openssl cms verification date

[Jochen Bern]

On 08.02.24 16:27, openssl-users-request at openssl.org digested:
> Date: Thu, 08 Feb 2024 15:46:54 +0100
> From: Tomas Mraz <tomas at openssl.org>
> 
> On Thu, 2024-02-08 at 14:13 +0100, Fran?ois Legal wrote:
>> Sure I get the point. You can't really be sure that the signature was
>> made at the clained time as the signerInfo structure is not signed
>> itself. Could you please comment however on why verifying the
>> validity of the certificate at the verification date is better in
>> that matter.
> 
> The expiration of the certificate means - albeit in an extreme case -
> that the private key is no longer trusted - i.e., it can do anything
> like malicious signatures of crafted data, etc. So unless you have
> trusted timestamps on the signed document, after the certificate
> expiration, the signature has no validity. Of course this is a little
> bit extreme view but...

Not that calling your official local lawmakers "extremists" will help 
you any ... ;-)

(I.e., when people like notaries keep hold of digitally signed documents 
for the required time of X years and the signature's validity ends 
before that, they're legally required to re-sign document and old 
signature(s) with a new signature of their own, which certifies that 
they had that data in their possession at a time when the old signature 
was still valid. Repeat as necessary for the *really* long-term archival.)

More generally speaking, what you'd *want* to do is to verify the 
signature WRT the moment you *yourself* obtained the doc+sig and can 
vouch that it hasn't been altered since - but that timestamp cannot be 
obtained by technical means (unless you habitually counter-sign right at 
*reception*) and "now" is used as a pessimistic approximation.

(... *usually* pessimistic. Had to pontificate on the pitfalls of not 
doing NTP or PTP properly just half an hour ago ...)

Kind regards,
-- 
Jochen Bern
Systemingenieur

Binect GmbH
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 3449 bytes
Desc: S/MIME Cryptographic Signature
URL: <https://mta.openssl.org/pipermail/openssl-users/attachments/20240208/1a1d6240/attachment.p7s>