KARP Working Group                                     Manav Bhatia
   Internet Draft                                       Alcatel-Lucent
   Intended status: Standards Track
   Expires: March, 2011                                 September 2010
                Non IPSec Authentication mechanism for OSPFv3
   Status of this Memo
      This Internet-Draft is submitted to IETF in full conformance
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      Currently OSPFv3 uses IPSec for authenticating the protocol
      packets. This draft proposes an alternative – Generic
      Authentication that can be used so that OSPFv3 does not depend
      upon IPSec for security. The mechanism introduced in this draft
      is generic and can be used by any protocol that currently uses
      IPSec for authentication.
   Conventions used in this document
      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      "OPTIONAL" in this document are to be interpreted as described
      in RFC 2119. [RFC2119]
   Table of Contents
      1. Introduction..................................................2
      2. Basic Operation...............................................4
      3. OSPFv3 Security Association...................................4
      4. Authentication Procedure......................................6
         4.1. Generic Authentication Header............................6
         4.2. Cryptographic Authentication Procedure...................8
         4.3. Cryptographic Aspects....................................8
         4.4. Procedures at the Sending Side..........................10
         4.5. Procedures at the Receiving Side........................10
      5. Generic Authentication Mechanism.............................11
      6. Security Considerations......................................11
      7. IANA Considerations..........................................12
      8. References...................................................12
         8.1. Normative References....................................12
         8.2. Informative References..................................12
   1. Introduction
      Unlike OSPF (Open Shortest Path First) Version 2 [RFC2328] OSPF
      for IPv6 (OSPFv3) [RFC5340], does not have Auth Type and
      Authentication fields in its headers for authenticating the
      protocol packets. It instead relies on the IPv6 Authentication
      Header (AH) [RFC4302] and IPv6 Encapsulating Security Payload
      (ESP) [RFC4303] to provide integrity, authentication, and/or
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      [RFC4552] describes how IPv6 AH/ESP extension headers can be
      used to provide authentication/confidentiality to OSPFv3.
      There however are some environments (mobile ad-hoc), where IPSec
      is difficult to configure and maintain, and this mechanism
      cannot be used.
      [RFC4552] discusses, at length, the reasoning behind using
      manually configured keys, rather than some automated key
      management protocol such as IKEv2 [RFC5996]. The primary problem
      is the lack of suitable key management mechanism, as OSPF
      adjacencies are formed on a one-to-many basis and most key
      management mechanisms are designed for a one-to-one
      communication model. This forces the system administrator to use
      manually configured security associations (SAs) and
      cryptographic keys to provide the authentication and, if
      desired, confidentiality services.
      Regarding replay protection [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
      Since there is no replay protection provided there are a number
      of vulnerabilities in OSPFv3 which have been discussed in
      These can be fixed if we move to a non IPSec method for
      authenticating the OSPFv3 protocol packets.
      Lastly, there is also an issue with using IPSec for
      authenticating OSPFv3 packets where prioritizing certain
      protocol packets over the others becomes difficult. While this
      problem can be solved by employing certain implementation
      tricks, it is an issue that should get addressed.
      This draft proposes a new mechanism that works similar to OSPFv2
      for providing authentication to the OSPFv3 packets and attempts
      to solve the problems described above for OSPFv3.
      Additionally this document describes how HMAC-SHA authentication
      can be used for OSPFv3.
      By definition, HMAC ([RFC2104], [FIPS-198]) requires a
      cryptographic hash function. This document proposes to use any
      one of SHA-1, SHA-256, SHA-384, or SHA-512 [FIPS-180-3] to
      authenticate the OSPFv3 packets.
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      It is believed that [RFC2104] is mathematically identical to
      [FIPS-198] and it is also believed that algorithms in [RFC4634]
      are mathematically identical to [FIPS-180-3].
   2. Basic Operation
      In order to provide authentication for OSPFv3 packets,
      implementations MUST support the Generic Authentication
      extension header described in the subsequent sections.
      This will only be used to provide data integrity and cannot be
      used for confidentiality. If the latter is required then
      implementations MUST use ESP as described in [RFC4552].
