Re: [Linux-ima-user] [TrouSerS-users] verifying quote using certificates

[adrian g. <adr...@gm...>]

hello hal, i was reading another thread about verifying the quote:
http://sourceforge.net/mailarchive/message.php?msg_id=4525A0BC.9000007%40ece.cmu.edu

with regards to this call:
Tspi_GetAttribData(hKey,
                       TSS_TSPATTRIB_RSAKEY_INFO,
                       TSS_TSPATTRIB_KEYINFO_RSA_MODULUS,

>                        &BlobLength, &BLOB);


&BlobLength is an unsigned int, and &BLOB a BYTE array.  Please correct me
if i'm wrong, BLOB would be a BIGNUM, and BlobLength the length of BLOB.
However, when i print out BlobLength, it seems too large (4131212846) for
BLOB.  and when i tried to verify if the exponent is 65537 by calling
GetAttribData with the flag TSS_TSPATTRIB_KEYINFO_RSA_EXPONENT instead, the
length of the BIGNUM is also very huge (134516825).

thanks - adrian


On Fri, Oct 10, 2008 at 3:08 AM, Hal Finney <hal...@gm...> wrote:

> Hi Adrian -
>
> One thing to keep in mind on Quote. For a Quote to be truly
> meaningful, the verifier needs to be confident that it is a TPM key -
> that is, that the private key is protected by the TPM and will never
> be readable outside the TPM. This basically means that it must be a
> non-migratable key, and it must have been generated on the TPM. Note,
> this is not enough by itself, there are a lot of other requirements
> that might have to be met, depending on the situation.
>
> I am not familiar with any openssl create_tpm_key() function. If it
> generates the key on the TPM, that might be suitable; but if it
> generates an off-chip key and then loads that onto the TPM, it would
> not be appropriate.
>
> For the other approach, generating a key on the TPM and then getting
> an X.509 certificate for it, keep in mind that an X.509 certificate is
> a rather inconvenient object for passing around keys. The only reason
> people use it is because it's what everyone uses. An X.509 cert does
> not just hold a key, it also has some kind of name or identity field,
> and further, it has a signature by (generally) some other key which
> binds the target key and target identity information. It's a very
> complex object. If all you want to do is to tell the other guy your
> public key, I'd probably suggest rolling your own format and just send
> the modulus in some form. But if you have to be X.509 compatible then
> you'll have to go through a lot of work.
>
> The first step (after generating the key) would be to read the key
> modulus using:
>
> Tspi_GetAttribData(hKey,
>                        TSS_TSPATTRIB_RSAKEY_INFO,
>                        TSS_TSPATTRIB_KEYINFO_RSA_MODULUS,
>                        &BlobLength, &BLOB);
>
> Once you have the modulus, you could insert it into an openssl RSA
> structure, and set the exponent field in that struct to 65537. From
> there, you will need to assemble an openssl X509 certificate
> structure, and then ultimately call the openssl X509_sign() function.
>
> Frankly, I don't understand how people manage to use openssl. There's
> no documentation for any of this stuff, that I can find! I always have
> to study the openssl source code to figure out how to use it, on those
> rare occasions when I am forced by circumstances to do so. Consider
> even something as mundane as creating an RSA key and creating a valid
> X.509 certificate to hold it. Forget about the TPM, just think about
> doing that step. The functionality exists in the openssl library to
> accomplish this, but I don't know of a single piece of documentation
> that tells how. (There do exist various HOWTOs across the web on how
> to do it from the openssl command line, but I haven't found anything
> about using the library.)
>
> Anyway, the bottom line is that generating the TPM key is easy.
> Creating X.509 certificates is hard. If you can figure out how to
> create X.509 certs, without involving the TPM, maybe with help from
> people on the openssl mailing lists, then it will be easy to modify
> that program to create the key on the TPM, copy the modulus field into
> whatever openssl structure needs it, and you're good to go.
>
> Hal
>
>
>
> On Wed, Oct 8, 2008 at 8:22 PM, adrian golding <adr...@gm...>
> wrote:
> > hello, with the Tspi_TPM_Quote01.c example and as a starting point, if i
> > want to let a remote party verify the quote, and i intend to send the
> > TSS_VALIDATION object as well as a certificate of my public key
> (self-signed
> > for now) over.  How do i either:
> > 1) create keys using openssl's create_tpm_key and load the key into my
> > quoting application before it signs the PCR?
> > or
> > 2) using the Tspi_Key_CreateKey function in  Tspi_TPM_Quote01.c to
> generate
> > the keys, and create a certificate with my public key so i could send it
> to
> > the remote party?
> > which way would be more encouraged?
> >
> > thanks - adrian
>