5. Receiving TCP Segments
The following procedure describes the modifications to TCP to support
TCP-SA when a segment arrives.
1. Check the segments TCP connection ID against the TSAD
2. If there is NO TSAD entry, proceed with TCP processing.
3. If there is a TSAD entry and the incoming MAC is NONE, proceed
with TCP processing.
4. If there is a TSAD entry and the incoming MAC is not NONE:
a. Check that the segment's TCP-SA Length matches the indexed
TSAD Length.
i. If Lengths differ, silently discard the segment. Log
and/or signal the event as indicated in Section 4.3.
b. Compute the segment's MAC using the indexed TSAD MAC algorithm
and connection key, and portions of the segment as indicated
in Section 2.2.
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i. If the computed MAC differs from the TCP-SA MAC field
value, silently discard the segment. Log and/or signal
the event as indicated in Section 4.3.
c. Proceed with TCP processing of the segment.
It is suggested that TCP-SA implementations validate a segment's
Length field before computing a MAC, to reduce the overhead incurred
by spoofed segments with invalid TCP-SA fields.
4.6. Impact on TCP Header Size
The TCP-SA option typically uses a total of 16-18 bytes of TCP header
space. TCP-SA is no larger than and typically 2 bytes smaller than
the TCP/MD5 option. Although TCP option space is limited, we believe
TCP-SA is consistent with the desire to authenticate TCP at the
connection level for similar uses as were intended by TCP/MD5.
5. Key Establishment and Duration Issues
The TCP-SA option does not provide connection key negotiation,
parameter negotiation (MAC algorithm, length, or use of the TCP-SA
option), or rekeying during a connection. We assume out-of-band
mechanisms for key establishment and parameter negotiation.
Deployments desiring more dynamic key and/or parameter management are
encouraged to use the IPsec security suite [RFC4301][RFC4306].
We encourage users of TCP-SA to apply known techniques for generating
appropriate keys, including the use of reasonable connection key
lengths, limited connection key sharing, and limiting the duration of
connection key use [RFC3562].
TCP-SA does not support rekeying as such. Connections needing
rekeying would close the existing connection using the old connection
key and start a new connection using a new connection key.
Applications using TCP-SA will work more efficiently if they support
graceful transition between sequences of such connections, either by
handoff between the two connections while both are open or by
limiting the impact of the first connection closing. Such support is
already being developed for Internet routing protocols, as discussed
in Section 6.
Implementations are encouraged to keep keys in a suitably private
area. Users of TCP-SA are encouraged to use different keys for
inbound and outbound MACs on a given TCP connection.
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6. Use of TCP-SA with Routing Protocols
TCP-SA assumes that applications requiring rekeying are not
significantly affected by TCP connection reestablishment, because
that is the only method for changing keys. Some current routing
protocols, notably BGP, may be affected because they interpret the
stability of TCP connections to indicate the stability of the
communication path to its peers (or of the peers themselves).
This problem has already been addressed in extensions to BGP and BGP
for MPLS, in a mechanism known as "graceful restart" [Re05][Sa04].
Without graceful restart, when a TCP connection is interrupted -
either deliberately (shutdown BGP client) or otherwise (via an
attack) - BGP flushes the routes of that peer from its tables,
causing substantial service interruption, and taking a long time to
reestablish [To06]. In graceful restart, BGP signals its peer in-band
that a connection is to be closed, and the routes are not flushed.
Although TCP/MD5 is used for other routing protocols besides BGP,
notably LDP, PCEP, and MSDP, it is not known whether these protocols
support similar graceful restart or other handoff mechanisms.
Further, the cost of restarting these protocols is nonzero; some
protocols, notably BGP, exchange their entire routing tables upon
restart rather than only their updates. This can result in longer
convergence time and increased bandwidth utilization.
In cases where graceful restart is not feasible or efficient, it may
be necessary to support secure associations with dynamic rekeying. In
those cases, a true key management protocol - such as IKE - is
recommended. Such a mechanism is not included in TCP-AO for
simplicity, notably to avoid complex interactions between key
activity periods and TCP's windowing algorithm.
[can anyone suggest what LDP, PCEP, or MSDP do?]
[is there a citation for BGP restart time/cost?]
7. Interactions with TCP/MD5
TCP-SA is intended to be deployed without regard for existing TCP/MD5
option support.
>> A TCP implementation MUST NOT use both TCP-SA and TCP/MD5 for a
particular TCP connection, but MAY support TCP-SA and TCP/MD5
simultaneously for different connections.
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There is no need to explicitly indicate which of TCP-SA or TCP/MD5 is
used for a particular connection in the TCP segments. Even where the
two used the same hash (e.g., if TCP-SA were to use MD5 rather than
HMAC-MD5) and the same length (128 bits), TCP-SA computes its MAC
over different data (including the TCP-SA option, notably, with the
MAC zeroed) than TCP/MD5. The probability of a TCP-SA segment being
validated by TCP/MD5 or the converse is roughly equivalent to that of
a random party guessing a valid MAC.
8. Security Considerations
Use of TCP-SA, like use of TCP/MD5 or IPsec, will impact host
performance. Connections that are known to use TCP-SA can be attacked
by transmitting segments with invalid MACs. Attackers would need to
know only the TCP connection ID and TCP-SA Length value to
substantially impact the host's processing capacity. This is similar
to the susceptibility of IPsec to on-path attacks, where the IP
addresses and SPI would be visible. For IPsec, the entire SPI space
(32 bits) is arbitrary, whereas for routing protocols typically only
the source port (16 bits) is arbitrary. As a result, it would be
easier for an off-path attacker to spoof a TCP-SA segment that could
cause receiver validation effort. However, we note that between
Internet routers both ports could be arbitrary (i.e., determined a-
priori out of band), which would constitute roughly the same off-path
antispoofing protection of an arbitrary SPI.
