Subject: [Ietf-krb-wg] FAST comment

From: Nicolas Williams <[email-masked]>
Date: Tue, 9 Jun 2009 01:38:36 -0500

- KRB-FX-CF2() takes two keys and produces a third, but it's not clear
   what the enctype of the result should be.

   Either derive the enctype of the resulting key from the enctypes of
   the input keys or else make the result enctype an input argument.  In
   the latter case, clarify what that input should be in all cases where
   KRB-FX-CF2() is used.

So far that's my most significant comment.  I've got some nits to make.

Nico
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From: Sam Hartman <[email-masked]>
Date: Tue, 09 Jun 2009 11:45:08 -0400

>>>>> "Nicolas" == Nicolas Williams <[email-masked]> writes:

    Nicolas>  - KRB-FX-CF2() takes two keys and produces a third, but
    Nicolas> it's not clear what the enctype of the result should be.

Quoting the text:
Quoting the top of page 18:

   Here the counter value 1, 2, 3 and so on are encoded as a one-octet
   integer.  The pseudo-random() operation is specified by the enctype
   of the protocol key.  PRF+() uses the counter to generate enough bits
   as needed by the random-to-key() [RFC3961] function for the
   encryption type specified for the resulting key; unneeded bits are
   removed from the tail.  Unless otherwise specified, the resulting
   enctype of KRB-FX-CF2 is the enctype of k1.

I believe that's well defined.  Conceptually the resulting enctype is
an input, but it has a default value which is always used in this
spec.
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