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Versions: 00 01 02 03 04 05                                             
Working Group                                                U. Chunduri
Internet-Draft                                                   A. Tian
Intended status: Informational                                A. Keranen
Expires: April 23, 2014                                         Ericsson
                                                              T. Kivinen
                                                           INSIDE Secure
                                                        October 20, 2013

                KARP KMP: Simplified Peer Authentication


   This document describes the usage of Router Fingerprint
   Authentication (RFA) with public keys as a potential peer
   authentication method with KARP pair wise and group Key Management
   Protocols (KMPs).  The advantage of RFA is, it neither requires out-
   of-band, mutually agreeable symmetric keys nor a full PKI based
   system (trust anchor or CA certificates) for mutual authentication of
   peers with KARP KMP deployments.  Usage of Router Fingerprints give a
   significant operational improvement from symmetric key based systems
   and yet provide a secure authentication technique.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 23, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Router Fingerprint  . . . . . . . . . . . . . . . . . . . . .   4
   3.  Usage of Router Fingerprints with KARP KMP  . . . . . . . . .   4
   4.  Publishing Router Fingerprints  . . . . . . . . . . . . . . .   5
   5.  Scope of Fingerprints usage with RPs  . . . . . . . . . . . .   6
   6.  Fingerprint Revocation  . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. Appendix A  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Applicable Authentications methods . . . . . . . . . . .   7
       10.1.1.  Symmetric key based authentication . . . . . . . . .   7
       10.1.2.  Asymmetric key based authentication  . . . . . . . .   8
       10.1.3.  EAP based authentication . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Usage of IKEv2[RFC5996] as the KMP for with specific extensions for
   pair wise routing protocols (RPs) is described in [mahesh-karp-rkmp].
   Also IKEv2 based KMP for group keying RPs is described in [hartman-
   karp-mrkmp].  With proliferation of authentication methods supported
   by IKEv2, this draft explores a simple and secure peer authentication
   method, which can be potentially used for all KARP KMP deployments.

   Currently operators don't often change the manual keys deployed for
   protecting RP messages because of various reasons as noted in
   Section 2.3 of KARP threat document [RFC6862].  One of the KARP WG
   goals is to define methods to support key changes for all RPs which
   use either Manual Key Management (MKM) or KMP without much
   operational overhead.

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   Apart from Peer's identity verification, authentication and parameter
   negotiation, deployment of KMP can be more useful, when it comes to
   rekey the keys used by RPs.  Rekeying can be achieved without the
   operator's intervention and as per the provisioned rekey policy.  But
   for operators, usage of IKEv2 KMP opens up numerous possibilities for
   peer authentication and manual symmetric keys are not only used for
   bootstrapping KMP, but used for peer authentication.  Various other
   peer authentication mechanisms with advantages/drawbacks of each
   mechanism are described in the Section 10.1 of this document.

   If symmetric pre-shared keys are used by IKEv2 KMP to authenticate
   the peer before generating the shared key(s); apart from other issues
   with symmetric keys, the problem still remain the same when it comes
   to changing these keys.

   To reduce operational costs for changing keys at peering points with
   relatively large number of RP peers, this document describes the use
   of one of the available IKEv2 KMP peer authentication methods with
   raw public keys.  The hash of these encoded public keys is called as
   Router Fingerprints and the authentication method is called Router
   Fingerprint Authentication (RFA) in rest of the document.  The RFA
   method in conjunction with KARP KMPs require, neither out-of-band
   symmetric keys nor a fully functional PKI based system with trust
   anchor certificates as explained further in Section 2.

   Section 2 describes the Router Fingerprints in the context of various
   KMPs and specifically for IKEv2 KMP.  Generation and usage of the
   Router Fingerprints is described in Section 3 and Section 4 describes
   a reliable method for publishing the Router Fingerprints.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Acronyms

   CRL     -  Certificate Revocation List.

   EBGP    -  External BGP (BGP connection between external peers).

   EE      -  End Entity.

   IBGP    -  Internal BGP (BGP connection between internal peers).

   KMP     -  Key Management Protocol (auto key management).

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   MKM     -  Manual Key management Protocols.

   PAD     -  Peer Authorization Database.

   RFA     -  Router Fingerprint Authentication.

   RP      -  Routing Protocol.

2.  Router Fingerprint

   Router Fingerprint is a sequence of bytes used to authenticate the
   public key before using the same public key to authenticate the peer
   in the context of KARP KMP.

   Various forms of fingerprint mechanisms based on the public keys are
   already in use as defined in [RFC4252] and [RFC4253].  Fingerprints
   are also used primarily for root key authentication in X.509 based
   PKI [RFC5280].  This documents only highlights the usage of raw
   public key based authentication mechanism already defined in
   [RFC5996] for KARP deployments.

