openssl cms verification date

[Tomas Mraz]

I am sorry but I do not have any such document at hand.

Tomas

On Thu, 2024-02-08 at 16:15 +0100, Eliot Lear wrote:
> Tomas,
> 
> Having raised this point myself before, and having been corrected
> before 
> (and I'm glad I was), I wonder this: do you or other people on this
> list 
> have a favorite FAQy-like doc that talks about cert expiration and 
> verification strategies?  And not just expiration but Not-Valid-
> Before 
> as well.  There are real challenges with both, especially with IoT. 
> My 
> toe still hurts from having stubbed myself on this one repeatedly.
> 
> Thanks,
> 
> Eliot
> 
> On 08.02.2024 15:46, Tomas Mraz wrote:
> > On Thu, 2024-02-08 at 14:13 +0100, François Legal wrote:
> > > Le Jeudi, Février 08, 2024 11:46 CET, Tomas Mraz
> > > <tomas at openssl.org>
> > > a écrit:
> > >   
> > > > On Thu, 2024-02-08 at 11:37 +0100, François Legal wrote:
> > > > > Hello,
> > > > > 
> > > > > I'm new to this list.
> > > > > 
> > > > > I'm using pkcs7 packages to embbed firmware, to procide
> > > > > authenticity
> > > > > verification before doing firmware upgrades.
> > > > > 
> > > > > I use the openssl cms command for verification purpose, but
> > > > > face
> > > > > the
> > > > > following problem :
> > > > > when doing verify, openssl cms -verify does check whether the
> > > > > signing
> > > > > certificate is valid today, not whether or not it was still
> > > > > valid
> > > > > when the package got signed.
> > > > > 
> > > > > I saw the -attime option to specify the verification date,
> > > > > but
> > > > > found
> > > > > no easy way to fetch the signature date from the package for
> > > > > each
> > > > > signature.
> > > > > 
> > > > > So I was wondering if it was the intended function that the
> > > > > certificate validity verification was made at the
> > > > > verification
> > > > > date
> > > > > and not the signature date.
> > > > Yes, this was certainly intentional. I could envision that a
> > > > new
> > > > option
> > > > could be added to the cms command that would verify the
> > > > signature
> > > > at
> > > > the date when the signature was made. However please note that
> > > > without
> > > > some kind of assurance that the signature was really made at
> > > > the
> > > > time
> > > > that is recorded in the message, the signature could have been
> > > > done
> > > > with a key that was already expired anyway. This assurance is
> > > > done
> > > > usually by timestamping via a trusted timestamping authority
> > > > but
> > > > there
> > > > might be other means.
> > > > 
> > > 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...
> > 
> > > I already have a patch to provide for verifying the signature at
> > > signature time. Shall I send a pull request ?
> > Yes, sure. I assume you'll have to sign a CLA unless you already
> > did it
> > before.
> > 
> > > François
> > > 
> > > 
> > > > -- 
> > > > Tomáš Mráz, OpenSSL
> > > > 

-- 
Tomáš Mráz, OpenSSL