      Using this authentication scheme, a session key (either
      statically configured or derived from some master key) is used
      on all the routers attached to a common network. For each OSPFv3
      protocol packet, this key is used to generate and verify a
      "message digest". This digest is carried inside the Generic
      Authentication extension header. The message digest is a one-way
      function of the OSPFv3 protocol packet and the secret key. Since
      the secret key is never sent over the network in the clear,
      protection is provided against passive attacks [RFC1704].
      The algorithms used to generate and verify the digest are
      specified implicitly by the key. In addition, a non decreasing
      sequence number is included in the Generic Authentication Header
      carried along with each OSPFv3 protocol packet to protect
      against replay attacks.
   3. OSPFv3 Security Association
      An OSPFv3 Security Association contains a set of parameters
      shared between any two legitimate OSPFv3 speakers.
      Parameters associated with an OSPFv3 SA:
      Key Identifier (Key ID)
      This is a 32-bit unsigned integer used to uniquely identify an
      OSPFV3 SA, as manually configured by the network operator.
      The receiver determines the active SA by looking at the Key ID
      field in the incoming protocol packet.
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      The sender based on the active configuration, selects the
      Security Association to use and puts the correct Key ID value
      associated with the Security Association in the OSPFV3 protocol
      packet. If multiple valid and active OSPFV3 Security
      Associations exist for a given outbound interface at the time an
      OSPFV3 packet is sent, the sender may use any of those security
      associations to protect the packet.
      Using Key IDs makes changing keys while maintaining protocol
      operation convenient. Each key ID specifies two independent
      parts, the authentication protocol and the authentication key,
      as explained below.
      Normally, an implementation would allow the network operator to
      configure a set of keys in a key chain, with each key in the
      chain having fixed lifetime. The actual operation of these
      mechanisms is outside the scope of this document.
      Note that each key ID can indicate a key with a different
      authentication protocol. This allows multiple authentication
      mechanisms to be used at various times without disrupting an
      OSPFv3 peering, including the introduction of new authentication
      Authentication Algorithm
      This signifies the authentication algorithm to be used with the
      OSPFv3 SA. This information is never sent in cleartext over the
      wire. Because this information is not sent on the wire, the
      implementer chooses an implementation specific representation
      for this information.
      At present, the following values are possible:
      HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512.
      Authentication Key
      This value denotes the cryptographic authentication key
      associated with the OSPFv3 SA. The length of this key is
      variable and depends upon the authentication algorithm specified
      by the OSPFv3 SA.
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   4. Authentication Procedure
   4.1. Generic Authentication Header
      The Generic Authentication Header uses the Next_Header (TBD via
      IANA) in the immediately preceding header, and has the following
   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  Next Header  |   Header Len  |              0                |
   |                            Key ID                             |
   |               Cryptographic Sequence Number                   |
   |                                                               |
   |            Authentication Data (Variable)                     |
   ~                                                               ~
   |                                                               |
   |                                                               |
   |                                                               |
   |                        Padding (Optional)                     |
   ~                                                               ~
   |                                                               |
   |                                                               |
                                  Figure 1
      Next Header
      8 bit selector that identifies the type of header immediately
      following the Generic Authentication Extension Header. Uses the
      same values as the IPv6 Next Header field [RFC2460].
      Header Len
      8-bit selector that indicates the length in 8 octet units of the
      extension header, not including the first 8 octets.
      16-bit reserved field. The value MUST be initialized to zero by
      the sender, and MUST be ignored by the receiver.
      Key ID
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      32-bit field that identifies the algorithm and the secret key
      used to create the message digest carried inside the extension
      Cryptographic Sequence Number
      32-bit non-decreasing sequence number that is used to guard
      against replay attacks.
      Authentication Data
      Variable data that is carrying the digest of the protocol
      This MUST be used with IPv6 in order to preserve IPv6 8-octet
      alignment. If HMAC-SHA-1 is being used as the authentication
      algorithm then the authentication data is of 20 bytes. Add to
      this 1 byte of the next header, 1 byte of the header length, the
      2 reserved bytes, 4 bytes for the cryptographic sequence number
      4 bytes of the Key ID and we get 32 bytes. Since this is already
      aligned to an 8 octet boundary no padding is required. However,
      if the authentication algorithm is HMAC-SHA-256 then the total
      size comes to 44 bytes, which is not aligned. In this case 4
      bytes of padding is used.
