Subject: Comment on RFC 3161/3161bis

From: [email-masked] (Peter Gutmann)
Date: Fri, 17 Jan 2003 20:30:40 +1300

Appendix A contains some text on using timestamps with CMS ("a sensible way
of...").  Although this quacks like a CMS Countersignature, it is in fact
different, both in the format and in the way it's generated.  The overall
format can't easily be fixed without changing the whole TSA response format,
but the way of generating the not-quite-countersignature is just gratuitously
incompatible.  CMS says:

 3.  The input to the message-digesting process is the contents
     octets of the DER encoding of the signatureValue field of the
     SignerInfo value with which the attribute is associated.

In contrast TSP says:

   The value of messageImprint field within TimeStampToken shall be a
   hash of the value of signature field within SignerInfo for the
   signedData being time-stamped.

In order to fix this, I would suggest the following change to 3161bis, to
follow the existing "CHANGE N-x" list:

-- Snip --

CHANGE N-7:

In Appendix A, removed the unfounded claim that what this RFC requires is
sensible, and added a warning about incompatibilities with the standard CMS
way of doing things.

-- Snip --

Peter.