noise-js.ts

1/**2 * Noise NK initiator for Android / Capacitor.3 * Pattern: Noise_NK_25519_ChaChaPoly_BLAKE2s4 *5 * The native Rust host runs `snow` to drive the same pattern; this JS6 * implementation produces wire-identical bytes so a Capacitor WebView client7 * can connect to the desktop host over WebSocket.8 *9 * MUST stay in lockstep with the native side. The cross-check test in10 * `noise-js.test.ts` pins exact byte outputs against fixed inputs so a11 * regression on either side fails CI before any device pair gets wedged.12 */1314import { generateKeyPair, sharedKey } from "@stablelib/x25519";15import { ChaCha20Poly1305 } from "@stablelib/chacha20poly1305";16import { BLAKE2s } from "@stablelib/blake2s";17import { HKDF } from "@stablelib/hkdf";18import { SHA256 } from "@stablelib/sha256";19import { HMAC } from "@stablelib/hmac";2021const PROTOCOL_NAME = "Noise_NK_25519_ChaChaPoly_BLAKE2s";2223function initHash(): Uint8Array {24  const nameBytes = new TextEncoder().encode(PROTOCOL_NAME);25  if (nameBytes.length <= 32) {26    const h = new Uint8Array(32);27    h.set(nameBytes);28    return h;29  }30  const sha = new SHA256();31  sha.update(nameBytes);32  return sha.digest();33}3435function mixHash(h: Uint8Array, data: Uint8Array): Uint8Array {36  const blake = new BLAKE2s(32);37  blake.update(h);38  blake.update(data);39  return blake.digest();40}4142function hkdf2(ck: Uint8Array, ikm: Uint8Array): [Uint8Array, Uint8Array] {43  const out = new HKDF(SHA256, ikm, ck).expand(64);44  return [out.slice(0, 32), out.slice(32, 64)];45}4647export interface NoiseNKSession {48  encrypt(plaintext: Uint8Array): Uint8Array;49  decrypt(ciphertext: Uint8Array): Uint8Array;50  handshakeHash: Uint8Array;51}5253/**54 * Run the initiator side of the Noise NK handshake. The caller provides55 * `send` / `receive` for the two transport-side handshake messages and gets56 * back a session object that encrypts/decrypts subsequent transport frames.57 */58export async function noiseNKInitiator(59  responderStaticPublicKey: Uint8Array,60  send: (msg: Uint8Array) => Promise<void>,61  receive: () => Promise<Uint8Array>,62): Promise<NoiseNKSession> {63  let h: Uint8Array = initHash();64  let ck: Uint8Array = h.slice();6566  // NK pre-message: mix responder static public key.67  h = mixHash(h, responderStaticPublicKey);6869  const ephemeral = generateKeyPair();7071  // --- Message 1: e, es ---72  h = mixHash(h, ephemeral.publicKey);73  const es = sharedKey(ephemeral.secretKey, responderStaticPublicKey);74  const [ck1, k1] = hkdf2(ck, es);75  ck = ck1;7677  const cipher1 = new ChaCha20Poly1305(k1);78  const nonce1 = new Uint8Array(12);79  const encrypted1 = cipher1.seal(nonce1, new Uint8Array(0), h);80  h = mixHash(h, encrypted1);8182  const msg1 = new Uint8Array(32 + encrypted1.length);83  msg1.set(ephemeral.publicKey, 0);84  msg1.set(encrypted1, 32);85  await send(msg1);8687  // --- Message 2: e, ee ---88  const msg2 = await receive();89  if (msg2.length < 48) throw new Error("Noise NK: msg2 too short");9091  const remoteEphemeralPublic = msg2.slice(0, 32);92  const encrypted2 = msg2.slice(32);9394  h = mixHash(h, remoteEphemeralPublic);95  const ee = sharedKey(ephemeral.secretKey, remoteEphemeralPublic);96  const [ck2, k2] = hkdf2(ck, ee);97  ck = ck2;9899  const cipher2 = new ChaCha20Poly1305(k2);100  const nonce2 = new Uint8Array(12);101  const decrypted2 = cipher2.open(nonce2, encrypted2, h);102  if (!decrypted2) {103    throw new Error("Noise NK: msg2 auth failed — wrong responder key or MITM");104  }105  h = mixHash(h, encrypted2);106107  // --- Transport phase ---108  const [sendKey, recvKey] = hkdf2(ck, new Uint8Array(0));109  const handshakeHash = h.slice();110111  let sendNonce = 0n;112  let recvNonce = 0n;113114  function nonceBytes(n: bigint): Uint8Array {115    const buf = new Uint8Array(12);116    new DataView(buf.buffer).setBigUint64(4, n, true);117    return buf;118  }119120  const sendCipher = new ChaCha20Poly1305(sendKey);121  const recvCipher = new ChaCha20Poly1305(recvKey);122123  return {124    encrypt(plaintext) {125      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));126    },127    decrypt(ciphertext) {128      