      The following diagram illustrates the OSPFv3 packet before and
      after applying this extension header.
      Packet format before applying Generic Authentication Header:
            |orig IP header  |      OSPFv3  Payload         |
            |(any options)   |                              |
      Packet format after applying Generic Authentication Header:
            |orig IP header  | Generic Auth | OSPFv3  Payload  |
            |(any options)   |    header    |                  |
                             |<----------- integrity --------->|
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   4.2. Cryptographic Authentication Procedure
      As noted earlier the algorithms used to generate and verify the
      message digest are specified implicitly by the secret key. This
      specification discusses the computation of OSPFv3 Cryptographic
      Authentication data when any of the NIST SHS family of
      algorithms is used in the Hashed Message Authentication Code
      (HMAC) mode.
      The currently valid algorithms (including mode) for OSPFv3
      Cryptographic Authentication include:
      Of the above, implementations of this specification MUST include
      support for at least:
      and SHOULD include support for:
      and MAY also include support for:
   4.3. Cryptographic Aspects
      In the algorithm description below, the following nomenclature,
      which is consistent with [FIPS-198], is used:
      H is the specific hashing algorithm (e.g. SHA-256).
      K is the Authentication Key for the OSPFv3 security association.
      Ko is the cryptographic key used with the hash algorithm.
      B is the block size of H, measured in octets rather than bits.
      Note that B is the internal block size, not the hash size.
           For SHA-1 and SHA-256:   B == 64
           For SHA-384 and SHA-512: B == 128
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      L is the length of the hash, measured in octets rather than
      XOR is the exclusive-or operation.
      Opad is the hexadecimal value 0x5c repeated B times.
      Ipad is the hexadecimal value 0x36 repeated B times.
      Apad is the hexadecimal value 0x878FE1F3 repeated (L/4) times.
      Implementation Note:
      This definition of Apad means that Apad is always the same
      as the hash output.
      (1)Preparation of the Key
         In this application, Ko is always L octets long.
         If the Authentication Key (K) is L octets long, then Ko is
         equal to K.  If the Authentication Key (K) is more than L
         octets long, then Ko is set to H(K).  If the Authentication
         Key (K) is less than L octets long, then Ko is set to the
         Authentication Key (K) with zeros appended to the end of the
         Authentication Key (K) such that Ko is L octets long.
      (2)First Hash
         First, the OSPFv3 packet's Generic Authentication Extension
         Data field is filled with the value Apad.
         Then, a first hash, also known as the inner hash, is computed
         as follows:
                 First-Hash = H(Ko XOR Ipad || (OSPFv3 Packet))
      (3)Second Hash
         Then a second hash, also known as the outer hash, is
         computed as follows:
                 Second-Hash = H(Ko XOR Opad || First-Hash)
         The result Second-Hash becomes the authentication data that
         is sent in the Authentication Data field of the Generic
         Authentication extension header. The length of the
         authentication data is always identical to the message
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         digest size of the specific hash function H that is being
         This also means that the use of hash functions with larger
         output sizes will also increase the size of the OSPFv3 packet
         as transmitted on the wire.
   4.4. Procedures at the Sending Side
      An appropriate OSPFv3 SA is selected for use with an outgoing
      OSPFv3 protocol packet. This is done based on the active key at
      that instant. If OSPFV3 is unable to find an active key, then
      the packet MUST be discarded.
      If OSPFV3 is able to find the active key, then the key gives the
      authentication algorithm (HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384
      or HMAC-SHA-512) that needs to be applied on the packet.
      An implementation MUST construct a pseudo Generic Authentication
      extension header before it begins the authentication process. It
      must set the Next Header to 89, to indicate an OSPF packet. The
      authentication data is computed as explained in the previous
      The Header length is set as per the authentication algorithm
      that is being used. It is, for example, set to 3 for
      HMAC-SHA-1 and 5 for HMAC-SHA-256.
      The key ID and the cryptographic sequence number is filled.
