ED25519 Fingerprint Generation

ed25519Fingerprint.js

const bs58 = require('bs58');

const MULTICODEC_ED25519_PUB_HEADER = new Uint8Array([ 0xed, 0x01 ]);
const MULTIBASE_BASE58BTC_HEADER = 'z';

const ed25519Fingerprint = ({
  base64PubKey,
}) => {
  const base64PubKeyBuffer = Buffer.from(base64PubKey, 'base64');
  const uint8PubKey = Uint8Array.from(base64PubKeyBuffer);
  const multibaseKey = new Uint8Array(MULTICODEC_ED25519_PUB_HEADER.length + uint8PubKey.length);
  multibaseKey.set(MULTICODEC_ED25519_PUB_HEADER);
  multibaseKey.set(uint8PubKey, MULTICODEC_ED25519_PUB_HEADER.length);
  const base58Fingerprint = MULTIBASE_BASE58BTC_HEADER + bs58.encode(multibaseKey);
  return base58Fingerprint;
};

// NOTE no padding in b64!
const base64PubKey = 'DA7IPk3KCWp4bRQ413wV57FZOTycSx2FF_uaI4zF28c';
const fingerprint = ed25519Fingerprint({
  base64PubKey,
});

console.log({
  fingerprint,
  did: `did:key:${fingerprint}`,
});