Internet Draft                                           September 2010


   Network Working Group                                   Manav Bhatia
   Internet Draft                                        Alcatel-Lucent
   Expires: March 28, 2011                               Vishwas Manral
   Intended Status: Informational                           IP Infusion
                                                     September 27, 2010

           Cryptographic Authentication Algorithm Implementation
                    Requirements for Routing Protocols

              draft-ietf-opsec-igp-crypto-requirements-01.txt

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Abstract

   The routing protocols Open Shortest Path First version 2 (OSPFv2),
   Intermediate System to Intermediate System (IS-IS) and Routing
   Information Protocol (RIP) currently define Clear Text and MD5
   (Message Digest 5) methods for authenticating protocol packets.
   Recently effort has been made to add support for the SHA (Secure Hash
   Algorithm) family of hash functions for the purpose of authenticating
   routing protocol packets for RIP, IS-IS and OSPF.

   To encourage interoperability between disparate implementations, it
   is imperative that we specify the expected minimal set of algorithms
   thereby ensuring that there is at least one algorithm that all
   implementations will have in common.

   This document examines the current set of available algorithms with
   interoperability and effective cryptographic authentication
   protection being the principle considerations. Cryptographic
   authentication of these routing protocols requires the availability
   of the same algorithms in disparate implementations. It is desirable
   that newly specified algorithms should be implemented and available
   in routing protocol implementations because they may be promoted to
   requirements at some future time.

Table of Contents

   1. Introduction...................................................3
   2. Intermediate System to Intermediate System (IS-IS).............4
      2.1 Authentication Scheme Selection............................4
      2.2 Authentication Algorithm Selection.........................5
   3. Open Shortest Path First Version 2(OSPFv2).....................5
      3.1 Authentication Scheme Selection............................5
      3.2 Authentication Algorithm Selection.........................6
   4. Open Shortest Path First Version 3 (OSPFv3)....................6
   5. Routing Information Protocol Version 2 (RIPv2).................6
      5.1 Authentication Scheme Selection............................7
      5.2 Authentication Algorithm Selection.........................7
   6. Routing Information Protocol for IPv6 (RIPng)..................8
   7. Security Considerations........................................8
   8. Acknowledgements...............................................9
   9. IANA Considerations............................................9
   10. References....................................................9
      10.1 Normative References......................................9
      10.2 Informative References...................................10
   Author's Addresses...............................................10





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. Introduction

   Most routing protocols include three different types of
   authentication schemes: Null authentication, Clear Text Password and
   a Cryptographic Authentication scheme. Null authentication is
   equivalent to having no authentication scheme at all.

   In a clear text scheme, also known as, simple password scheme, the
   password is exchanged in the clear on the network and anyone with
   physical access to the network can learn the password and compromise
   the integrity of the routing domain. While the Password scheme
   protects from accidental establishment of routing session in a given
   domain, it offers little additional protection.

   In a cryptographic authentication scheme, routers share a secret key
   which is used to generate a message authentication code for each of
   the protocol packets.  Today, message authentication codes often use
   a keyed MD5 digest.  The recent escalating series of attacks on MD5
   raise concerns about its remaining useful lifetime. These attacks may
   not necessarily result in direct vulnerabilities for keyed MD5
   digests as message authentication codes because the colliding message
   may not correspond to a syntactically correct protocol packet.  There
   is a however a need felt to deprecate MD5 [RFC1321] in favor of
   stronger message authentication code algorithms.

   In light of these considerations there have been proposals for adding
   support of the SHA [SHS] family of hash algorithms for authenticating
   routing protocol packets in RIP [RFC2453], IS-IS [ISO] [RFC1195] and
   OSPF [RFC2328].

   However, the nature of cryptography is that algorithmic
   improvement is an ongoing process and as is the exploration and
   refinement of attack vectors. An algorithm believed to be strong
   today may be demonstrated to be weak tomorrow. Given this, the choice
   of preferred algorithm should favor the minimization of the
   likelihood of it being compromised quickly.

