OCSP question

[Stephen Wilson <swilson@lockstep.com.au>]

I have a question specifically about how to check the validity of an old
certificate at the time a given digital signature was created. 

My understanding of OCSP is that it returns the validity of a given
certificate at the time of the request (i.e. "now").  But what if I have a
old digitally signed transaction which I am trying to validate?  It could
have been signed years ago, or just days ago, the problem is the same.  The
"Relying Party" wants to know if the signer's certificate was valid at the
time of the signature (regardless of whether the certificate happens to
have subsequently expired or even revoked).  

Is the only way to validate old certificates to obtain the CRLs and delta
CRLs leading up to the time of the signature and reconstruct the
certificate validity? 

Or is there an OCSP variant that helps?  One that has the time-and-date of
interest as a parameter in the status check request?  

Or finally ... apart from the ill-fated VA model, are there any services on
the market today which provide this information easily?  

Cheers, 


Stephen Wilson
Lockstep Consulting Pty Ltd
www.lockstep.com.au
ABN 59 593 754 482

11 Minnesota Ave
Five Dock NSW 2046
Australia

P +61 (0)414 488 851

--------------------

About Lockstep 
Lockstep was established in early 2004 by noted authentication expert
Stephen Wilson, to provide independent advice and analysis on cyber
security policy, strategy, risk management, and identity management. 
Lockstep is also developing unique new smartcard solutions to address
privacy and identity theft.