Subject: [Ietf-krb-wg] Pkinit alg agility: anonymous principal

From: Sam Hartman <[email-masked]>
Date: Tue, 20 Sep 2011 08:49:07 -0400

In this message I'm wearing the hat of someone debugging pkinit
implementations, not my chair hat.

Hi.

As part of RFC 6112 processing, the KDC transforms the principal
WELLKNOWN/ANONYMOUS@TGS_REALM to WELLKNOWN/ANONYMOUS@WELLKNOWN:ANONYMOUS
at least some of the time.  I cannot remember whether a KDC is permitted
to return the local realm in the anonymous pkinit case.

It's quite important for the KDF that the server and client pass the
same value into party_u_info so you get the same key on the server and
client.

I believe that we should clarify which value should be used in the KDF.

I think the following text from RFC 6112 means that a KDC MUST issue
tickets with the WELLKNOWN:ANONYMOUS realm when anonymous pkinit is
used:

   In this specification, the client realm in the anonymous ticket is
      the anonymous realm name when anonymous PKINIT is used to obtain the
         ticket.  The client realm is the client's real realm name if the
	    client is authenticated using the client's long-term keys.  Note that
	       the membership of a realm can imply a member of the community
	          represented by the realm.

Thus, I think canonicalizing party_u_info to either principal is
acceptable. I propose that when anonymous pkinit is used we canonicalize
party_u_info to WELLKNOWN/ANONYMOUS@WELLKNOWN:ANONYMOUS. 

I'd appreciate comments.

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