   It should be recognized that preferred algorithm(s) will change over
   time to adapt to the evolving threats. The selection of preferred
   algorithms may well not be reflected in the base protocol
   specification. As protocols are extended the preference for presently
   stronger algorithms presents a problem both on the question of
   interoperability of existing and future implementations with respect
   to standards and operational preference for the configuration as
   deployed. This document intends to provide guidance to implementers
   in anticipation of operational preference.





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   It is expected an implementation should support changing of Security
   (Authentication) Keys. Changing Keys periodically is a good security
   practice.

   Implementations can support in-service key change so that no control
   packets are lost. During such Key change more than one key can be
   active for receiving packets for a session. Some protocols support
   Key ID which allows the two ends of a session to have multiple keys
   simultaneously for a session. Key change however is managed outside
   the scope of the protocols themselves and can be done manually via
   operator intervention, or dynamically based on some timer or a
   security protocol.

. Intermediate System to Intermediate System (IS-IS)

   The IS-IS specification allows for authentication of its Protocol
   Data Units (PDUs) via the authentication TLV (TLV 10) in the PDU. The
   base specification had provisions only for clear text passwords. RFC
   5304 [RFC5304] extends the authentication capabilities by providing
   HMAC-MD5 authentication for IS-IS PDUs.

   RFC 5310 [RFC5310] adds support for the use of the SHA family of hash
   algorithms for authenticating IS-IS PDUs.

2.1 Authentication Scheme Selection

   In order for IS-IS implementations to interoperate with the use of
   security, they must support one or more authentication schemes in
   common. This section specifies the preference for standards
   conformant IS-IS implementations, which desire to utilize the
   security feature.

   The earliest interoperability requirement for authentication as
   stated by [ISO] [RFC1195] required all implementations to support
   Clear Text Password.  This authentication scheme's utility is limited
   to precluding the accidental introduction of a new IS into a
   broadcast domain. We believe that operators should not use this
   scheme as it provides no protection against an attacker with access
   to the broadcast domain as anyone can determine the secret password
   through inspection of the PDU. This mechanism does not provide any
   significant level of security and should be avoided.

   [RFC5304] mandates the use of HMAC-MD5 for cryptographically
   authenticating the IS-IS PDUs. It is likely that this may get
   deprecated in favor of the generic cryptographic authentication
   scheme defined in [RFC5310] in the future deployments, so new
   implementations should support this scheme.




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2.2
Authentication Algorithm Selection

   For IS-IS implementations to interoperate, they must have support for
   one or more authentication algorithms in common.

   This section details the authentication algorithm requirements for
   standards conformant IS-IS implementations.

   [RFC5304] mandates the use of HMAC-MD5 for cryptographically
   authenticating the IS-IS PDUs. It is likely that this may get
   deprecated in favor of HMAC-SHA-1 as defined in [RFC5310] in the
   future deployments, so new implementations should support this
   algorithm.

   Implementations may start providing support for HMAC-SHA-256/HMAC-
   SHA-384/HMAC-SHA-512 as these algorithms may be necessary in the
   future.

3.
Open Shortest Path First Version 2(OSPFv2)

   OSPFv2 as defined in [RFC2328] includes three different types of
   authentication schemes: Null authentication, simple password and
   cryptographic authentication. Null authentication is semantically
   equivalent to no authentication. In the simple password scheme of
   authentication, the passwords are exchanged in the clear on the
   network. Anyone with physical access to the network can learn the
   password and compromise the security of the OSPFv2 domain.

   In the cryptographic authentication scheme, the OSPFv2 routers on a
   common network/subnet are configured with a shared secret which is
   used to generate a keyed MD5 digest for each packet. A monotonically
   increasing sequence number scheme is used to protect against replay
   attacks.

   RFC 5709 [RFC5709] adds support for the use of the SHA family of hash
   algorithms for authentication of OSPFv2 packets.


3.1 Authentication Scheme Selection

   For OSPF implementations to interoperate with the use of security,
   they must have one or more authentication schemes in common. This
   section specifies the preference for standards conformant OSPFv2
   implementations, which desire to utilize the security feature.

