RE: Time-Stamp: Why not use several hashes?

[Robert Zuccherato <robert.zuccherato@xxxxxxxxxxx>]

Manuel;

This is presently supported.  Since a MessageImprint is a hashAlgorithm
(AlgorithmIdentifier) followed by the hashedMessage (an OCTET STRING) all
you have to do is define an AlgorithmIdentifier which means "the SHA-1 hash
concatenated with the MD5 hash" for example and then include the SHA-1 hash
of the message concatenated with the MD5 hash in the hashedMessage field.

	Robert.

> ----------
> From: 	Manuel Heras Gilsanz[SMTP:mherasg@nexo.es]
> Sent: 	Thursday, April 08, 1999 4:45 PM
> To: 	ietf-pkix@imc.org; afd@fnmt.es
> Subject: 	Time-Stamp: Why not use several hashes?
> 
> Hi.
> 
> In the (now expired) latest PKIX draft on time-stamping protocols from
> Sept. 23, 1998, time-stamp requests and tokens support the insertion of
> a single message imprint.
> 
> I think several message imprints should be supported. If a hash
> algorithm were broken, time-stamp tokens using it (as the single message
> imprint) would have to be regarded invalid (even if some kind of linking
> mechanism were implemented!). If several hashes had been used, the token
> would still be valid, and it could be promptly renewed in order to
> prevent invalidation should further advances in cryptography render
> other hashes obsolete!
> 
> (One must be careful here: there are different extents to which a hash
> algorithm could be broken; in Appendix A of  PKITS-D3
> [http://www.fnmt.es/pkits] there is an interesting analysis of the
> implications that the different kinds of hash failures would have on the
> time-stamping process.)
> 
> Of course the requirements on the time-stamp verification process would
> also have be modified to require ("MUST" level) *all* the hashes to
> correctly verify in order to regard the corresponding time-stamp token
> valid.
> 
> Best regards,
> 
>     - Manuel -
> 
> ----
> Manuel Heras-Gilsanz (mherasg@nexo.es)
> Independent Security Consultant
> Phone: +34-629 07 53 31
>