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Versions: 00 01 02 03 04 05 06 07 RFC 6039

Internet-Draft      Routing Protocol Protection Issues      October 2008


   Network Working Group                                 Vishwas Manral
   Internet-Draft                                           IP Infusion
   Expires: March 2009                                       Russ White
   Intended Status: Informational                         Cisco Systems
                                                           Manav Bhatia
                                                         Alcatel-Lucent

     Issues with existing Cryptographic Protection Methods for Routing
                                 Protocols

          draft-ietf-opsec-routing-protocols-crypto-issues-00.txt

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Abstract

   Routing protocols are designed to use cryptographic mechanisms to
   authenticate data being received from a neighboring router to ensure
   that it has not been modified in transit, and actually originated
   from the neighboring router purporting to have originating the data.
   Most of the cryptographic mechanisms defined to date rely on hash
   algorithms applied to the data in the routing protocol packet, which
   means the data is transported, in the clear, along with a signature
   based on the data itself.  These mechanisms rely on the manual
   configuration of the keys used to seed, or build, these hash based
   signatures.  This document outlines some of the problems with manual
   keying of these cryptographic algorithms.

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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. Problem Statement..............................................2
   2. Open Shortest Path First (OSPFv2)..............................4
      2.1 Management Issues with OSPF................................4
      2.2 Technical Issues with OSPF.................................4
   3. Open Shortest Path First (OSPFv3)..............................5
      3.1 Management Issues with OSPFv3..............................6
      3.2 Technical Issues with OSPFv3...............................6
   4. Intermediate System to Intermediate System Routing Protocol (IS-
   IS)...............................................................7
      4.1 Management Issues with IS-IS...............................7
      4.2 Technical Issues with IS-IS................................8
   5. Border Gateway Protocol (BGP-4)................................9
      5.1 Management Issues with BGP-4..............................10
      5.2 Technical Issues with BGP-4...............................10
   6. The Routing Information Protocol (RIP)........................10
   7. Security Considerations.......................................12
   8. Acknowledgements..............................................12
   9. IANA Considerations...........................................12
   10. References...................................................12
      10.1 Normative References.....................................12
      10.2 Informative References...................................13
   11. Contributor's Address........................................14
   12. Author's Addresses...........................................14


1. Problem Statement

   Routing protocols, such as OSPF [RFC2328] [RFC5340], IS-IS [RFC1195],
   and BGP-4 [RFC4271], rely on various mechanisms to create a
   cryptographic digest of each transmitted routing protocol.
   Traditionally, these digests are the results of a hash algorithm,
   such as MD5 [RFC1321], across the contents of the packet being
   transmitted, using a secret key as the hash base (or seed).  These
   digests are recomputed by the receiving router, using the same key as
   the originating router used to create the hash, and compared with the
   transmitted digest to verify:

   o  That the router originating this piece of data is authorized to
      peer with the local router, and to transmit routing data.  This
      generally protects against falsely generated routing data being
      injected into a routing system by rogue systems.

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   o  That the data has not been changed while transiting between the
      two neighboring routers.

   These sorts of authentication methods are not generally used to
   protect the confidentiality of information being exchanged between
   routers, since this information (entries in the routing table) is
   generally freely available in many other context; if anyone has
   access to the physical media between two routers exchanging routing
   data, they will also probably have other ways to capture or otherwise
   discover the contents of the routing tables in those routers.

   The main problems with the authentication mechanisms defined today
   revolve around:

   o  Manual configuration of shared secret keys, especially in large
      scale networks, poses a major management problem, especially as
      there is generally no way to gracefully move from one secret key
      to another.

   o  In some cases, when manual keys are configured, some forms of
      replay protection are disabled, allowing the routing protocol to
      be attacked.

   In fact, the MD5 digest algorithm was not designed to be used in the
   way most routing protocols are using it, which can lead to serious
   security implications in the future.

   A preimage attack would enable someone to find an input message that
   causes a hash function to produce a particular output. In contrast, a
   collision attack finds two messages with the same hash, but the
   attacker can't pick what the hash will be. Feasible collision attacks
   against MD4, MD5, HAVAL-128, and RIPEMD were found by the Chinese
   researcher Xiaoyun Wang with co-authors Dengguo Feng, Xuejia Lai, and
   Hongbo Yu.

   The collision vulnerability does not introduce any obvious or known
   attacks on routing protocols. However pre-image attacks could cause
   problems.

