EvictControl get key handle

[andriy-fd]

Hello,

Are there any ability to get handle of the object that was made persistent.

consider next case:

1. create primary key
2. EvictControl it so that it is made persistent

next time application starts, it does:

1. check if there is already key stored at specific handle
2. use the key to sign data

first part I have done:

TPMT_PUBLIC primTempl(TPM_ALG_ID::SHA256,
		TPMA_OBJECT::sign 
		| TPMA_OBJECT::userWithAuth
		| TPMA_OBJECT::fixedParent 
		| TPMA_OBJECT::fixedTPM 
		| TPMA_OBJECT::sensitiveDataOrigin,
		null,
		TPMS_RSA_PARMS(null, TPMS_SCHEME_RSASSA(TPM_ALG_ID::SHA256), 2048, 0),
		TPM2B_PUBLIC_KEY_RSA());

auto storagePrimary = tpm.CreatePrimary(TPM_RH::OWNER, null, primTempl, null, null);

// put the primary key into NV with EvictControl
TPM_HANDLE persistentHandle = TPM_HANDLE::Persistent(5);

tpm.EvictControl(TPM_RH::OWNER, storagePrimary.handle, persistentHandle);

how would I check that the key is there and get it's handle vs creating key each time?

[andriy-fd]

After thinking more this seems to be silly question, just in case someone else faces with the same - there is an ability to use handle directly, e.g.

// define a handle
TPM_HANDLE persistentHandle = TPM_HANDLE::Persistent(5);

// use it for e.g. signing
auto sig = tpm.Sign(persistentHandle, dataToSign, TPMS_SIG_SCHEME_RSASSA(TPM_ALG_ID::SHA256), null);

there is still one problem though, the handle might not be valid. I mean - there might be no key stored at that handle. The was how I check that, is try to load public data from that handle... if that fails - no key.

try
{
	// Attempt to read the public part of the key
	auto publicPart = tpm.ReadPublic(persistentHandle);
}
catch (const exception& e)
{
...
}

probably not the best approach, but at least something for now. Still thinking on something better.