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Re: [Jeffrey Hutzelman] LAST CALL - Public Key Cryptography for Initial Authentication in Kerberos



Sam,

Just because I find your response strange I'd like to add some reamrks.
Why do you mention PKIX here. Tom didn't mention it at all.
You could as well have mentioned SMIME.
Anyway, not too important.

Saying that kerberos has other rules than PKIX has nothing to
do with the problem. besides that PKIX has no rules and continue
s to use obsolete ASN.1, thus it may be good to use something else,
i.e. to ignore whatever some PKIX authors are proposing. :-)

There are two issues in Tom's message: The tagging with
context tags almost always explicit, and the wrapping.

Tagging is a matter of ket's say "taste", in fact, it is a matter of implementation
experience. ASN.1 after many years has come with AUTOMATIC tags
allowing automatically unambiguous and non-excessive explicit tagging.

The actual tagging appeared in the 03 draft in 1997 as far as I see.
The krb-wg first meeting was in Jul 2000 but the text was obviously
discussed before in cat. well, let's see the mail archives of this group.
oops. It is difficult to determine now what has "always" been discussed.

Wrapping: Strong boundaries would make sense if you don't have to
cross them

Interoperability note: Some implementations may not be able to decode
  wrapped CMS objects encoded with BER but not DER; specifically, they
may not be able to decode infinite length encodings.


something that seems to be necessary according to the previous citation.

As soon as you have the data structure that you wrap,
you can also encode them in DER. I doubt that you just have the
octet string contents only available as blobs.

I refer to the minutes of San Diego concerning the use of DER/BER
and wrapping. Must have been real fun, this meeting
The argument of the difficulties of parsing BER (in particular
when it is totally unrestricted) seem right to me, or better, that
it is too complex to mandate a BER parser.


There may be good arguments after years to keep the syntax or the bits
on the wire but it has been change just a year ago after 8 years or so.

Have fun
Peter



   Tom>         If it isn't too late to fix this without breaking
   Tom> lots of implementations, the ASN.1 in this specification is
   Tom> over-tagged.  In section 3.2.1, all three of the tags in
   Tom> PA-PK-AS-REQ are unnecessary, and the one on signedAuthPack
   Tom> is actually slightly harmful.  None of the tags in
   Tom> PKAuthenticator do any good either.  The OCTET STRING
   Tom> wrappings for subjectName and issuerAndSerialNumber are not
   Tom> really appropriate, and subjectName doesn't need a tag.  Even
   Tom> in AuthPack, pkAuthenticator and clientDHNonce don't need
   Tom> tags.  Similarly, in 3.2.3, there is no reason for any of the
   Tom> tags in PA-PK-AS-REP, DHRepInfo, or KDCDHKeyInfo.  The tags
   Tom> in ReplyKeyPack in 3.2.3.2 also seem unnecessary.

The kerberos working group has a rather different philosophy on ASN.1
than the PKIX community.  We've attempted to draw strong boundaries
around structures to the extent that we can: kerberos structures use
our conventions; PKIX structures use yours.

The short answer is that tagging issues have been discussed
extensively across all our ASN.1 usage.





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