   Protocols themselves have some built-in protection against collision
   attacks. A lot of values for a lot of fields in the protocol are
   invalid. For example, for OSPF the LSA type can be from 1 to 11. Any
   other value in the field will result in the packet being dropped.

   Assume two packets M and M' are generated which have the same hash.
   The above condition will further reduce the probability of the two
   messages also being correct messages from the protocol perspective,
   as a lot of values are themselves not valid.



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2. Open Shortest Path First (OSPFv2)

   OSPF [RFC2328] describes the use of an MD5 digest with OSPF packets.
   MD5 keys are manually configured. The OSPF packet Header includes an
   authentication type field as well as 64 bits of data for use by the
   appropriate authentication scheme. OSPF also provides for a non-
   decreasing sequence number to be included in each OSPF protocol
   packet to protect against replay attacks.

2.1 Management Issues with OSPF

   According to the OSPF specification [RFC2328], digests are applied
   to packets transmitted between adjacent neighbors, rather than being
   applied to the routing information originated by a router (digests
   are not applied at the LSA level, but rather at the packet level).
   [RFC2328] states that any set of OSPF routers adjacent across a
   single link may use a different key to build MD5 digests than the key
   used to build MD5 digests on any other link.  Thus, MD5 keys may be
   configured, and changed, on a per-link basis in an OSPF network.

   OSPF does not specify a mechanisms to negotiate keys, nor does it
   specify any mechanism to negotiate the hash algorithms to be used.

   With the proliferation of the number of hash algorithms, as well as
   the need to continuously upgrade the algorithms, manually configuring
   the information becomes very tedious.

2.2 Technical Issues with OSPF

   While OSPF provides relatively strong protection through the
   inclusion of MD5 signatures, with additional data and sequence
   numbers in transmitted packets, there are still two possible attacks
   against OSPF:

   o  The sequence number is initialized to zero when forming an
      adjacency with a newly discovered neighbor, and is also set to
      zero whenever the neighbor is brought down.  If the
      cryptographically protected packets of a router that is brought
      down (for administrative or other reasons) are stored by a
      malicious router, the new router could replay the packets from
      the previous session, thus forcing traffic through the malicious
      router.  Dropping of such packets by the router could result in
      blackholes.  Also forwarding wrong packets could result in
      routing loops.

   o  OSPF allows multiple packets with the same sequence number.
      This could mean the same packet can be replayed many times before
      the next legitimate packet is sent.  An attacker may resend the
      same packet repeatedly until the next hello packet is transmitted
      and received, which means the hello interval determines the attack
      window.
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   o  OSPF does not specify the use of any particular hash algorithm,
      however the use of only MD5 is specified in the document. Most
      OSPF implementations only support MD5.

      Recently, attacks on the collision-resistance property of the MD5
      and SHA-1 hash functions have been discovered; [RFC4270]
      summarizes the discoveries. The attacks on MD5 are practical on
      any modern computer. For this reason the use of these algorithms
      needs to be discouraged.

   o  OSPF on a broadcast network shares the same key between all
      neighbors on a that network. Some OSPF packets are sent to a
      multicast address.

      This allows spoofing by any malicious neighbor very easy.
      Possession of the key itself is used as an identity check. There
      is no other identity check used. A neighbor could send a packet
      specifying the packet came from some other neighbor and there
      would be no way in which the attacked router could figure out the
      identity of the packet sender.

   o  OSPF neighbors on broadcast, NBMA and point-to-multipoint
      networks are identified by the IP address in the IP header.
      Because the IP header is not covered by the MAC in the
      cryptographic authentication scheme as described in RFC 2328, an
      attack can be made exploiting this vulnerability.

      Assume the following scenario.

      R1 sends an authenticated HELLO to R2. This HELLO is captured
      and replayed back to R1, changing the source IP in the IP header
      to that of R2.

      R1 not finding itself in HELLO would deduce that the connection is
      not bidirectional and would bring down the adjacency.

3. Open Shortest Path First (OSPFv3)

   OSPFv3 [RFC5340] relies on the IP Authentication Header described in
   [RFC4302] and the IP Encapsulating Payload described in [RFC4303] to
   cryptographically sign routing information passed between routers.
   When using ESP, the null encryption algorithm [RFC2410] is used, so
   the data carried in the OSPFv3 packets is signed, but not encrypted.
   This provides data origin authentication for adjacent routers, and
   data integrity which gives the assurance data transmitted by a router
   has not changed in transit.


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   However it does not provide confidentiality of the information
   transmitted. [RFC4552] mandates the use of ESP with null encryption
   for authentication and also does encourage the use of confidentiality
   to protect the privacy of the routing information transmitted, using
   ESP encryption.

