Re: Why is privateKeyUsagePeriod deprecated?

["Gregory S. Chudov" <chudov@xxxxxxxxxxxx>]

Greetings.

David Cooper wrote
> It is my understanding that use of this extension was deprecated since,
> unless signed messages are timestamped by a trusted time stamping
> service, there is no way of determining when a message was signed.
Yes, it is true, this extension does not help validating signatures.
But it has a different meaning. It expresses the policy, under which this
key
is used.

> >The tendency with X.509 has been to record as much of the policy as
possible
> >and that is automatically checkable in the cert. So this argues for
keeping
> >and using the private key usage period
>
> Exactly.  If you've got different validity periods for the public and
private
> portions of the key, then you really need to state it in the cert, even if
> only as an expression of CA policy on the topic.
>
> Peter.
Agree. And it's not only an expression of CA policy, this also
gives clients a way to verify that CA (or any other authority)
really follows it's own policy.

For example, Russian cryptographic practice dictates that
the private key MUST be destroyed before it expires.
If it is not destroyed, than it's considered compromised,
and the corresponding certificate should be revoked.
It's sad, that PKIXCMP doesn't define a key destruction announce message.
But of course, there's that GeneralMessage, that can be used for that...

So, privateKeyUsage states:
"I promise to destroy my key before given time. If i don't, consider it
compromized."
And the peer can verify this, e.g. by fetching key destruction announces, or
using some out-of-band mechanism.

Good luck,
Greg Chudov