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));129      if (!result) throw new Error("Noise NK: decryption failed");130      return result;131    },132    handshakeHash,133  };134}135136/**137 * Compute the auth proof byte-for-byte identically to the native host.138 * See `native/peach-sync-host/src/auth.rs::proof_for`.139 *140 * proof = HMAC-SHA256(141 *   key   = X25519(local_priv, remote_pub),  // 32-byte DH shared142 *   data  = "peach-sync-v1-initiator-auth"143 *        || initiator_public144 *        || responder_public145 *        || nonce_32146 * )147 *148 * The initiator and responder both pass the same DH peer key (their PEER's149 * public key) and the same initiator_public/responder_public ordering so the150 * MAC matches. `mac_for` in auth.rs implements both directions; this helper151 * targets the initiator-side: `local_priv` is the initiator's private key,152 * `remote_pub` is the responder's public key.153 */154const AUTH_DOMAIN = new TextEncoder().encode("peach-sync-v1-initiator-auth");155156export function computeAuthProof(157  initiatorPrivate: Uint8Array,158  initiatorPublic: Uint8Array,159  responderPublic: Uint8Array,160  nonce: Uint8Array,161): Uint8Array {162  if (nonce.length !== 32) throw new Error("auth nonce must be 32 bytes");163164  const dh = sharedKey(initiatorPrivate, responderPublic);165  const mac = new HMAC(SHA256, dh);166  mac.update(AUTH_DOMAIN);167  mac.update(initiatorPublic);168  mac.update(responderPublic);169  mac.update(nonce);170  return mac.digest();171}172173interface AuthChallengeFrame {174  type: "CHALLENGE";175  nonce_hex: string;176  responder_public_key_hex: string;177}178179interface AuthProofFrame {180  type: "PROOF";181  initiator_public_key_hex: string;182  proof_hex: string;183}184185function bytesToHex(bytes: Uint8Array): string {186  return Array.from(bytes, (b) => b.toString(16).padStart(2, "0")).join("");187}188189function hexToBytes(hex: string): Uint8Array {190  if (hex.length % 2 !== 0) throw new Error("invalid hex");191  const bytes = new Uint8Array(hex.length / 2);192  for (let i = 0; i < hex.length; i += 2) {193    bytes[i / 2] = parseInt(hex.slice(i, i + 2), 16);194  }195  return bytes;196}197198/**199 * Drive the initiator side of the post-handshake challenge/proof round. The200 * responder sends a `Challenge` JSON frame; we compute the HMAC and reply201 * with a `Proof` frame. Both frames are encrypted via the post-handshake202 * Noise transport (caller owns the `sendEncrypted` / `receiveEncrypted` pair).203 */204export async function performInitiatorAuth(205  session: NoiseNKSession,206  ourPrivateKey: Uint8Array,207  ourPublicKey: Uint8Array,208  responderPublicKey: Uint8Array,209  sendEncryptedJson: (data: Uint8Array) => Promise<void>,210  receiveEncryptedJson: () => Promise<Uint8Array>,211): Promise<void> {212  void session; // hash bound into MAC via the DH key only — kept for future fields213214  const challengeBytes = await receiveEncryptedJson();215  const challenge = JSON.parse(new TextDecoder().decode(challengeBytes)) as AuthChallengeFrame;216  if (challenge.type !== "CHALLENGE") {217    throw new Error("expected CHALLENGE frame");218  }219  const nonce = hexToBytes(challenge.nonce_hex);220  const responderKeyFromChallenge = hexToBytes(challenge.responder_public_key_hex);221  // Defence against an off-key challenge: the responder's claimed key MUST be222  // the one we Noise-NK-handshook against, otherwise an active MITM that223  // managed to substitute a different key is rerouting the auth round.224  if (225    responderKeyFromChallenge.length !== responderPublicKey.length ||226    !responderKeyFromChallenge.every((b, i) => b === responderPublicKey[i])227  ) {228    throw new Error("responder key in challenge does not match Noise handshake");229  }230231  const proof = computeAuthProof(ourPrivateKey, ourPublicKey, responderPublicKey, nonce);232  const proofFrame: AuthProofFrame = {233    type: "PROOF",234    initiator_public_key_hex: bytesToHex(ourPublicKey),235    proof_hex: bytesToHex(proof),236  };237  await sendEncryptedJson(new TextEncoder().encode(JSON.stringify(proofFrame)));238}239240export { bytesToHex, hexToBytes };