   To generate a fingerprint:

   1.  A router needs to generate an asymmetric Private/Public key pair.
       Asymmetric crypto algorithms based on RSA [RFC3447] or for
       shorter and still secure keys Elliptic Curve Cryptography (ECC)
       [RFC4492] can be used for generating the Private/Public key pair.

   2.  Once the Asymmetric key pair is generated, the public key can be
       encoded with any additional data (specific to the router or
       routing instance) and can be in the form of more easily
       administrable X.509 PKI Certificate profile and to be specific as
       specified in the SubjectPublicKeyInfo structure in Section 4.1 of
       [RFC5280].  This does not force use of X.509 or full compliance
       with [RFC5280] since formatting any public key as a
       SubjectPublicKeyInfo is relatively straightforward and well
       supported by libraries.

   3.  The result should be hashed with a cryptographic hash function,
       preferably SHA-256 or hash functions with similar strength (see
       more discussion on choosing preferred hash function in
       Section 8).

   The fingerprint generated is not a secret and can be distributed
   publicly.  This is further discussed in Section 4.

3.  Usage of Router Fingerprints with KARP KMP

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   To use Router Fingerprints authentication with KARP KMP, a Private/
   Public key-pair MUST be generated by the router as specified in
   Section 2.  To deploy RFA method more widely -

   1.  type of public keys supported should be generic; for e.g.,
       support for raw Elliptic Curve public keys and

   2.  more generic encoding formats should be supported for carrying
       the raw public keys other than currently defined PKCS #1.

   [I-D.kivinen-ipsecme-oob-pubkey] enhances support for other types of
   public keys and also defines new encoding format to carry the public
   key fingerprint in the CERT payload.  For RPs to use Router
   Fingerprint Authentication in the context of IKEv2 MUST follow the
   encoding format as specified in [I-D.kivinen-ipsecme-oob-pubkey].

   For RFA, the public key received is in the form of
   SubjectPublicKeyInfo structure of X.509 PKI profile and the Peer
   Authorization Database (PAD) entry [RFC4301] MUST contain the
   published fingerprint of the peer.

4.  Publishing Router Fingerprints

   The router fingerprint generated is not a secret and can be exchanged
   out-of-band or can be distributed publicly.  Please refer to
   Section 5 for the generic usage and scope of the RFA in routing
   environments.  In the case of inter-domain routing using EBGP
   [RFC4271], if the routers are outside of the SIDR [I-D.ietf-sidr-
   bgpsec-overview] environment, fingerprint can also be exchanged out-
   of-band through Service Level Agreements (SLAs) at the RP peering

   [RFC6920] defines a "Named Information" identifier, which provides a
   set of standard ways to use hash function outputs in names.  As there
   are many ways to publish fingerprints in an unambiguous manner (e.g.,
   as defined in Section 5 of [RFC4572]); on the WG consensus, KARP
   deployments MUST use the method described in [RFC6920] for
   interoperability.  A KARP KMP deployment using router fingerprints
   need to resort to out-of-band public key validation procedure to
   verify authenticity of the keys being used.  The router fingerprints
   MUST be part of the KMP PAD to validate the public key received in
   the KMP messages.

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5.  Scope of Fingerprints usage with RPs

   The fingerprint method described in this document in general is more
   suitable for intra domain deployments.  This includes KMP usage for
   e.g., for IBGP [RFC4271] and LDP [RFC5036] peers, where KARP KMP can
   be deployed without having to configure either manual pre-shared keys
   to bootstrap KMP or full PKI with trust anchor certificates.  Also
   KMPs for group keying RPs can use this method for authenticating the
   peers in the group.  This method also can be potentially used between
   EBGP [RFC4271] speakers outside of the SIDR ([I-D.ietf-sidr-bgpsec-
   overview]) deployment scope, where full PKI infrastructure is not
   available to deploy with KARP KMP and at the same time, still
   operators want to avoid provisioning manual keys.

6.  Fingerprint Revocation

   The idea of RFA in the context of KARP KMP is to deploy a better
   authentication method than the mutually shared symmetric keys between
   two routers.  This SHOULD be used especially where number of peers
   using this method is relatively smaller and operationally manageable.
   Any changes in the router fingerprints SHOULD be administered
   manually by the operator.  For e.g., to revoke the compromised key
   operator simply need to remove the fingerprint from the PAD, which do
   require and update to the PAD of all possible nodes in the network
   where this node was talking to.  Quite often those configurations are
   already pushed to routers by some kind of management tool, so it is
   completely possible to do this quite easily.

