Add ctx.get_time

[nilsb99]

For a time-based remote attestation project in a uni class, we needed this function and wanted to contribute it to upstream.

We followed the existing implementation of ctx.quote() to write ctx.get_time() and its test.

[Superhepper]

Thank you so much for the PR. I had some comments.

[ionut-arm]

Awesome, thanks for the patch, it looks pretty good! Amazing that you've worked with something like this in Uni :)

[ionut-arm]

I think these two are actually required, the first one for the endorsement, the second for the signing key. Looking at quote above I wonder if that's a bug, AFAICT the spec asks for one authorization session at least there.

[Superhepper]

TCG TSS 2.0 Enhanced System API (ESAPI) Specification, Version 1.00, Revision 14, October 1, 2021

11.3.45 Esys_GetTime Functions
TSS2_DLL_EXPORT TSS2_RC Esys_GetTime_Async(
ESYS_CONTEXT *esysContext,
ESYS_TR privacyAdminHandle,
ESYS_TR signHandle,
ESYS_TR privacyAdminHandleSession1,
ESYS_TR signHandleSession2,
ESYS_TR optionalSession3,
TPM2B_DATA const *qualifyingData,
TPMT_SIG_SCHEME const *inScheme);

I think you are right only the third session is optional.

[Superhepper]

Regarding Esys_Quote.

TCG TSS 2.0 Enhanced System API (ESAPI) Specification, Version 1.00, Revision 14, October 1, 2021

11.3.42 Esys_Quote Functions
TSS2_DLL_EXPORT TSS2_RC Esys_Quote_Async(
ESYS_CONTEXT *esysContext,
ESYS_TR signHandle,
ESYS_TR signHandleSession1,
ESYS_TR optionalSession2,
ESYS_TR optionalSession3,
TPM2B_DATA const *qualifyingData,
TPMT_SIG_SCHEME const *inScheme,
TPML_PCR_SELECTION const *PCRselect);

So it seems Quote is wrong as well because the first session should be required.

[Superhepper]

@nilsb99 I did not ask this before. But do you need this in an official release? Because if you do I suggest you cherry-pick this to the 7.x.y branch in a new PR.

[ionut-arm]

🚀