Thank you very much, Hal, for the answers. The code at privaca website is
certainly going to be useful for me.
Regards,
Amruta
On Wed, Jan 20, 2010 at 2:04 PM, Hal Finney <[email protected]> wrote:
> Hi Amruta - answers inline:
>
> On Sun, Jan 17, 2010 at 3:07 PM, Amruta Gokhale
> <[email protected]> wrote:
> > Thank you for pointing me to a very useful description about the
> > verification of quote
> > operation.
> >
> > I am sorry about asking doubts on an old thread, but I still have two
> > questions:
> >
> > 1) The verifier should have the RSA public signing key for verifying the
> > signature
> > over the rgbData buffer. So is it okay if the prover(or the attesting
> party)
> > sends the
> > public key to the verifier? Will this be in accordance with the IMA
> > protocol?
> > Since the prover creates a new key pair each time via
> Tspi_Key_CreateKey(),
> > I suppose the only way for the verifier to know this public key is by
> > receiving it from
> > the prover. Or is there another way?
>
> I think generally you are right, the prover will generate the RSA
> signing key and will distribute it. He may send it directly to the
> verifier or he may publish it in some form, to make it available to
> other verifiers for example. It depends on how many provers and
> verifiers you would envision in the system.
>
> > 2) It follows from (1) above that there should be a central authority(CA)
> to
> > verify the key.
> > The communication with the CA would incur more work, both for the prover
> and
> > verifier.
> > Is there an efficient way than this to implement?
>
> Yes, the TCG assumes that AIKs suitable for issuing Quote operations
> would be verified by a CA which they call a Privacy CA. TPMs implement
> a protocol that lets a CA verify that a particular key is controlled
> by a TPM. This protocol allows the Privacy CA to issue a certificate
> on the AIK certifying that it is a valid TPM key.
>
> It is true that this may incur more work. However if the key is used
> many times, perhaps by many verifiers, it can be more efficient to
> just have the key checked once using the TPM protocol (which is rather
> complicated). As long as everyone trusts the Privacy CA then it is
> quick and easy to verify the certificates it issues and know that the
> Quote signing key is a valid TPM key.
>
> It is also possible for verifiers and signers to run the TPM protocol
> directly between themselves, in order to prove that the AIK is a real
> TPM key. This way no one has to trust the Privacy CA.
>
> I wrote some code to illustrate these two possibilities which is
> available from http://www.privacyca.com/code.html .
>
> Hal Finney
>
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