Code assumes using ECDSA P-384 / SHA-384

Per ### TDX Migration TD Design Guide Rev 0.9.3 (2025-08-21)

> Table 7-1: MigTD cryptography algorithm
>
> | cryptography | **options** | **recommendation** |
> |-------------------|----------------------------|--------------------|
> | digital signature | **rsa, ecdsa** | ecdsa-nist_p384 |
> | key exchange | ecdhe | ecdhe-secp384r1 |
> | aead | aes-gcm, chacha20-poly1305 | aes-256-gcm |

For "digital signature", the permitted **options** are RSA and ECDSA; P-384
is only the recommendation

However code already hard-force ECDSA P-384 / SHA-384 even though the spec
allows more options.

`verify_signature()` in [src/migtd/src/ratls/server_client.rs](../src/migtd/src/ratls/server_client.rs#L1056):

```rust
fn verify_signature(cert: &Certificate, verified_report: &[u8]) -> CryptoResult<()> {
let public_key = cert
.tbs_certificate
.subject_public_key_info
.subject_public_key
.as_bytes()
.ok_or_else(|| CryptoError::ParseCertificate)?;
let tbs = cert.tbs_certificate.to_der()?;
let signature = cert.signature_value.as_bytes().ok_or_else(|| CryptoError::ParseCertificate)?;
verify_public_key(verified_report, public_key)?;
ecdsa_verify(public_key, &tbs, signature) // <-- P-384 only
}
```

`ecdsa_verify` is hard-wired to `ECDSA_P384_SHA384_ASN1` in
[src/crypto/src/rustls_impl/ecdsa.rs](../src/crypto/src/rustls_impl/ecdsa.rs#L91):

```rust
pub fn ecdsa_verify(public_key: &[u8], data: &[u8], signature: &[u8]) -> Result<()> {
let pk = UnparsedPublicKey::new(&signature::ECDSA_P384_SHA384_ASN1, public_key);
pk.verify(data, signature).map_err(|_e| Error::EcdsaVerify)
}
```

`verify_signature_with_algorithm()` in [src/crypto/src/lib.rs](../src/crypto/src/lib.rs#L236):

```rust
// ECDSA with SHA-384: 1.2.840.10045.4.3.3
const ECDSA_WITH_SHA384: &[u32] = &[1, 2, 840, 10045, 4, 3, 3];

// Only ECDSA-P384 with SHA384 signature is supported
match oid_arcs.as_slice() {
ECDSA_WITH_SHA384 => ecdsa::ecdsa_verify_with_algorithm(
public_key,
message,
signature,
&ecdsa::ECDSA_P384_SHA384_ASN1,
)
.map_err(|_| Error::SignatureVerification),
_ => {
// Unsupported algorithm
Err(Error::UnsupportedAlgorithm)
}
}
```

`EcdsaPk::new()` in [src/crypto/src/rustls_impl/ecdsa.rs](../src/crypto/src/rustls_impl/ecdsa.rs#L31):

```rust
pub fn new() -> Result {
let rand = SystemRandom::new();
EcdsaKeyPair::generate_pkcs8(&signature::ECDSA_P384_SHA384_ASN1_SIGNING, &rand)
.map(|pk| Self { pk })
.map_err(|_| Error::GenerateKeyPair)
}
```

Requester in [src/migtd/src/spdm/spdm_req.rs](../src/migtd/src/spdm/spdm_req.rs#L58) and
responder in [src/migtd/src/spdm/spdm_rsp.rs](../src/migtd/src/spdm/spdm_rsp.rs#L102):

```rust
let config_info = common::SpdmConfigInfo {
// ...
base_asym_algo: SpdmBaseAsymAlgo::TPM_ALG_ECDSA_ECC_NIST_P384,
base_hash_algo: SpdmBaseHashAlgo::TPM_ALG_SHA_384,
dhe_algo: SpdmDheAlgo::SECP_384_R1,
aead_algo: SpdmAeadAlgo::AES_256_GCM,
req_asym_algo: SpdmReqAsymAlgo::TPM_ALG_ECDSA_ECC_NIST_P384,
// ...
};
```

Start by tracing algorithm selection and verification through src/migtd/src/ratls/server_client.rs, src/crypto/src/rustls_impl/ecdsa.rs, src/crypto/src/lib.rs, and the SPDM configuration in src/migtd/src/spdm/spdm_req.rs and spdm_rsp.rs. Determine how the permitted RSA and ECDSA options should be represented and negotiated without assuming P-384/SHA-384. Done means the relevant verification, key generation, and SPDM configuration paths support the intended spec-compliant options.

Written by the indexing model from the issue text.