signed verification response

[Trevor Perrin <trevp@trevp.net>]

John Messing raised an interesting idea, offlist:

Perhaps, when calling DSS Verify, the client could request that the service 
sign its response.  Then the client could archive the response, and if the 
client was later accused of mistakenly relying on a false signature, or 
processing the signature contents incorrectly, the client could produce the 
signed response and claim "don't blame me, blame the DSS service".

Or the client could attach the response as an unsigned attribute to the 
signature, and pass them both along to a 3rd party, in which case this 
would be yet another way for A to present 3rd-party evidence of a 
signature's validity to B (along with counter-signing, and the EPM approach 
of using a time-stamp, and the approach of adding cert-path validity info, 
like signed OCSP responses).

Anyways, we could add a "Whether response should be signed" option in 
3.6.2., if people support this.

Trevor