   [RFC4552] describes OSPFv3's use of AH and ESP, and specifies
   that only manual keying of routing information may be used.

3.1 Management Issues with OSPFv3

   The OSPFv3 security document [RFC4552] discusses, at length, the
   reasoning behind using manually configured keys, rather than some
   automated key management protocol such as IKEv2 [RFC4306]. The
   primary problem is that all current key management mechanisms are
   designed for a one-to-one correlation of keys, while OSPF adjacencies
   are formed on a one-to-many basis.  This forces the system
   administrator to use manually configured SAs and cryptographic keys
   to provide the authentication and, if desired, confidentiality
   services.

   [RFC4552] states that

      As it is not possible as per the current standards to provide
      complete replay protection while using manual keying, the proposed
      solution will not provide protection against replay attacks.

   The primary administrative issue with manually configured SA's and
   keys in the OSPFv3 case is the simple management issue of maintaining
   matching sets of keys on all routers within a network.  [RFC4552]
   does not require that all OSPFv3 routers have the same key configured
   for every neighbor, so each set of neighbors connected to a single
   link could have a different key configured.  While this makes it
   easier to change the keys, by forcing the system administrator to
   only change the keys on the routers on a  single link, the process of
   manual configuration for all the routers in a network to change the
   keys used for OSPFv3 digests and confidentiality on a periodic basis
   can be difficult.

3.2 Technical Issues with OSPFv3

   The primary technical concern with the current specifications for
   OSPFv3 is that when manual SA and key management is used as [RFC4302]
   specifies, in section 3.3.2, Sequence Number Generation: "The sender
   assumes anti-replay is enabled as a default, unless otherwise
   notified by the receiver (see 3.4.3) or if the SA was configured
   using manual key management." Replayed OSPFv3 packets can cause
   several failures in a network, including:

   o  Replaying hello packets with an empty neighbor list can cause all
      the neighbor adjacencies with the sending router to be reset,
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      disrupting network communications.

   o  Replaying hello packets from early in the designated router
      election process on broadcast links can cause all the neighbor
      adjacencies with the sending router to be reset, disrupting
      network communications.

   o  Replaying database description (DB-Description) packets can cause
      all FULL neighbor adjacencies with the sending router to be reset,
      disrupting network communications.

   o  Replaying link state request (LS-Request) packets can cause all
      FULL neighbor adjacencies with the sending router to be reset,
      disrupting network communications.

   o  Capturing a full adjacency process (from two-way all the way to
      FULL state), and then replaying this process when the router is no
      longer attached can cause a false adjacency to be formed, allowing
      an attacker to attract and black hole traffic.

   o  OSPFv3 on a broadcast network shares the same key between all
      neighbors on that network. Some OSPF packets are sent to a
      multicast address.

      This allows spoofing by any malicious neighbor very easy.
      Possession of the key itself is used as an identity check. There
      is no other identity check used. A neighbor could send a packet
      specifying the packet came from some other neighbor and there
      would be no way in which the attacked router could figure out the
      identity of the packet sender.

4. Intermediate System to Intermediate System Routing Protocol (IS-IS)

   Integrated  IS-IS [RFC1195] uses HMAC-MD5 authentication with manual
   keying, as described in [RFC5304]. There is no provision within IS-IS
   to encrypt the body of a routing protocol message.

4.1 Management Issues with IS-IS

   [RFC5304] states that each LSP generated by an intermediate system is
   signed with the HMAC-MD5 algorithm using a key manually defined by
   the network administrator.  Since authentication is performed on the
   LSPs transmitted by an intermediate system, rather than on the
   packets transmitted to a specific neighbor, it is implied that all
   the intermediate systems within a single flooding domain must be
   configured with the same key for authentication to work correctly.
   The initial configuration of manual keys for authentication within an
   IS-IS network is simplified by a state where LSPs containing HMAC-MD5
   authentication TLVs are accepted, but the digest is not validated.
   Once an initial set of keys is configured on all routers, however,
   changing those keys becomes much more difficult.
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   IS-IS [RFC1195] does not specify a mechanism to negotiate keys, nor
   does it specify any mechanism to negotiate the hash algorithms to be
   used.

   With the proliferation of the number of hash algorithms, as well as

   the need to continuously upgrade the algorithms, manually configuring
   the information becomes very tedious.

