Re: [openpgp] Fingerprint schemes versus what to fingerprint

["Derek Atkins" <[e-mail]>]

Hi,

On Mon, April 11, 2016 11:41 am, Peter Gutmann wrote:
> Derek Atkins <[e-mail]> writes:
>
>>3) You have a smart card with raw key material and want to see which
>>   OpenPGP keys are there.
>
> That's PKCS #11, which means pretty much all crypto hardware that uses a
> standardised interface.

Are you expecting this would work in a vacuum?  I.e., would you expect
that you can take your OpenPGP smart card to a fresh system on which
you've never used OpenPGP ever and be able to plug in that smart card and
have it be able to sign a document?

If the answer is "no", then you're fine.  You can have private key lookup
metadata on the OpenPGP system online that gives you the handle to the
PKCS11 key.

If the answer is "yes", then the follow up question is whether there are
additional data available (e.g. storing associated public keys/certs) that
you could use to provide the additional metadata.  But I only see this
being an issue where you want to make a signature (which needs to know
your keyID) using a smartcard on a system that does not contain any
additional metadata.

Is this a real use case?

>>*) Other use cases???
>
> You have keys stored in a non-PGP format.  It makes keys from anywhere
> else
> pretty much unusable for PGP because you can't look them up.

It depends.  If I've got an X509 cert I can convert that to an OpenPGP
cert, and all the appropriate metadata is there.

I admit I'm not familiar enough with PKCS12 to know what data is included
there, or whether there is enough information in an X509 private key data
file to stand on its own.

>>It means that if someone reuses the key material then you cannot
>>differentiate the original from the subsequent certificate.
>
> That assumes you re-use the same key over and over, rather than just
> generating a fresh key when you need one.  That's X.509 practice, not PGP.
>
> Peter.

Yes, it does assume that.

This goes back to my arguments that we should include expiration time in
the key identifier/fingerprint so that there is a hard expiration.  In
order to change that you could copy the key material but it would
necessarily be a new "key" (certificate) because changing the expiration
would change the keyID/fingerprint.

-derek

-- 
       Derek Atkins                 617-623-3745
       [e-mail]             www.ihtfp.com
       Computer and Internet Security Consultant