TCP-SA, like TCP/MD5, may inhibit connectionless resets. Such resets
typically occur after peer crashes, either in response to new
connection attempts or when data is sent on stale connections; in
either case, the recovering endpoint may lack the connection key
required (e.g., if lost during the crash). This may result in time-
outs, rather than more responsive recovery after such a crash.
TCP-SA does not expose the MAC algorithm used to authenticate a
particular connection; that information is kept in the TSAD at the
endpoints, and is not indicated in the header.
TCP-SA is intended to provide similar protections to IPsec, but is
not intended to replace the use of IPsec or IKE either for more
robust security or more sophisticated security management.
TCP-SA does not address the issue of ICMP attacks on TCP. IPsec makes
recommendations regarding dropping ICMPs in certain contexts, or
requiring that they are endpoint authenticated in others [RFC4301].
There are other mechanisms proposed to reduce the impact of ICMP
attacks by further validating ICMP contents and changing the effect
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of some messages based on TCP state, but these do not provide the
level of authentication for ICMP that TCP-SA provides for TCP [Go06].
>> A TCP-SA implementation MUST allow the system administrator to
configure whether TCP will ignore incoming ICMP messages of Type 3
Codes 2-4 intended for connections that match TSAD entries with non-
NONE inbound MACs. An implementation SHOULD allow ignored ICMPs to be
logged.
This control affects only ICMPs that currently require 'hard errors'
which would abort the TCP connection. This recommendation is intended
to be similar to how IPsec would handle those messages [RFC4301].
9. IANA Considerations
The TCP-SA option reuses the TCP MD5 Signature option (TCP/MD5),
where Kind=19. This document augments that use of this Kind value,
but there is no need to deprecate or override the use of TCP/MD5.
This document suggests that only one key algorithm would be
applicable in either case, and so there would be no confusion for a
given Length and key value as used for authenticating segments of a
given TCP connection.
If this document is approved as an IETF Standard, IANA is requested
to add a registration for TCP-SA to Kind=19, along with the existing
registration for TCP/MD5, and add a pointer to this document.
10. Conclusions
(to be completed)
11. Acknowledgments
This document was inspired by the revisions to TCP/MD5 suggested by
Brian Weis and Ron Bonica [Bo06][We05]. Russ Housley suggested
L4/application layer management of the TSAD.
12. References
12.1. Normative References
[RFC793] Postel, J., "Transmission Control Protocol," STD-007, RFC-
793, [Standard], Sept. 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, [Best Current
Practice], March 1997.
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[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option," RFC-2385 [Proposed Standard], Aug. 1998.
[RFC2403] Madson, C., R. Glenn, "The Use of HMAC-MD5-96 within ESP
and AH," RFC-2403 [Proposed Standard], Nov. 1998.
[RFC4301] Kent, S., K. Seo, "Security Architecture for the Internet
Protocol," RFC-4301, [Proposed Standard], Dec. 2005.
12.2. Informative References
[Be05] Bellovin, S., E. Rescorla, "Deploying a New Hash
Algorithm," presented at the First NIST Cryptographic Hash
Workshop, Oct. 2005.
http://csrc.nist.gov/pki/HashWorkshop/2005/program.htm
[Bu06] Burr, B., "NIST Cryptographic Standards Status Report,"
Invited talk at Internet 2 5th Annual PKI R&D Workshop,
April 2006.
http://middleware.internet2.edu/pki06/proceedings/
[Bo06] Bonica, R., "Authentication for TCP-based Routing and
Management Protocols," draft-bonica-tcp-auth-04, (work in
progress), Jan. 2006.
[Go06] Gont, F., "ICMP attacks against TCP," draft-ietf-tcpm-icmp-
attacks-00, Feb. 2006.
[Re05] Rekhter, Y., R. Aggarwal, "Graceful Restart Mechanism for
BGP with MPLS," draft-ietf-mpls-bgp-mpls-restart-05, (work
in progress), Aug. 2005.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC-1321,
April 1992.
[RFC3562] Leech, M., "Key Management Considerations for the TCP MD5
Signature Option," RFC-3562, July 2003.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol," RFC-
4306, [Proposed Standard], Dec. 2005.
[Sa04] Sangli, S., Y. Rekhter, R. Fernando, J. Scudder, E. Chen,
"Graceful Restart Mechanism for BGP," draft-ietf-idr-
restart-10 (work in progress), June 2004.
[To06] Touch, J., "Defending TCP Against Spoofing Attacks," draft-
ietf-tcpm-tcp-antispoof-04, May 2006.
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[We05] Weis, B., "TCP Message Authentication Code Option," draft-
weis-tcp-mac-option-00 (work in progress), Dec. 2005.
[We06] Weis, B., "Automated key selection extension for the TCP
Authentication Option," draft-weis-tcp-auth-auto-ks-00
(work in progress), Feb. 2006.
Author's Addresses
Joe Touch
USC/ISI
4676 Admiralty Way
Marina del Rey, CA 90292-6695
U.S.A.
Phone: +1 (310) 448-9151
Email: touch@isi.edu
URL: http://www.isi.edu/touch
Allison Mankin
Washington, DC
U.S.A.
Phone: 1 301 728 7199
Email: mankin@psg.com
URL: http://www.psg.com/~mankin/
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