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Versions: 00 01 02 03 04 05 draft-ietf-mpls-ldp-hello-crypto-auth

Network working group                                          L. Zheng
Internet Draft                                                  M. Chen
Intended status: Standards Track                    Huawei Technologies
Updates: RFC 5036 (if approved)
Expires: April 2011                                     October 8, 2010


                  LDP Hello Cryptographic Authentication

               draft-zheng-mpls-ldp-hello-crypto-auth-00.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
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   document must include Simplified BSD License text as described in





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   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Abstract

   This document introduces a new Cryptographic Authentication TLV
   which is used in LDP Hello message as an optional parameter. It
   enhances the authentication mechanism for LDP by securing the Hello
   message against spoofing attack.

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..................................................2
   2. Cryptographic Authentication TLV..............................4
      2.1. Optional Parameter for Hello Message.....................4
      2.2. Cryptographic Authentication TLV Encoding................4
   3. Processing Hello Message Using Cryptographic Authentication...5
      3.1. Transmission Using Cryptographic Authentication..........6
      3.2. Receipt Using Cryptographic Authentication...............6
   4. Security Considerations.......................................7
   5. IANA Considerations...........................................7
   6. Acknowledgments...............................................8
   7. References....................................................8
      7.1. Normative References.....................................8
      7.2. Informative References...................................8
   Authors' Addresses...............................................9

1. Introduction

   The Label Distribution Protocol (LDP) [RFC 5036] utilizes LDP
   sessions that run between LDP peers. The peers may be directly
   connected at the link level or may be remote. A label switching
   router (LSR) that speaks LDP may be configured with the identity of
   its peers or may discover them using the LDP Hello message sent
   encapsulated in UDP that may be addressed to "all routers on this
   subnet" or to a specific IP address. Periodic Hello messages are
   also used to maintain the relationship between LDP peers necessary
   to keep the LDP session active.




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   Unlike all other LDP messages, the Hello messages are sent using UDP
   not TCP. This means that they cannot benefit from the security
   mechanisms available with TCP. [RFC5036] does not provide any
   security mechanisms for use with Hello messages except to note that
   some configuration may help protect against bogus discovery events.

   Spoofing a Hello packet for an existing adjacency can cause the
   valid adjacency to time out and in turn can result in termination of
   the associated session. This can occur when the spoofed Hello
   specifies a smaller Hold Time, causing the receiver to expect Hellos
   within this smaller interval, while the true neighbor continues
   sending Hellos at the previously agreed lower frequency. Spoofing a
   Hello packet can also cause the LDP session to be terminated
   directly, which can occur when the spoofed Hello specifies a
   different Transport Address, other than the previously agreed one
   between neighbors. Spoofed Hello messages is observed and reported
   as real problem in production networks.

   As described in [RFC5036], the threat of spoofed Basic Hellos can be
   reduced by accepting Basic Hellos only on interfaces to which LSRs
   that can be trusted, and ignoring Basic Hellos not addressed to the
   "all routers on this subnet" multicast group. Spoofing attacks via
   Extended Hellos are potentially more serious threat. An LSR can
   reduce the threat of spoofed Extended Hellos by filtering them and
   accepting only those originating at sources permitted by an access
   list. However, performing the filtering using access lists requires
   LSR resource, and the LSR is still vulnerable to the IP source
   address spoofing.

   This document introduces a new Cryptographic Authentication TLV
   which is used in LDP Hello message as an optional parameter. It
   enhances the authentication mechanism for LDP by securing the Hello
   message against spoofing attack, and an LSR can be configured to
   only accept Hello messages from specific peers when authentication
   is in use.

   Using this Cryptographic Authentication TLV, one or more secret keys
   (with corresponding key IDs) are configured in each system. For each
   LDP Hello packet, the key is used to generate and verify a "message
   digest" or "message hash" that is stored in the LDP Hello packet. A
   sequence number is also carried in each packet to help avoid replay
   attacks.







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2. Cryptographic Authentication TLV

2.1. Optional Parameter for Hello Message

   [RFC5036] defines the encoding for the Hello message. Each Hello
   message contains zero or more Optional Parameters, each encoded as a
   TLV. Three Optional Parameters are defined by [RFC5036]:



         Optional Parameter               Type
        -------------------------------  --------
         IPv4 Transport Address           0x0401
         Configuration Sequence Number    0x0402
         IPv6 Transport Address           0x0403


   This document defines a new Optional Parameter: the Cryptographic
   Authentication parameter. The Cryptographic Authentication TLV
   Encoding is described in section 2.2.


2.2. Cryptographic Authentication TLV Encoding



    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|0|       Auth (0x0404)       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Auth Type   |  Auth Key ID  |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Auth Key/Digest/Hash...                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   - Type: 0x0404 (TBD by IANA), Cryptographic Authentication

   - Length: Specifying the length in octets of the value field.

   - Auth Type: The authentication type in use

       0 - Keyed MD5


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      1 - Meticulous Keyed MD5
      2 - Keyed SHA1
      3 - Meticulous Keyed SHA1
      4 - Keyed SHA-256
      5 - Keyed SHA-384
      6 - Keyed SHA-512
      7-255 - Reserved for future use
   (TBD by IANA)

   - Auth Key ID: The authentication key ID in use for this packet.
      This allows one or more keys to be active simultaneously.

   - Reserved: MUST be set to zero on transmit, and ignored on receipt.

   - Sequence Number: The sequence number for this packet, providing
      protection against replay attacks. The value is incremented
      occasionally. For Meticulous Keyed MD5 and Meticulous Keyed SHA1
      Authentication, this value is incremented for each successive
      packet transmitted for a session.

