sha2::Sha256, aes::Aes128 here codes for EKHash and EkCipher.
Those should be read from the template of the EK ideally.

Although in reality, the template would have been dropped already and we're only working with a PEM encoded public key, and there should be some kind of default value.
https://github.com/tpm2-software/tpm2-tools/blob/master/tools/tpm2_makecredential.c#L340

Anyone with an opinion?

Is your question about this test in particular, or about the interface of make_credential_ecc, and whether we can deduce the type params from the inputs?

I think generally you should be able to deduce the hash and the cipher for the EK if you know the nature of the public key, for example by doing the reverse of the mapping done here: https://github.com/parallaxsecond/rust-tss-esapi/blob/main/tss-esapi/src/abstraction/ek.rs

No that was an API question.

I know how to get the parameters from a Public, but I don't expect the public or its template to always available.

Is your question about this test in particular, or about the interface of make_credential_ecc, and whether we can deduce the type params from the inputs?

I think generally you should be able to deduce the hash and the cipher for the EK if you know the nature of the public key, for example by doing the reverse of the mapping done here: https://github.com/parallaxsecond/rust-tss-esapi/blob/main/tss-esapi/src/abstraction/ek.rs