Proposal: Support p256 signature algorithm for identity and event verification to be compatible with cloud KMS, HSM

[anhthii]

Overview:

To improve integration with external Key Management Services (KMS) that only support P-256 (NIST curve secp256r1), we propose extending mpcium's identity and event verification logic to support p256 in addition to the current default ed25519.

---

1. Signature Algorithm Selection

• Support two signature algorithms:

  • ed25519 (default)
  • p256 (NIST secp256r1, ECDSA)

• New CLI flag for generate-initiator

  --algorithm [ed25519|p256]   # default: ed25519

• If --algorithm is not provided, default to ed25519.

---

2. Public Key Input for P-256

mpcium

• If --algorithm=p256, require:

  --pubkey path/to/pubkey.pem

• PEM file must contain a valid ECDSA P-256 public key.

• The private key is never used or required.

• For ed25519, the keypair continues to be generated internally.

---

3. Event initiator identity File Format

Update the identity file to include:

{
  "algorithm": "p256",
  "public_key": "<base64-encoded DER or hex string>",
  ...
}

• algorithm must always be present.
• public_key must be stored regardless of algorithm source.

---

---

5. Signature Verification Logic

Update the signature verification logic:

func (store *identityStore) VerifyInitiatorMessage(msg InitiatorMessage) error {
    algorithm := msg.Algorithm() // New method
    switch algorithm {
    case "ed25519":
        return store.verifyEd25519Message(msg)
    case "p256":
        return store.verifyP256Message(msg)
    default:
        return fmt.Errorf("unsupported signature algorithm: %s", algorithm)
    }
}

---

6. verifyP256Message Implementation

• Use crypto/ecdsa with elliptic.P256() and sha256 hash.
• Load public key from message or identity.
• Verify the ECDSA signature against the SHA-256 hash of the message.
• Normalize public key to a consistent format (e.g., from PEM or base64).

---

7. Node Configuration Support

Allow static configuration in config.yaml:

event_initiator_algorithm: "p256"  # or "ed25519", default: ed25519
event_initiator_pubkey: "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE..." # base64 DER

---

8. Backward Compatibility

• If algorithm is not defined:
  • Assume ed25519 for identity generation and verification.
• No changes required for existing ed25519 identities or initiators.

[tuananhk13bk]

I'm taking this one

[anhthii]

cool, thanks!