Subject: RE: howto combine a client signature with a timestamp?

From: Alicia da Conceicao <[email-masked]>
Date: Thu, 9 Sep 2004 07:38:02 -0400 (EDT)

Miguel A Rodriguez wrote:
> Take a look at RFC 3126, it extends CMS to include rfc3161 timestamps.

Hi Miguel:

I have looked in detail at RFC-3126, RFC-3161, & RFC-3369 and I am
still unclear how to generate a single complete example of my own CMS
"ES-T" (Electronic Signature with Timestamp).

I would be most greatly if ANYONE had ANY valid examples of a DER encoded
"ES-T", so that I can clarify exactly how it is done.  If anyone managed
to generate just a single example, please e-mail me the entire DER encoded
binary as an attachment, or inline as UUENCODE or BASE64.

On a side note, after giving it a lot of thought, I still think it would
be much better (and much more practical) to simply include a copy of a
client's original CMS signature as an unsigned/unauthenticated object
within the TSA's signerInfo, inside a RFC-3161 timestamp of that client's
signature.  So that the TSTInfo in the timestamp would contain a digest
hash of the client's digital signature, and one can independently
validate both the timestamp of the signature and the signature of the
original message, all from a single timestamp token.

I realize that this is backwards to the approach suggested in RFC-3126, in
that the orignal signature is appended to the timestamp token, instead of
appending the timestamp to the original signature.  But this approach has
a number of advantages.  One key advantage is for a TSA (TimeStamp
Authority) that must store timestamps for legacy clients, especially legacy
clients in banking that do not have the ability to properly store and
achive timestamps themselves for financial transactions.  By simply putting
the original client's digital signature within the timestamp that is
subsequently signed again by the TSA, the TSA can easily store both in a
single timestamp token with minimal effort, and that single token can be
used by a validator to validate both the original digital signature of a
message and the timestamp of that digital signature.

Comments???  Or has something similar already been proposed and is part
of an existing standard?

Thank you in advance.
Alicia.