keys.ts

/**
 * Ed25519 key helpers and `did:key` derivation for the Verifiable OKF signer.
 *
 * Signing uses a 32-byte Ed25519 seed (private key). The signer never logs or
 * writes the private key; only the derived public key / DID and the signature
 * leave this module.
 */
import { ed25519 } from "@noble/curves/ed25519";
import { base58 } from "@scure/base";

/** multicodec prefix for an Ed25519 public key (0xed 0x01, varint). */
const ED25519_PUB_MULTICODEC = Uint8Array.from([0xed, 0x01]);

/** Public key (32 bytes) for an Ed25519 seed. */
export function publicKeyFromSeed(seed: Uint8Array): Uint8Array {
  return ed25519.getPublicKey(seed);
}

/** Detached Ed25519 signature (64 bytes) over `message`. Deterministic (RFC 8032). */
export function signEd25519(message: Uint8Array, seed: Uint8Array): Uint8Array {
  return ed25519.sign(message, seed);
}

/** Verify a detached Ed25519 signature. */
export function verifyEd25519(
  signature: Uint8Array,
  message: Uint8Array,
  publicKey: Uint8Array,
): boolean {
  return ed25519.verify(signature, message, publicKey);
}

/** `did:key` (multibase base58btc, multicodec ed25519-pub) for a public key. */
export function didKeyFromPublicKey(publicKey: Uint8Array): string {
  const bytes = new Uint8Array(ED25519_PUB_MULTICODEC.length + publicKey.length);
  bytes.set(ED25519_PUB_MULTICODEC, 0);
  bytes.set(publicKey, ED25519_PUB_MULTICODEC.length);
  return "did:key:z" + base58.encode(bytes); // multibase 'z' = base58btc
}

/** `did:key` for an Ed25519 seed. */
export function didKeyFromSeed(seed: Uint8Array): string {
  return didKeyFromPublicKey(publicKeyFromSeed(seed));
}