   - Auth Key/Digest/Hash:

     This field carries the MD5/SHA1/SHA2 key digest/hash for the packet.
     The length of the Auth Key/Digest/Hash varies based on the
     cryptographic algorithm used, which is shown as below:

         Auth type               Length
        ----------------------  ----------
         Keyed MD5              16 bytes
         Meticulous Keyed MD5   16 bytes
         Keyed SHA1             20 bytes
         Meticulous Keyed SHA1  20 bytes
         Keyed SHA-256          32 bytes
         Keyed SHA-384          48 bytes
         Keyed SHA-512          64 bytes

     When calculating the digest/hash, the shared key is stored in this
     field, padding with trailing zeros if needed.

3. Processing Hello Message Using Cryptographic Authentication

   The Cryptographic Authentication mechanisms described in this draft
   are very similar to those used in other protocols. One or more
   secret keys (with corresponding key IDs) are configured in each


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   system. One of the keys is included in a digest or a hash calculated
   over the outgoing LDP Hello packet, but the Key itself is not
   carried in the packet.

   A sequence number is also carried in each packet to help avoid
   replay attacks. The sequence number may be incremented in a circular
   fashion. For most of the authentication scheme in use, the sequence
   number is occasionally incremented (The decision as to when to
   increment the sequence number is implementation dependent and
   outside the scope of this document). Specifically, for Meticulous
   Keyed MD5 and Meticulous Keyed SHA1, the sequence number is
   incremented on every packet.



3.1. Transmission Using Cryptographic Authentication

   Prior to transmitting Hello message, the Auth Type field is set to
   indicate the authentication type in use. The Auth Key ID field is
   set to the ID of the current authentication key. The Sequence Number
   field is set, possibly having been incremented from the last message
   sent according to the scheme in place. The authentication key is
   placed into the Auth Key/Digest field, padding with trailing zeros
   as necessary, for digest/hash calculation.

   An MD5 digest or a SHA1/SHA2 hash is calculated over the entire LDP
   Hello packet. The resulting digest/hash is stored in the Auth
   Key/Digest/Hash field prior to transmission. The secret key is
   replaced by the digest/hash, and MUST NOT be carried in the packet.



3.2. Receipt Using Cryptographic Authentication

   The receiving LSR applies acceptability criteria for received Hellos
   using cryptographic authentication. If the Cryptographic
   Authentication TLV is unknown to the receiving LSR, the received
   packet MUST be discarded according to Section 3.5.1.2.2 of [RFC5036].

   If the Cryptographic Authentication TLV in a received Hello packet
   does not contain a known and acceptable Auth Type value, then the
   received packet MUST be discarded. If the Auth Key ID field does not
   match the ID of a configured authentication key, the received packet
   MUST be discarded.





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   For most of the authentication scheme in use, if the received
   sequence number lies outside of the range of last sequence number
   received to last sequence number received +(Hello Hold Time/Hello
   Interval) inclusive, the received packet MUST be discarded.
   Specifically, for Meticulous Keyed MD5 and Meticulous Keyed SHA1, if
   the received sequence number lies outside of the range of last
   sequence number received+1 to last sequence number received +(Hello
   Hold Time/Hello Interval) inclusive, the received packet MUST be
   discarded.

   The receiving LSR replaces the contents of the Auth Key/Digest/Hash
   field with the authentication key specified by the received Auth Key
   ID field. If the MD5 digest or SHA1/SHA2 hash of the entire LDP
   Hello packet is equal to the received value of the Auth
   Key/Digest/Hash field, the received packet is accepted for other
   normal checks and processing as described in [RFC5036]. Otherwise,
   the received packet MUST be discarded.



4. Security Considerations

   Section 1 of this document describes the security issues arising
   from the use of unsecured LDP Hello messages. In order to combat
   those issues, it is RECOMMENDED that all deployments use the
   Cryptographic Authentication TLV to secure the Hello message.

   The quality of the security provided by the Cryptographic
   Authentication TLV depends completely on the strength of the
   cryptographic algorithm in use, the strength of the key being used,
   and the correct implementation of the security mechanism in
   communicating LDP implementations. Also, the level of security
   provided by the Cryptographic Authentication TLV varies based on the
   authentication type used.



5. IANA Considerations

   IANA maintains a registry of LDP message parameters with a sub-
   registry to track LDP TLV Types. This document request IANA to
   assign a new TLV Types as follows:

   TLV                           Type

   Cryptographic Authentication  0x0404 (TBD)



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   This document also request IANA to assign a new registry titled "LDP
   Hello Authentication Type", its recommended values as follows:

         Value   LDP Hello Authentication Type Name
        -------  -----------------------------------
           0      Keyed MD5
           1      Meticulous Keyed MD5
           2      Keyed SHA1
           3      Meticulous Keyed SHA1
           4      Keyed SHA-256
           5      Keyed SHA-384
           6      Keyed SHA-512
         7-255    Unassigned
   (TBD)

6. Acknowledgments

   The authors would like to thank Liu Xuehu for his work on background
   and motivation for LDP Hello authentication. The authors also would
   like to thank Adrian Farrel, Thomas Nadeau and So Ning for their
   comments.

7. References

7.1. Normative References

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

   [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
             Specification", RFC 5036, October 2007.



7.2. Informative References

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

   [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
             Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
             Authentication", RFC 5709, October 2009.

   [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection",
             RFC 5880, June 2010.


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Authors' Addresses

   Lianshu Zheng
   Huawei Technologies Co., Ltd.
   Huawei Building, No.3 Xinxi Road,
   Hai-Dian District,
   Beijing 100085
   China

   Email: verozheng@huawei.com


   Mach(Guoyi) Chen
   Huawei Technologies Co., Ltd.
   Huawei Building, No.3 Xinxi Road,
   Hai-Dian District,
   Beijing 100085
   China

   Email: mach@huawei.com




























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