Subject: Re: [Ietf-krb-wg] resolving KRB-FX-CF2 and DES random-to-key ambiguities

From: Sam Hartman <[email-masked]>
Date: Thu, 07 Oct 2010 15:37:49 -0400

Tom, I don't think it is reasonable for the preauth framework draft to
update the RFC 3961 operations.  I think that should be done elsewhere.
I'm happy to include an implementation note in the test vectors
appendix.
So, I would be happy to include something like 

In generating these test vectors, the random-to-key operation is assumed
      to be the transformation that Section 6.3.1 of RFC 3961 specifies
      for expanding a group of 56 bits into 64 bits.  (This
      transformation is one third of the triple DES random-to-key
      operation.)  The key generation seed length for des-cbc-md5,
      des-cbc-md4, and des-cbc-crc is 7 bytes.  The operation called
      des_random_to_key() in RFC 3961 is assumed to be used only for the
      string-to-key operation and not for the random-to-key operation.

I don't think the text you propose for 5.1 is appropriate for this
draft, especially after approval, so I do not support including it.  I
would support an update to RFC 3961 that included that text.  I would
not support a normative reference from the preauth framework to such an
update.
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From: Tom Yu <[email-masked]>
Date: Thu, 07 Oct 2010 16:06:35 -0400

> not support a normative reference from the preauth framework to such an

I'll grant that adding an "Updates: 3961" was probably too ambitious
for this change, and I am willing to move that update to another
document.  Also, having thought about it some more, the final sentence
about des_random_to_key() is not quite accurate, and we should omit
it.  I suggest the following change to Appendix A:

Delete the last sentence from this paragraph:

   Interoperability testing also demonstrated ambiguity surrounding the
   DES random-to-key operation.  The random-to-key operation is assumed
   to be distribute 56 bits into high-7-bits of 8 octets and generate
   parity.

and replace it with the following text:

   In generating these test vectors, the DES random-to-key operation
   is assumed to be the transformation that Section 6.3.1 of RFC 3961
   specifies for expanding a group of 56 bits into 64 bits.  (This
   transformation is one third of the triple DES random-to-key
   operation, and it is not either of the operations that RFC 3961
   implies for DES random-to-key.)  The key generation seed length for
   all three DES enctypes (des-cbc-md5, des-cbc-md4, and des-cbc-crc)
   is 7 bytes.
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From: Sam Hartman <[email-masked]>
Date: Thu, 07 Oct 2010 20:42:07 -0400

I believe the following is very good text for the preauth framework.  If
I can get an ACK from Jeff I'll run it by the IESG and if we don't get
problems there then send it into the rfc editor.  Note that we'll need
an explicit ACK from Tim before publication.