4.2 Technical Issues with IS-IS

   [RFC5304] states: "This mechanism does not prevent replay attacks,
   however, in most cases, such attacks would trigger existing
   mechanisms in the IS-IS protocol that would effectively reject old
   information."  The few cases where existing mechanisms in the IS-IS
   protocol would not effectively reject old information is the case of
   hello packets (IIHs) used to discover neighbors, and SNP packets.

   As described in IS-IS [RFC1195], a list of known neighbors is
   included in each hello transmitted by an intermediate system, to
   ensure two-way communications with any specific neighbor before
   exchanging link state databases.

   IS-IS does not provide a sequence number. Hence IS-IS packets are
   liable to replay attacks; any packet can be replayed at any point
   of time, as long as the keys used are the same.

   A hello packet containing a digest within a TLV, and an empty
   neighbor list, could be replayed, causing all adjacencies with the
   original transmitting intermediate system to be restarted.

   A replay of an old CSNP packets could cause LSPs to be flooded, thus
   causing an LSP storm.

   IS-IS specifies the use of the hash algorithm HMAC-MD5 to protect
   IS-IS PDUs.

   IS-IS does not have a notion of Key ID. During Key rollover, each
   message received has to be checked for integrity against all keys
   that are valid. A DoS attack may be caused by sending IS-IS packets
   with random hashes. This will cause the IS-IS packet to be checked
   for authentication with all possible keys, thus increasing the amount
   of processing required.

   Recently, attacks on the collision-resistance property of the MD5 and
   SHA-1 hash functions have been discovered; [RFC4270] summarizes the
   discoveries. The attacks on MD5 are practical on any modern computer.
   For this reason, the use of these algorithms needs to be discouraged.

   HMACs are not susceptible to any known collision-reduction attack.
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   However, IS-IS should provide a way to upgrade to other stronger
   algorithms.

   IS-IS on a broadcast network shares the same key between all
   neighbors on that network.

   This makes spoofing by any malicious neighbor very easy since IS-IS
   PDUs are sent to a link layer multicast address. Possession of the
   key itself is used as an identity check and no other identity check
   is performed. A neighbor could send a packet specifying the packet
   came from some other neighbor and there would be no way in which the
   attacked router could figure out the identity of the packet sender.

   As the lifetime is not covered in the authentication, an IS-IS router
   can receive its own self generated LSP segment with zero lifetime
   remaining. In that case, if it has a copy with non-zero lifetime, it
   purges that LSP i.e., it increments the current sequence number and
   floods all the segments again. This is much worse in IS-IS, as there
   exists only one LSP other than the pseudonode LSPs for the LANs on
   which it is the Designated Intermediate System (DIS).

   This way an attack can force the router to flood all segments, which
   can be quite a lot if the number of routes is large. It also causes
   the sequence number of all the LSPs to increase fast. If the sequence
   number increases to the maximum (0xFFFFFFFF), the IS-IS process must
   shut down for around 20+ minutes (MaxAge + ZeroAgeLifetime) to allow
   the old LSPs to age out of all the router databases.

5. Border Gateway Protocol (BGP-4)

   BGP-4 [RFC4271] uses TCP [RFC0793] for transporting routing
   information between BGP speakers which have formed an adjacency.

   [RFC2385] describes the use of TCP MD5 signature option for providing
   data origin authentication and data integrity protection of these BGP
   packets, and [RFC3562] gives suggestions for choosing the key length
   for the ad-hoc keyed-MD5 mechanism specified in [RFC2385]. There is
   no provision for confidentiality for any of these BGP messages.

   This problem is made worse by the nature of the environment where BGP
   is typically used, between autonomous networks (under different
   administrative control). While routers running interior gateway
   protocols may all be configured using the same keys, and have their
   key rollover policies coordinated or set by the same administrative
   authority, two BGP peering BGP speakers may be in different
   administrative domains, with different policies for key strength,
   rollover times, etc. An autonomous system must often support a large
   number of keys on different BGP borders, since each connecting AS
   represents a different administrative entity.


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5.1 Management Issues with BGP-4

   Each pair of BGP speakers forming an adjacency may have a different
   MD5 shared key, facilitating the configuration and changing of keys
   across a large scale network.  Manual configuration and maintenance
   of cryptographic keys on all routers is a challenge in any large
   scale environment, however.  Most BGP implementations will accept BGP
   packets with a bad digest for the hold interval negotiated between
   BGP peers at peering startup, allowing MD5 keys to be changed without
   impacting the operation of the network.  This technique does,
   however, allow some short period of time, during which an attacker
   may inject BGP packets with false MD5 digests into the network and
   can expect those packets to be accepted, even though their MD5
   digests are not valid.