      Appropriate padding, based on the authentication algorithm being
      employed, must be used.
      The result of the authentication algorithm is placed in the
      Authentication data.
   4.5. Procedures at the Receiving Side
      The appropriate OSPFv3 SA is identified by looking at the Key ID
      from the Generic Authentication extension header from the
      incoming OSPFv3 protocol packet
      Authentication algorithm dependent processing needs to be
      performed, using the algorithm specified by the appropriate
      OSPFv3 SA for the received packet.
      Before an implementation performs any processing it needs to
      save the values of the Authentication Value field in the Generic
      Authentication extension header.
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      It should then set the Authentication Value field with Apad
      before the authentication data is computed. The calculated data
      is compared with the received authentication data in the packet
      and the packet is discarded if the two do not match. In such a
      case, an error event SHOULD be logged.
      An implementation MAY have a transition mode where it includes
      the Generic Authentication extension header in the packets but
      does not verify this information. This is provided as a
      transition aid for networks in the process of migrating to the
      new generic authentication based authentication schemes.
   5. Generic Authentication Mechanism
      The extension header described in this document can also be used
      by any other protocol that desires integrity protection. All it
      needs to do is to compute the digest over that protocol packet
      and carry it inside the Generic Authentication extension header
      as described in this document.
   6. Security Considerations
      The document proposes extensions to OSPFv3 which would make it
      more secure than what it is today. It does not provide
      confidentiality as a routing protocol contains information
      that does not need to be kept secret. It does, however, provide
      means to authenticate the sender of the packets which is of
      interest to us.
      It should be noted that authentication method described in this
      document is not being used to authenticate the specific
      originator of a packet, but is rather being used to confirm that
      the packet has indeed been issued by a router which had access
      to the password.
      The mechanism described here is not perfect and does not need to
      be perfect. Instead, this mechanism represents a significant
      increase in the work function of an adversary attacking the
      OSPFv3 protocol, while not causing undue implementation,
      deployment, or operational complexity.
      There is a transition mode suggested where routers can ignore
      the Generic Authentication extension header information carried
      in the protocol packets. The operator must ensure that this mode
      is only used when migrating to the new Generic Authentication
      based scheme as this leaves the router vulnerable to an attack.
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   7. IANA Considerations
      The Generic Authentication extension header number is assigned
      by IANA out of the IP Protocol Number space (and as recorded at
      the IANA web page at
      http://www.iana.org/assignments/protocol-numbers) is: TBD.
   8. References
   8.1. Normative References
      [RFC2119] Bradner, S.,"Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
      [RFC2460] Deering, S., et. al, "Internet Protocol, Version 6
                (IPv6) Specification", RFC 2460, December 1998.
      [FIPS-180-3] US National Institute of Standards & Technology,
                "Secure Hash Standard (SHS)", FIPS PUB 180-3, October
      [FIPS-198] US National Institute of Standards & Technology, "The
                Keyed-Hash Message Authentication Code (HMAC)", FIPS
                PUB 198, March 2002.
   8.2. Informative References
      [RFC1704] Haller, N. and R. Atkinson, "On Internet
                Authentication", RFC 1704, October 1994.
      [RFC2104] Krawczk, H., "HMAC: Keyed-Hashing for Message
                Authentication", RFC 2104, February 1997.
      [RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
      [RFC5340] Coltun, R., et. al., "OSPF for Ipv6", RFC 5340, July
      [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
                December 2005.
      [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
                RFC 4303, December 2005.
      [RFC5996] Kaufman, C., et. al., "Internet Key Exchange Protocol
                Version 2 (IKEv2)",  RFC 5996, September 2010.
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      [RFC4552] Gupta, M. and Melam, N.,
                "Authentication/Confidentiality for OSPFv3", RFC 4552,
                June 2006
      [RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash
                Algorithms (SHA and HMAC-SHA)", RFC 4634, July 2006.
      [crypto-issues] Bhatia, M., et. al., " Issues with existing
                Cryptographic Protection Methods for Routing
                Protocols", Work in Progress
      Author's Addresses
      Manav Bhatia
      Email: manav.bhatia@alcatel-lucent.com
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