Keydata testsuite minor refactors and improvements and hashAlg

[sespiros]

This addresses:

• keyDataLegacyTestBase not used from [1/3] Keydata v3 platform API changes #265 (comment)
• use DecodeHexString from [1/3] Keydata v3 platform API changes #265 (comment)

Also makes hashAlg public as it will be used in a follow-up PR which will slightly rework the mockPlatformKeyDataHandler to use GCM and associated data to check expected values.

[chrisccoulson]

Thanks - this looks ok, although it does need a rebase on master now to resolve some merge conflicts.

I notice that xerrors.Errorf is replaced with fmt.Errorf in a few places - that's ok, but I think it's probably worth another PR to drop the xerrors dependency entirely given that we depend on go1.18 which has the required functionality in the standard library.

[chrisccoulson]

It might be worth just adding a note as to why this exists (it's just a crypto.Hash that can be serialed to JSON and DER)

[sespiros]

Thanks - this looks ok, although it does need a rebase on master now to resolve some merge conflicts.

Rebased on latest master.

I notice that xerrors.Errorf is replaced with fmt.Errorf in a few places - that's ok, but I think it's probably worth another PR to drop the xerrors dependency entirely given that we depend on go1.18 which has the required functionality in the standard library.

I did a cleanup for xerrors in secboot (that I will push in another PR) but it is still added as an indirect dependency. I can do the same for efilib (which also uses go 1.18). go-tpm2 also has it in its go.sum although it's not using it. Any reason why go-tpm2 is still in go 1.9?

[sespiros]

@chrisccoulson I also opened canonical/go-efilib#13

[chrisccoulson]

Thanks, this looks fine to me.