5.2 Technical Issues with BGP-4

   Since BGP relies on TCP [RFC0793] for transporting data between BGP
   speakers, BGP can rely on TCP's protections against data corruption
   and replay to prevent replay attacks against BGP sessions.  A great
   deal of research has gone into the difficulty or ease with which an
   attacker can overcome these protections, including [TCP-WINDOW] and
   [BGP-ATTACK].  Most implementations of BGP have modified their TCP
   implementations to resolve the security vulnerabilities described in
   these references, where possible.

   However, as mentioned earlier, MD5 is vulnerable to collision
   attacks, and can be attacked through several means, such as those
   explored in [MD5-ATTACK].

   Though it can be argued that the collision attacks do not have a
   practical implication in this scenario, the use of MD5 is
   discouraged.

   Routers performing cryptographic processing of packets in software
   may be easier to attack. An attacker may be able to transmit enough
   traffic with false digests to a router that the router's processor
   and memory resources are consumed, causing the router to be unable to
   perform normal processing. This is particularly problematic at
   connections to devices not under local administrative control.

6. The Routing Information Protocol (RIP)

   The initial version of RIP was specified in STD34 [RFC1058]. This
   version did not provide for any authentication or authorization of
   routing data, and thus was vulnerable to any of the various attacks
   against routing protocols. This was one of the reasons why this
   protocol has been moved to Historic status long ago [RFC1923].



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   RIPv2, originally specified in [RFC1388], then [RFC1723], has been
   finalized in STD56 [RFC2453]. This version of the protocol provides
   for authenticating packets by carrying a digest. The details thereof
   have initially been provided in "RIP-2 MD5 Authentication" [RFC2082];
   "RIPv2 Cryptographic Authentication" [RFC4822] obsoletes [RFC2082]
   and adds details of how the SHA family of hash algorithms can be used
   to protext RIPv2, whereas [RFC2082] only specified the use of Keyed
   MD5.

   o  The sequence number is initialized to zero, at the beginning of
      time, and is also set to zero whenever the neighbor is brought
      down. If the cryptographically protected packets of a router that
      is brought down (for administrative or other reasons) are stored
      by a malicious router, the new router could replay the packets
      from the previous session thus forcing traffic through the
      malicious router.  Dropping of such packets by the router could
      result in blackholes.  Also forwarding wrong packets could
      result in routing loops.

   o  RIPv2 allows multiple packets with the same sequence number.
      This could mean the same packet can be replayed many times before
      the next legitimate packet is sent.  An attacker may resend the
      same packet repeatedly until the next hello packet is transmitted
      and received, which means the hello interval determines the attack
      window.

   o  RIPv2 does not specify the use of any particular hash algorithm.
      Currently, RIP implementations only support keyed MD5 [RFC2082].
      MD5 is vulnerable to attacks [MD5-ATTACK].

   o  RIPv2 Cryptographic Authentication [RFC4822] does not cover the
      UDP and the IP headers. It is thus possible for an attacker to
      modify the fields in the above headers without any of the routers
      getting to know about it.

      There isn't much that can be done by modifying the UDP header as
      RIP only uses it to compute the length of the RIP packet. Any
      changes introduced in the UDP header would fail the RIP
      authentication, and this attack will thus, not work.

      However, RIP uses the source IP address from the IP header to
      determine the RIP neighbor from which it has learnt the RIP
      Updates.  This can be used by an attacker to disrupt the RIP
      routing sessions between two routers R1 and R2, as shown in the
      following examples:

      Scenario 1:

      R1 sends an authenticated RIP message to R2 with a cryptographic
      sequence num X.

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      The attacker merely needs get hold of a higher sequence number
      packet from the LAN. It could also be a packet originated by R2
      either from this session, or from some earlier session.

      The attacker can then replay this packet to R2 by changing the
      source IP to that of R1.

      R2 would now no longer accept any more RIP Updates from R1 as

      those would have a lower cryptographic sequence number. After 180
      secs (or less), R2 would time out R1 and bring down the RIP
      session.

      Scenario 2:

      R1 announces a route with cost C1 to R2. This packet can be
      captured by an attacker. Later, if this cost changes and R1
      announces this with some other cost C2, the attacker can replay
      the captured packet by modifying the source IP to some new
      arbitrary IP address. It can this way masquerade as some other
      router.

