Subject: [Ietf-krb-wg] Changes in draft 9 of the preauth framework

From: Sam Hartman <[email-masked]>
Date: Tue, 10 Feb 2009 21:35:46 -0500

Folks, I just posted draft 9 of the pre-authentication framework.

I believe this version is very close to ready for last call.

Here are changes from 08; I'd appreciate comments on these changes,
especially any concerns.

A.1.  Changes since 08

      Fix a number of typos
      Rename anonymous flag to hide-client-name; rename kdc-referals to
      kdc-follow-referrals
      Clarify how anonymous pkinit interacts with KDC verified.
      Introduce AD-fx-fast-armor authorization data to deal with
      unprivileged processes constructing KDC requests.  Note that a TGT
      is always used for armor tickets if the armor field is present; if
      you proxy or validate you'll end up with a TGT armor ticket and
      another ticket in the pa-tgs-req.  Alternatively you can simply
      use the other ticket in the PA-TGS-REQ; weak consensus within WG.
      All KDCs in a realm MUST support FAST if it is to be offered.
      The cookie message is always generated by the KDC.
      Note that the client can trust and need not verify the time stamp
      in the finish message.  This can seed the client's idea of KDC
      time.
      Note that the client name in the finish message may differ from
      the name in the request if referrals are used.
      Note that KDCs should advertize fast in preauth_required errors.
      Armor key is constructed using KRB-FX-CF2.  This is true even in
      the TGS case; there is no security reason to do this.  Using the
      subkey as done in draft 08 would be fine, but the current text
      uses the same procedure both in the TGS and AS case.
      Use a different challenge key in each direction in the encrypted
      challenge option.
      Note that the KDC should process PA-FX-COOKIE before other padata.
      KRB-FX-CF2 uses k1's enctype for the result; change around calling
      order so we pass in subkeys and armor keys as k1 in preference to
      long-term keys or ticket session keys.
      Clarify the relationship between authentication sets and cookies.
      A cookie may not be needed in the first message.  Clarify how this
      interacts with optimistic clients.
      Remove text raising a concern that RFC 3961 may permit ciphertext
      transformations that do not change plaintext: discussion on the
      list came to the conclusion that RFC 3961 does not permit this.
      Remove binding key concept; use the armor key instead.  The cookie
      becomes just an octet string.
      Include PA-FX-ERROR to protect the error information per Dublin.
      Returning preauth_failed in the failed to decrypt encrypted
      challenge seems fine; remove the issue marker
      Add a section describing what goes in the inner and outer request.
      I believe it is redundant but found it useful while putting
      together an implementation proposal.
      Use hyphen rather than underscore in the constants for pre-
      authentication data to be consistent with RFC 4120.
      Add a ticket-checksum to the finished message
      Remove redundant KEY_USAGE_FAST_ARMOR.
      Add protocol constants section for non-IANA registrations and
      flesh out IANA section.
      Clarify that kdc-req-body checksums should always use the outer
      body even for mechanisms like PKINIT that include their own (now
      redundant) checksum.
      Remove mechanism for encapsulating typed data in padata; just
      reflect the value.

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