Subject: Re: Online Certificate Revocation Protocol

From: [email-masked] (Peter Gutmann)
Date: Thu, 14 Jun 2001 11:13:07 (NZST)

Massimiliano Pala <[email-masked]> writes:
>Peter Gutmann wrote:
>>There's another revocation status which needs a way of indicating it which is
>>somewhat trickier, I'll bring it up here in case anyone has any ideas:
>>Sometimes a cert can be issued in error, what's needed here is a revocation
>>reason which says that not only is the cert revoked, it should never be and
>>was never valid at any time for any reason.  You can sort of achieve this by
>
>In this case, when will br the entry removed from the CRL ? When the 
>certificate will be expired ?? Or should it be left in all future CRLs ?
 
Well, CMP leaves pretty much everything to CA policy so it's up to the 
individual CA.  I leave it in the CRL until the cert expires anyway, but 
that's just me (I'm also currently overloading the "undefined" reason code in 
the hope that, since you're not supposed to use it, it's a spare code which 
can be used to mean "never valid", but it really needs its own reason code to 
indicate the true status).
 
Peter.

---

From: "Liaquat Khan" <[email-masked]>
Date: Thu, 14 Jun 2001 14:18:55 +0100

I agree a new reason code of ("never valid") has uses.  This will allow a
relying party when verifying a digital signatures using a certificate, which
when performing revocation checking is found to be on a CRL with the a new
reason code ("never valid"), to detect that the digital signature should not
be trusted even if the digital signature was produced before the time of the
revocation of the certificate.   Otherwise in theory signature produced
before the revocation will continue to be considered valid - not a good
situation for the relying party or for the CA.

However, I cannot see the need to keep such a certificate on a CRL even
after it has expired...what does this achieve?

Regards,
Liaquat

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On
Behalf Of Peter Gutmann
Sent: 14 June 2001 11:13
To: [email-masked]; [email-masked]
Subject: Re: Online Certificate Revocation Protocol

Well, CMP leaves pretty much everything to CA policy so it's up to the
individual CA.  I leave it in the CRL until the cert expires anyway, but
that's just me (I'm also currently overloading the "undefined" reason code
in
the hope that, since you're not supposed to use it, it's a spare code which
can be used to mean "never valid", but it really needs its own reason code
to
indicate the true status).

Peter.

---

From: Denis Pinkas <[email-masked]>
Date: Mon, 18 Jun 2001 10:58:34 +0200

Liaquat,

> situation for the relying party or for the CA.

This is the reverse situation. If a signature was tested to be valid e.g. in
June 2000 and the certificate was revoked for any reason e.g. in May 2001,
then the signature tested good in June 2000, shall continue to be valid,
otherwise it would not be a good situation for relying parties.

Denis

---

From: "Liaquat Khan" <[email-masked]>
Date: Mon, 18 Jun 2001 12:56:54 +0100

I agree with what you are saying Denis, but the scenario I was painting was
slightly different.  Imagine a digital signature which is being verified for
the first time by a relying party.  The relying party checks the relevant
CRL and realises that the certificate is revoked.  However the signature was
produced before the revocation occurred.  It would be nice for the CA to
indicate in the CRL within the reason code that the certificate was never
valid.  So signatures performed even before the revocation should not be
trusted.

Regards,
Liaquat

-----Original Message-----
From: Denis Pinkas [mailto:[email-masked]]
Sent: 18 June 2001 09:59
To: [email-masked]
Cc: [email-masked]
Subject: Re: Online Certificate Revocation Protocol

Liaquat,

Denis

> >>There's another revocation status which needs a way of indicating it
which
> is
> >>was never valid at any time for any reason.  You can sort of achieve
this
> by

---

From: Denis Pinkas <[email-masked]>
Date: Mon, 18 Jun 2001 14:22:03 +0200

Liaquat,

> I agree with what you are saying Denis, 

Good.

> but the scenario I was painting was
> CRL and realises that the certificate is revoked.  

So the signature is invalid.

> However the signature was produced before the revocation occurred.  

How can a relying party know that the signature was produced before the
revocation occurred ? Unless a time-stamp has been applied it is hard to
prove. Then if you want to prove that the signature was valid (or invalid)
at the time the time-stamp was applied, then you must get the revocation
information available at that time.

> It would be nice for the CA to

One again, signatures performed before the revocation shall remain trusted.

Regards,

Denis