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 post-handshake auth proof.138 *139 * proof = HMAC-SHA256(140 *   key   = X25519(local_priv, remote_pub),  // 32-byte DH shared141 *   data  = "peach-sync-v1-initiator-auth"142 *        || initiator_public143 *        || responder_public144 *        || nonce_32145 * )146 *147 * Both sides pass the same DH peer key (their PEER's public key) and the same148 * initiator_public/responder_public ordering so the MAC matches. This helper149 * targets the initiator-side: `local_priv` is the initiator's private key,150 * `remote_pub` is the responder's public key.151 */152const AUTH_DOMAIN = new TextEncoder().encode("peach-sync-v1-initiator-auth");153154export function computeAuthProof(155  initiatorPrivate: Uint8Array,156  initiatorPublic: Uint8Array,157  responderPublic: Uint8Array,158  nonce: Uint8Array,159): Uint8Array {160  if (nonce.length !== 32) throw new Error("auth nonce must be 32 bytes");161162  const dh = sharedKey(initiatorPrivate, responderPublic);163  const mac = new HMAC(SHA256, dh);164  mac.update(AUTH_DOMAIN);165  mac.update(initiatorPublic);166  mac.update(responderPublic);167  mac.update(nonce);168  return mac.digest();169}170171interface AuthChallengeFrame {172  type: "CHALLENGE";173  nonce_hex: string;174  responder_public_key_hex: string;175}176177interface AuthProofFrame {178  type: "PROOF";179  initiator_public_key_hex: string;180  proof_hex: string;181}182183function bytesToHex(bytes: Uint8Array): string {184  return Array.from(bytes, (b) => b.toString(16).padStart(2, "0")).join("");185}186187function hexToBytes(hex: string): Uint8Array {188  if (hex.length % 2 !== 0) throw new Error("invalid hex");189  const bytes = new Uint8Array(hex.length / 2);190  for (let i = 0; i < hex.length; i += 2) {191    bytes[i / 2] = parseInt(hex.slice(i, i + 2), 16);192  }193  return bytes;194}195196/**197 * Drive the initiator side of the post-handshake challenge/proof round. The198 * responder sends a `Challenge` JSON frame; we compute the HMAC and reply199 * with a `Proof` frame. Both frames are encrypted via the post-handshake200 * Noise transport (caller owns the `sendEncrypted` / `receiveEncrypted` pair).201 */202/**203 * Run the responder side of the Noise NK handshake. Symmetric with204 * `noiseNKInitiator` — the caller provides `send` / `receive` for the two205 * handshake messages and gets back a session for transport-phase frames.206 *207 * Wire-identical with the Rust `snow` responder so an Android-as-host208 * pairing session can be driven by the desktop initiator and vice versa.209 */210export async function noiseNKResponder(211  ourStaticPrivateKey: Uint8Array,212  ourStaticPublicKey: Uint8Array,213  send: (msg: Uint8Array) => Promise<void>,214  receive: () => Promise<Uint8Array>,215): Promise<NoiseNKSession> {216  let h: Uint8Array = initHash();217  let ck: Uint8Array = h.slice();218219  // NK pre-message: mix our (responder) static public key. The initiator220  // pre-mixed the same key on its side; both transcripts must match.221  h = mixHash(h, ourStaticPublicKey);222223  // --- Message 1: e, es ---224  const msg1 = await receive();225  if (msg1.length < 48) throw new Error("Noise NK: msg1 too short");226  const remoteEphemeralPublic = msg1.slice(0, 32);227  const encrypted1 = msg1.slice(32);228229  h = mixHash(h, remoteEphemeralPublic);230  const es = sharedKey(ourStaticPrivateKey, remoteEphemeralPublic);231  const [ck1, k1] = hkdf2(ck, es);232  ck = ck1;233234  const cipher1 = new ChaCha20Poly1305(k1);235  const nonce1 = new Uint8Array(12);236  const decrypted1 = cipher1.open(nonce1, encrypted1, h);237  if (!decrypted1) {238    throw new Error("Noise NK: msg1 auth failed — wrong static key or MITM");239  }240  h = mixHash(h, encrypted1);241242  // --- Message 2: e, ee ---243  const ephemeral = generateKeyPair();244  h = mixHash(h, ephemeral.publicKey);245  const ee = sharedKey(ephemeral.secretKey, remoteEphemeralPublic);246  const [ck2, k2] = hkdf2(ck, ee);247  ck = ck2;248249  const cipher2 = new ChaCha20Poly1305(k2);250  const nonce2 = new Uint8Array(12);251  const encrypted2 = cipher2.seal(nonce2, new Uint8Array(0), h);252  h = mixHash(h, encrypted2);253254  const msg2 = new Uint8Array(32 + encrypted2.length);255  msg2.set(ephemeral.publicKey, 0);256  msg2.set(encrypted2, 32);257  await send(msg2);258259  // --- Transport phase ---260  // hkdf2 returns (k1, k2); the initiator uses k1 to send and k2 to receive,261  // so the responder swaps: k1 → recv, k2 → send.262  const [initiatorSendKey, responderSendKey] = hkdf2(ck, new Uint8Array(0));263  const handshakeHash = h.slice();264265  let sendNonce = 0n;266  let recvNonce = 0n;267268  function nonceBytes(n: bigint): Uint8Array {269    