   While [RFC2328] mandates the use of NULL Authentication, its use is
   deprecated in any context where the operator wishes to authenticate
   the OSPFv2 packets in their network.



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   Similarly Simple Password, also mandatory per [RFC2328], should be
   used when the operator only wants to preclude the accidental
   introduction of a router into the domain. This scheme is not useful
   when the operator wants to authenticate the OSPFv2 packets.

   Cryptographic Authentication is a mandatory scheme as defined in
   [RFC2328] and all conformant implementations must support this.

3.2
Authentication Algorithm Selection

   For OSPFv2 implementations to interoperate, they must support one or
   more cryptographic authentication algorithms in common.

   [RFC2328] states that implementations must offer keyed MD5
   authentication. It is likely that this will be deprecated in favor of
   HMAC-SHA-1 and HMAC-SHA-256 [RFC5709] in future deployments, so new
   implementations should support these algorithms.

   Operators should consider migration to HMAC-SHA-256 if they desire a
   stronger cryptographic algorithm for authentication of OSPFv2
   packets.

   Implementations may start providing support for HMAC-SHA-1/HMAC-SHA-
   384/HMAC-SHA-512 [RFC5709] as these algorithms may be preferred in
   the future.

4.
Open Shortest Path First Version 3 (OSPFv3)

   OSPFv3 [RFC5340] relies on the IPv6 Authentication Header (AH)
   [RFC4302] and IPv6 Encapsulating Security Payload (ESP) [RFC4303] in
   order to provide integrity, authentication, and/or confidentiality.

   [RFC4522] mandates the use of ESP for authenticating OSPFv3 packets.
   The implementations could also provide support for using AH to
   protect these packets.

   The algorithm requirements for AH and ESP are described in [RFC4835]
   and are not discussed here.

5.
Routing Information Protocol Version 2 (RIPv2)

   RIPv2, originally specified in [RFC1388], then [RFC1723], has been
   updated and published as STD56 [RFC2453]. If the Address Family
   Identifier of the first (and only the first) entry in the RIPv2
   message is 0xFFFF, then the remainder of the entry contains the
   authentication information. The [RFC2453] version of the protocol
   provides for authenticating packets using a simple password of not
   more than 16 octets, in which the password is sent in clear.



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   "RIP-2 MD5 Authentication" [RFC2082] added support for Keyed-MD5
   authentication, where a digest is appended to the end of the RIP
   packet. "RIPv2 Cryptographic Authentication" [RFC4822] obsoleted
   [RFC2082] and added the SHA family of hash algorithms to the list of
   cryptographic authentications that can be used to protect RIPv2,
   whereas [RFC2082] previously specified only the use of Keyed MD5.

5.1
Authentication Scheme Selection

   For RIPv2 implementations to interoperate with the use of security,
   one or more authentication schemes must be supported in common. This
   section specifies the preference for standards conformant RIPv2
   implementations, which desire to utilize the security feature.

   Simple Password is a mandatory to implement scheme as defined in
   [RFC2453] and should only be used when the operator wishes to
   preclude the accidental introduction of a RIP router into the domain.
   This authentication scheme is useful, but not when the operator wants
   to protect RIPv2 message exchange in a potentially hostile
   environment.

   [RFC2082] mandates the use of Keyed-MD5. However, [RFC2082] has been
   obsoleted by [RFC4822] Cryptographic Authentication. Compliant
   implementations must provide support for Keyed-MD5 but should
   recognize that this is superseded by Cryptographic Authentication as
   defined in [RFC4822].

   Implementations should provide support for [RFC4822] Cryptographic
   Authentication as it will likely be the preferred authentication
   method in the future.

5.2 Authentication Algorithm Selection

   For RIPv2 implementations to interoperate, one or more authentication
   algorithms must be supported in common that can be used for
   authentication.

   The keyed MD5 algorithm in [RFC2082] and [RFC4822] must be
   implemented. It is our belief that it will be superseded by HMAC-SHA-
   1 also available in [RFC4822]. Keyed MD5 must be implemented for
   interoperability purposes, but its use may be deprecated in the
   future.