   When there are a large number of peers, the need for router
   fingerprint changes may increase.  This may be for reasons of key
   compromises or other potential changes to the routers.  In such
   environments, operators SHOULD look to full PKI with trust anchor
   certificates and CRL profiles as specified in the [RFC5280].  In this
   context, RFA mechanism should be only seen as substantial improvement
   from mutually shared manual keying authentication methods.

7.  IANA Considerations

   This document defines no new namespaces.

8.  Security Considerations

   If collision attacks are perceived as a threat, the hash function to
   generate the fingerprints MUST also possess the property of
   collision-resistance.  To mitigate preimage attacks, the
   cryptographic hash function used for a fingerprint MUST possess the
   property of second preimage resistance.

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   For deploying RFA authentication method, generated fingerprints MUST
   not be truncated to make those short as to preserve the relevant
   properties of the hash function against brute-force search attacks.

   Considering the above facts, it's recommended to use SHA-256 or
   similar hash functions with good security properties to generate the

9.  Acknowledgements

   The authors would like to thank Jari Arkko for initial and valuable
   discussions on operationally simplified authentication methods in
   general and RFA mechanism as described in this document in
   particular.  Authors would like to acknowledge Joel Halpern for
   supporting this work and providing continuous feedback on the draft,
   including the usefulness of this approach in routing environments.

10.  Appendix A

10.1.  Applicable Authentications methods

   One advantage that IKEv2 provides is the largest selection of key
   management and parameter coordination authentication methods suitable
   for various environments.  The goal of this section is to look at
   various KMP authentication options available and recommend suitable
   options for use in negotiating keys and other parameters for routing
   protocol protection.

   As some of the authentication mechanisms are optional in IKEv2, one
   mandatory authentication mechanism from the list below needs to be
   selected for routing environments to ensure inter-operability and
   quicker adoption.  This section attempts to summarize the available
   options and constraints surrounding the options.

10.1.1.  Symmetric key based authentication

   IKEv2 [RFC5996] allows for authentication of the IKEv2 peers using a
   symmetric pre-shared key.  For symmetric pre-shared key peer
   authentication, deployments need to consider the following as per

   1.  Deriving a shared secret from a password, name, or other low-
       entropy source is not secure.  These sources are subject to
       dictionary and social-engineering attacks, among others.

   2.  The pre-shared key should not be derived solely from a user-
       chosen password without incorporating another source of

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   3.  If password-based authentication is used for bootstrapping the
       IKE_SA, then one of the EAP methods as described in
       Section 10.1.3 needs to be used.

   One of the IPsecME WG charter goals is to provide IKEv2 [RFC5996] a
   secure password authentication mechanism which is protected against
   off-line dictionary attacks, without requiring the use of
   certificates or Extensible Authentication Protocol (EAP), even when
   using the low-entropy shared secrets.  There are couple of documents
   which try to address this issue and the work is still in progress.

10.1.2.  Asymmetric key based authentication

   Another peer authentication mechanism IKEv2 uses is asymmetric key
   certificates or public key signatures.  This approach relies on a
   Public Key Infrastructure using X.509 (PKIX) Certificates.  If this
   can be deployed for IKEv2 peer authentication, it will be one of the
   most secure authentication mechanisms.  With this authentication
   option, there is no need for out-of-band shared keys between peers
   for mutual authentication.

   Apart from RSA and DSS digital signatures for public key
   authentication provided by IKEv2, [RFC4754] introduces Elliptic Curve
   Digital Signature Algorithm (ECDSA) signatures.  ECDSA provides
   additional benefits including computational efficiency, small
   signature sizes, and minimal bandwidth compared to other available
   digital signature methods.

10.1.3.  EAP based authentication

   In addition to supporting authentication using shared secrets and
   public key signatures, IKEv2 also supports authentication based on
   the Extensible Authentication Protocol (EAP), defined in [RFC3748].
   EAP is an authentication framework that supports multiple
   authentication mechanisms.  IKEv2 provides EAP authentication because
   public key signatures and shared secrets are not flexible enough to
   meet the requirements of many deployment scenarios.  For KARP KMP,
   EAP-Only Authentication in IKEv2 as specified in [RFC5998] can be

   By using EAP, IKEv2 KMP can leverage existing authentication
   infrastructure and credential databases, because EAP allows users to
   choose a method suitable for existing credentials.  Routing protocols
   today use password-based pre-shared keys to integrity protect the
   routing protocol messages.  The same pre-shared key can be used to
   bootstrap the KMP and as a potential authentication key in KMP.  With
   appropriate password based EAP methods, stronger keys can be
   generated without using certificates.