const buf = new Uint8Array(12);270    new DataView(buf.buffer).setBigUint64(4, n, true);271    return buf;272  }273274  const sendCipher = new ChaCha20Poly1305(responderSendKey);275  const recvCipher = new ChaCha20Poly1305(initiatorSendKey);276277  return {278    encrypt(plaintext) {279      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));280    },281    decrypt(ciphertext) {282      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));283      if (!result) throw new Error("Noise NK: decryption failed");284      return result;285    },286    handshakeHash,287  };288}289290/**291 * Constant-time 32-byte equality. The MAC comparison in `verifyAuthProof`292 * goes through this so a same-LAN attacker can't time the HMAC compare.293 */294function constantTimeEq(a: Uint8Array, b: Uint8Array): boolean {295  if (a.length !== b.length) return false;296  let diff = 0;297  for (let i = 0; i < a.length; i++) diff |= a[i]! ^ b[i]!;298  return diff === 0;299}300301/**302 * Drive the responder side of the post-handshake challenge/proof round. We303 * generate a random 32-byte nonce, send `Challenge`, receive `Proof`, and304 * verify. Returns the initiator's authenticated public key on success.305 *306 * The MAC key is X25519(our_priv, initiator_pub) and the data is the same307 * domain-separated transcript both sides feed into HMAC-SHA256.308 */309export async function performResponderAuth(310  session: NoiseNKSession,311  ourPrivateKey: Uint8Array,312  ourPublicKey: Uint8Array,313  sendEncryptedJson: (data: Uint8Array) => Promise<void>,314  receiveEncryptedJson: () => Promise<Uint8Array>,315): Promise<{ initiatorPublicKey: Uint8Array }> {316  void session;317318  const nonce = new Uint8Array(32);319  crypto.getRandomValues(nonce);320321  const challenge: AuthChallengeFrame = {322    type: "CHALLENGE",323    nonce_hex: bytesToHex(nonce),324    responder_public_key_hex: bytesToHex(ourPublicKey),325  };326  await sendEncryptedJson(new TextEncoder().encode(JSON.stringify(challenge)));327328  const proofBytes = await receiveEncryptedJson();329  const proofFrame = JSON.parse(new TextDecoder().decode(proofBytes)) as AuthProofFrame;330  if (proofFrame.type !== "PROOF") {331    throw new Error("expected PROOF frame");332  }333334  const initiatorPublicKey = hexToBytes(proofFrame.initiator_public_key_hex);335  const claimedProof = hexToBytes(proofFrame.proof_hex);336  if (initiatorPublicKey.length !== 32) {337    throw new Error("initiator public key must be 32 bytes");338  }339  if (claimedProof.length !== 32) {340    throw new Error("proof must be 32 bytes");341  }342343  // mac_for(our_priv, initiator_pub_for_dh, initiator_pub, our_pub, nonce)344  const dh = sharedKey(ourPrivateKey, initiatorPublicKey);345  const mac = new HMAC(SHA256, dh);346  mac.update(AUTH_DOMAIN);347  mac.update(initiatorPublicKey);348  mac.update(ourPublicKey);349  mac.update(nonce);350  const expected = mac.digest();351352  if (!constantTimeEq(expected, claimedProof)) {353    throw new Error("auth proof did not verify");354  }355  return { initiatorPublicKey };356}357358export async function performInitiatorAuth(359  session: NoiseNKSession,360  ourPrivateKey: Uint8Array,361  ourPublicKey: Uint8Array,362  responderPublicKey: Uint8Array,363  sendEncryptedJson: (data: Uint8Array) => Promise<void>,364  receiveEncryptedJson: () => Promise<Uint8Array>,365): Promise<void> {366  void session; // hash bound into MAC via the DH key only — kept for future fields367368  const challengeBytes = await receiveEncryptedJson();369  const challenge = JSON.parse(new TextDecoder().decode(challengeBytes)) as AuthChallengeFrame;370  if (challenge.type !== "CHALLENGE") {371    throw new Error("expected CHALLENGE frame");372  }373  const nonce = hexToBytes(challenge.nonce_hex);374  const responderKeyFromChallenge = hexToBytes(challenge.responder_public_key_hex);375  // Defence against an off-key challenge: the responder's claimed key MUST be376  // the one we Noise-NK-handshook against, otherwise an active MITM that377  // managed to substitute a different key is rerouting the auth round.378  if (379    responderKeyFromChallenge.length !== responderPublicKey.length ||380    !responderKeyFromChallenge.every((b, i) => b === responderPublicKey[i])381  ) {382    throw new Error("responder key in challenge does not match Noise handshake");383  }384385  const proof = computeAuthProof(ourPrivateKey, ourPublicKey, responderPublicKey, nonce);386  const proofFrame: AuthProofFrame = {387    type: "PROOF",388    initiator_public_key_hex: bytesToHex(ourPublicKey),389    proof_hex: bytesToHex(proof),390  };391  await sendEncryptedJson(new TextEncoder().encode(JSON.stringify(proofFrame)));392}393394export { bytesToHex, hexToBytes };