   Implementations should provide support for HMAC-SHA-1 used in
   preference to keyed MD5 the future.

   Operators should consider migration to HMAC-SHA-1 if they want to use
   stronger cryptographic algorithms for authenticating RIPv2 packets.



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   Implementations should consider providing support for HMAC-SHA-
   256/HMAC-SHA-384/HMAC-SHA-512 as these algorithms may be preferred in
   the future.

. Routing Information Protocol for IPv6 (RIPng)

   RIPng [RFC2080] relies on the IPv6 AH and IPv6 ESP to provide
   integrity, authentication, and/or confidentiality.

   The algorithm requirements for AH and ESP are described in [RFC4835]
   and are not discussed here.

. Security Considerations

   The cryptographic mechanisms referenced in this document provide only
   authentication algorithms. These algorithms do not provide
   confidentiality. Encrypting the content of the packet and thereby
   providing confidentiality is not considered in the definition of the
   routing protocols.

   The cryptographic strength of the HMAC depends upon the cryptographic
   strength of the underlying hash function and on the size and quality
   of the key. The feasibility of attacking the integrity of routing
   protocol messages protected by Digests may be significantly more
   limited than that of other data, however preference for one family of
   algorithms over another may also change independently of the
   perceived risk to a particular protocol.

   To ensure greater security, the keys used should be changed
   periodically and implementations must be able to store and use more
   than one key at the same time. Operational experience suggests that
   the lack of periodic rekeying is a source of significant exposure and
   that the lifespan of shared keys in the network is frequently
   measured in years.

   While simple password schemes are well represented in the document
   series and in conformant implementations of the protocols, the
   inability to offer either integrity or identity protection are
   sufficient reason to strongly discourage their use.

   This document concerns itself with the selection of cryptographic
   algorithms for use in the authentication of routing protocol packets
   being exchanged between adjacent routing processes.  The
   cryptographic algorithms identified in this document are not known to
   be broken at the current time, and ongoing cryptographic research so
   far leads us to believe that they will likely remain secure in the
   foreseeable future. We expect that new revisions of this document
   will be issued in the future to reflect current thinking on the



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   algorithms various routing protocols should employ to ensure
   interoperability between disparate implementations.

. Acknowledgements

   We would like to thank Joel Jaeggli for this comments and feedback on
   this draft that resulted in significant improvement of the same.

. IANA Considerations

   This document places no requests to IANA.

10.
References

10.1 Normative References

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

   [ISO]       "Intermediate system to Intermediate system routeing
               information exchange protocol for use in conjunction with
               the Protocol for providing the Connectionless-mode
               Network Service (ISO 8473) ", ISO/IEC 10589:1992

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

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

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

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

   [RFC5340]   Coltun, R., et. al, "OSPF for IPv6", RFC 5340, July
               2008.

   [RFC4835]   Manral, V., "Cryptographic Algorithm Implementation
               Requirements for Encapsulating Security Payload (ESP) and
               Authentication Header (AH)", RFC 4835, April 2007

   [RFC2080]   Malkin, G. and Minnear, R., "RIPng for IPv6", RFC 2080,
               January 1997

   [RFC5310]   Bhatia, M., et. al., "IS-IS Generic
               Cryptographic Authentication", RFC 5310, February 2009

   [RFC5709]   Bhatia, M., Manral, V., et al., "OSPF HMAC-SHA


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               Cryptographic Authentication", RFC 5709, October 2009

10.2
Informative References

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

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

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

   [RFC4522]   Gupta, M. and Melam, N.,"Authentication/Confidentiality
               for OSPFv3", RFC 4522, June 2006

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

   [RFC1723]   Malkin, G., "RIP Version 2 - Carrying Additional
               Information", STD 56, RFC 1723, November 1994.

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

   [SHS]       National Institute of Standards and Technology (NIST),
               FIPS Publication 180-3: Secure Hash Standard, October
               2008.

   Author's Addresses

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

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










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