      R2 will accept this route and the router as a new gateway, and
      would use the non existent router as a next hop for that network.
      This would obviously only work if C1 < C2.

7. Security Considerations

   This draft outlines security issues arising from the manual keying of
   cryptographic keys for various routing protocols.  No changes to any
   protocols are proposed in this draft, and no new security
   requirements result.

8. Acknowledgements

   We would like to acknowledge Sam Hartman, Ran Atkinson, Steve Kent
   and Brian Weis for their initial comments on this draft.  Thanks to
   Merike Kaeo and Alfred Hoenes for reviewing many sections of the
   draft and providing lot of useful comments.

9. IANA Considerations

   This document places no requests to IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

10. References

10.1 Normative References


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   [RFC0793]   Postel, J., "Transmission Control Protocol", STD 7,
               RFC 793, September 1981.

   [RFC1195]   Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
               dual environments", RFC 1195, December 1990.

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2328]   Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC2385]   Heffernan, A., "Protection of BGP Sessions via the TCP
               MD5 Signature Option", RFC 2385, August 1998.

   [RFC2453]   Malkin, G., "RIP Version 2", RFC 2453, November 1998

   [RFC5340]   Coltun, R., Ferguson, D., Moy, J., and Lindem, A., "OSPF
               for IPv6", RFC 5340, July 2008.

   [RFC5304]   Li, T. and Atkinson, R., "Intermediate System to
               Intermediate System (IS-IS) Cryptographic
               Authentication", RFC 5304, October 2008.

   [RFC4271]   Rekhter , Y., Li, T., and S. Hares, "A Border Gateway
               Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4302]   Kent, S., "IP Authentication Header",
               RFC 4302, December 2005.

   [RFC4303]   Kent, S., "IP Encapsulating Security Payload (ESP)",
               RFC 4303, December 2005.

   [RFC4552]   Gupta, M. and N. Melam, "Authentication/Confidentiality
               for OSPFv3", RFC 4552, January 2006

   [RFC4822]   R. Atkinson and M. Fanto, "RIPv2 Cryptographic
               Authentication", RFC 4822, February 2007

10.2 Informative References

   [RFC1058]   Hedrick, C., "Routing Information Protocol", RFC 1058,
               June 1988.

   [RFC1321]   Rivest, R., "The MD5 Message-Digest Algorithm", RFC
               1321, April 1992

   [RFC1388]   Malkin, G., "RIP Version 2 Carrying Additional
               Information", RFC 1388, January 1993.



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   [RFC1723]   Malkin, G., "RIP Version 2 - Carrying Additional
               Information", STD 56, RFC 1723, November 1994.
   [RFC1923]   Halpern, J. and Bradner, S., "RIPv1 Applicability
               Statement for Historic Status", RFC 1923, March 1996

   [RFC2082]   Baker, F. and Atkinson, R., "RIP-2 MD5
               Authentication", RFC 2082, January 1997

   [RFC2410]   Kent, S. and Glenn, R., "The NULL Encryption Algorithm
               and Its Use With IPsec", RFC 2410, November 1998

   [RFC3562]   Leech, M., "Key Management Considerations for the TCP
               MD5 Signature Option", RFC 3562, July 2003.

   [RFC4270]   Hoffman, P. and B. Schneier, "Attacks on Cryptographic
               Hashes in Internet Protocols", RFC 4270, November 2005.

   [RFC4306]   Kaufman, C., "The Internet Key Exchange (IKEv2)
               Protocol", RFC 4306, December 2005

   [BGP-ATTACK]  Convery, S. and M. Franz, "BGP Vulnerability Testing:
                 Separating Fact from FUD v1.00", June 2003.

   [TCP-WINDOW]  Watson, T., "TCP Reset Spoofing", October 2003.

   [MD5-ATTACK]   Wang, X. et al., "Collisions for Hash Functions MD4,
                  MD5, HAVAL-128 and RIPEMD", August 2004,
                  http://eprint.iacr.org/2004/199

11. Contributor's Address

   Sue Hares
   NextHop
   USA
   Email: shares@nexthop.com

12. Author's Addresses

   Manav Bhatia
   Alcatel-Lucent
   Bangalore, India
   Email: manav@alcatel-lucent.com

   Vishwas Manral
   IP Infusion
   Almora, Uttarakhand
   India
   Email: vishwas@ipinfusion.com

   Russ White
   Cisco Systems
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Internet-Draft      Routing Protocol Protection Issues      October 2008


   RTP North Carolina
   USA
   Email: riw@cisco.com

Full Copyright Statement

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