Re: [pkix] Private key usage period extension clarification

"Erik Andersen" <> Tue, 10 May 2016 07:30 UTC

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From: "Erik Andersen" <>
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Date: Tue, 10 May 2016 09:30:48 +0200
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Subject: Re: [pkix] Private key usage period extension clarification
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Hi Denis,


Thanks for your comments. I agree with your proposed NOTE 2. However, this
note should not give the impression that it reflects the semantic for the
extension. There are other usages of this extension as described in document
( Stefan
also had some other example. You gave yourself also another example, so I
still like to include my proposed note i addition.






Fra: Denis [] 
Sendt: 09 May 2016 10:13
Til: Erik Andersen <>eu>; Directory list
<>rg>; PKIX <>
Emne: Re: [pkix] Private key usage period extension clarification



I agree with the change proposals up to NOTE 1. However, I do not agree with
the current NOTE 2 which states:

NOTE 2 - If the verifier of a digital signature wants to check that the
certificate has not been revoked, for example, 
due to key compromise, up to the time of verification, then a valid
certificate will still exist for the public key at verification time.
After the certificate(s) for a public key have expired, a signature verifier
cannot rely on compromises being notified via CRLs.

Erik's comment is: "It is difficult to tell what that note wants to say that
is particular to this extension. Maybe the writer had some undocumented
semantic in mind".

I agree that the note is far from being crystal clear, but it is dealing
with the verification of a digital signature before and after the expiry of
the certificate. 

Denis's comment is:

"Note 2 is trying to explain the verification of a digital signature before
and after the expiry of the certificate. 
This has nothing to do with the private key usage period extension and thus
it should be deleted".

However, I would propose to replace it with a useful clarification.

Replace NOTE 2 of with:

The period of use of the private key corresponding to a public key can only
be enforced if both the private key and the corresponding certificate 
are placed in a tamper resistant hardware module that contains a reliable
clock synchronized with UTC. When this is not the case, it can help 
a signer to avoid to use a signing private key up to the very end of the
validity period of the certificate.