RFC 3129 (rfc3129) - Page 2 of 6

Requirements for Kerberized Internet Negotiation of Keys

RFC 3129                 Requirements for KINK                 June 2001


   in practice.  While IKE does allow for pre-shared symmetric keys, key
   distribution is required between all peers -- an O(n^2) problem --
   which is problematic for large deployments.

   Kerberos (RFC 1510) provides a mechanism for trusted third party
   authentication for clients and servers.  Clients authenticate to a
   centralized server -- the Key Distribution Center -- which in turn
   issues tickets that servers can decrypt thus proving that the client
   is who it claims to be.  One of the elements of a Kerberos ticket is
   a session key which is generated by the KDC which may be used by the
   client and server to share a secret.  Kerberos also allows for both
   symmetric key authentication, as well as certificate based public key
   authentication (PKinit).  Since the authentication phase of Kerberos
   is performed by the KDC, there is no need to perform expensive DH or
   X.509 certificate signatures/verification operations on servers.
   While clients may authenticate using X.509 certificates, the
   authentication phase can be amortized over the lifetime of the
   credentials.  This allows a single DH and certificate exchange to be
   used to key security associations with many servers in a
   computationally economic way.  Kerberos also support clients with
   symmetric keys but unlike IKE, the symmetric keys are stored in the
   KDC making the number of keys an O(n) problem rather than O(n^2).
   Kerberos also allows security policy to be managed in a more
   centralized fashion, rather than expecting each potentially
   untrustworthy peer to abide by stated security policies of an
   organization.

   The KINK working group takes these basic features of Kerberos and
   uses them to its advantage to create a protocol which can establish
   and maintain IPsec security associations (RFC 2401).  It should be
   noted that KINK is not a replacement for IKE.  IKE has one property
   which KINK cannot reproduce:  the ability for two peers to mutually
   authenticate and exchange keys without the need for an actively
   participating third party.  However, there are many situations where
   a trusted third party which proxies authentication is viable, and in
   fact desirable.

   While Kerberos specifies a standard protocol between the client and
   the KDC to get tickets, the actual ticket exchange between client and
   server is application specific.  KINK is intended to be an
   alternative to requiring each application having its own method of
   transporting and validating service tickets using a protocol which is
   efficient and tailored to the specific needs of Kerberos and the
   applications for which it provides keying and parameter negotiation.

   Given the above, a new general keying protocol which leverages the
   scalability of Kerberos is desirable.  The working group's first task
   is to define this protocol and define an domain of interpretation for



Thomas                       Informational