Subject: Re: Signing what you don't understand

From: [email-masked]
Date: Fri, 21 Jul 2000 15:35:38 -0400

Steve,

>>You are missing what I'm trying to say.  I'm not disputing that the
>>signature was created at the time claimed.
>>
>>The fact that CRLs include an invalidityDate field, which can indicate
that
>>a certificate was invalid well before that CRL was published means that
it
>>is possible for a certificate revocation to be "backdated" - i.e. even
>>though a perfectly valid CRL was referenced in the signature and
indicated
>>that the certificate was valid at the time the signature was constructed,
>>another CRL can be published (possibly much) later that will say the
>>certificate was invalid at the signing time.
>
>>
>>This renders signer-provided evidence of non-revocation of little use
>>(unless you are willing to let the signer-provided evidence of
>>non-revocation trump the more recent CRL that asserts that the
certificate
>>was invalid, which would open up a lot of security holes).
>
>The inclusion of the invalidity date in a CRL does not allow
>backdating, although it may appear that way.  The argument put forth
>to justify approval of this extension was to allow the CA to alert
>RPs to newly gained info re a revocation so that IF the RP had not
>acted upon a transaction (or the like) THEN the RP could elect to
>treat the signature as invalid.  However, if an RP has collected a
>CRL that covers the interval during which the transaction took place,
>then any later CRL with an invalidity date does not prevent the RP
>from using the CRL he acquired to support NR, i.e., the RP has
>exercised due diligence by obtaining the first CRL.

Note that I was talking about initial signature verification by the RP, not
subsequent NR.  The situation that I described had a signature with
embedded, signer-provided NR evidence which contained a CRL reference that
indicated one of the certificates was valid, but the RP obtains a more
recent CRL indicating that it has expired.  To decide whether to trust the
signature, the RP should use the most recent revocation data available to
him - the CRL that flags the certificate as revoked - and ignore the
earlier one referenced in the signature.

John

---

From: Stephen Kent <[email-masked]>
Date: Fri, 21 Jul 2000 16:13:56 -0400

John,

>earlier one referenced in the signature.

Under that circumstance, you're right.  Sorry I lost the context.

Steve