Time-stamp issue

["Prashant Dambe" <[e-mail]>]

As specified in the draft-ietf-pkix-time-stamp-13.txt.
APPENDIX A - Signature Timestamp attribute using CMS
One of the major use of time stamping is to time stamp a digital signature to prove that the digital signature was created before 
a given time. Should the corresponding public key certificate be revoked this allows to know whether the signature was created before or after the revocation date.
A sensible place to store a time stamp is in a [CMS] structure as an unsigned attribute.

But what happens in the following scenario.
As timestamp token is placed as unsigned attribute, one of the possible attack is that 
if Time-stamp token it self is replaced with the Time-stamp token of the same signature value
inside CMS  i.e  If the same signature is time-stamped after some later time and Time-stamp in the 
original CMS is replaced,it not possibled to detect that orignal time-stamp has been replaced.
So putting time-stamp as unsigned attribute not works fine in all cases.

Thanks
Prashant Dambe.