Subject: [Ietf-krb-wg] draft-ietf-krb-wg-gss-cb-hash-agility-06

From: Simon Josefsson <[email-masked]>
Date: Thu, 31 Mar 2011 23:14:19 +0200

Shawn, all,

On the flight back I implemented your draft in GNU GSS and it seems to
work fine.  I haven't done any interop testing, were there other
implementations?  I noticed one nit though.

The document says

      data-value

         The output obtained by applying the Kerberos V get_mic()
         operation [RFC3961], using the sub-session key from the
         authenticator and key usage number 43, to the channel binding
         data as described in [RFC4121], section 4.1.1.2 (using get_mic
         instead of MD5).

I don't think this works for two separate reasons:

1) There is not always a sub-session key.

2) It is not clear which get_mic operation is used.  There are many to
   chose from.

I suggest to resolve this as follows:

1) Specify that the subkey is used when present, otherwise the key in
   the ticket is used.

2) The get_mic algorithm should be the "required checksum mechanism" of
   the encryption type of the key that is used.

Text to achieve this could be:

         The output obtained by applying the Kerberos V get_mic
         operation [RFC3961] with key usage number 43, to the channel
         binding data as described in [RFC4121], section 4.1.1.2 (using
         get_mic instead of MD5).  The key used is the sub-session key
         from the authenticator, if it is present, otherwise the key
         used is the session key from the ticket.  The get_mic algorithm
         is chosen as the "required checksum mechanism" for the
         encryption type of the key used.

Otherwise the document seems fine.

/Simon
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