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   For authenticating the nodes running routing protocols, EAP and the
   IKEv2 endpoints are co-located (so no separate EAP server required).
   When EAP is deployed, authenticating the IKEv2 responder using both
   EAP and public key signatures could be redundant.  EAP methods that
   offer mutual authentication and key agreement can be used to provide
   responder authentication in IKEv2 completely based on EAP.

   Section 4 of [RFC5998] lists safe EAP methods to support
   EAP_ONLY_AUTHENTICATION.  For routing protocols deployment, because
   an EAP server is co-located with IKEv2 responder, channel binding
   capability of the selected EAP method is irrelevant.  Various
   qualified mutual authentication methods are listed in [RFC5998]; of
   these, a password based methods [RFC4746], [RFC5931], [RFC6124] can
   offer potential EAP alternative for pre-shared key only

11.  References

11.1.  Normative References

              Chunduri, U., Tian, A., and J. Touch, "A framework for RPs
              to use IKEv2 KMP", draft-chunduri-karp-using-ikev2-with-
              tcp-ao-05 (work in progress), July 2013.

              Kivinen, T., Wouters, P., and H. Tschofenig, "More Raw
              Public Keys for IKEv2", draft-kivinen-ipsecme-oob-
              pubkey-05 (work in progress), October 2013.

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

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC
              5996, September 2010.

11.2.  Informative References

              Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router
              Key Management Protocol (MaRK)", draft-hartman-karp-
              mrkmp-05 (work in progress), September 2012.

              Hartman, S. and D. Zhang, "Operations Model for Router
              Keying", draft-ietf-karp-ops-model-09 (work in progress),
              October 2013.

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              Lepinski, M. and S. Turner, "An Overview of BGPSEC",
              draft-ietf-sidr-bgpsec-overview-03 (work in progress),
              July 2013.

              Jethanandani, M., Weis, B., Patel, K., Zhang, D., Hartman,
              S., Chunduri, U., Tian, A., and J. Touch, "Negotiation for
              Keying Pairwise Routing Protocols in IKEv2", draft-mahesh-
              karp-rkmp-04 (work in progress), February 2013.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [RFC3618]  Fenner, B. and D. Meyer, "Multicast Source Discovery
              Protocol (MSDP)", RFC 3618, October 2003.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
              3748, June 2004.

   [RFC4107]  Bellovin, S. and R. Housley, "Guidelines for Cryptographic
              Key Management", BCP 107, RFC 4107, June 2005.

   [RFC4252]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, January 2006.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, January 2006.

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

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492, May 2006.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572, July 2006.

   [RFC4746]  Clancy, T. and W. Arbaugh, "Extensible Authentication
              Protocol (EAP) Password Authenticated Exchange", RFC 4746,
              November 2006.

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   [RFC4754]  Fu, D. and J. Solinas, "IKE and IKEv2 Authentication Using
              the Elliptic Curve Digital Signature Algorithm (ECDSA)",
              RFC 4754, January 2007.

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

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440, March

   [RFC5931]  Harkins, D. and G. Zorn, "Extensible Authentication
              Protocol (EAP) Authentication Using Only a Password", RFC
              5931, August 2010.

   [RFC5998]  Eronen, P., Tschofenig, H., and Y. Sheffer, "An Extension
              for EAP-Only Authentication in IKEv2", RFC 5998, September

   [RFC6124]  Sheffer, Y., Zorn, G., Tschofenig, H., and S. Fluhrer, "An
              EAP Authentication Method Based on the Encrypted Key
              Exchange (EKE) Protocol", RFC 6124, February 2011.

   [RFC6518]  Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP) Design Guidelines", RFC 6518,
              February 2012.

   [RFC6862]  Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
              Authentication for Routing Protocols (KARP) Overview,
              Threats, and Requirements", RFC 6862, March 2013.

   [RFC6920]  Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
              Keranen, A., and P. Hallam-Baker, "Naming Things with
              Hashes", RFC 6920, April 2013.

Authors' Addresses

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   Uma Chunduri
   300 Holger Way
   San Jose, California  95134

   Phone: +1 (408) 750-5678
   Email: uma.chunduri@ericsson.com

   Albert Tian
   300 Holger Way
   San Jose, California  95134

   Phone: +1 (408) 750-5210
   Email: albert.tian@ericsson.com

   Ari Keranen
   Hirsalantie 11
   Jorvas  02420

   Email: ari.keranen@ericsson.com

   Tero Kivinen
   INSIDE Secure
   Eerikinkatu 28
   Helsinki  00180

   Email: kivinen@iki.fi

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