noise-xx.ts

1// Noise XX (mutual auth) — used for every Phase-2 WebSocket connection2// after the audio chirp pairing has stamped each side into the other's3// paired-device registry. Both peers hold a long-term X25519 static key4// (the sync identity); XX is the canonical pattern when both parties want5// to authenticate each other.6//7// Pattern: Noise_XX_25519_ChaChaPoly_BLAKE2s — same primitives as the8// NK pattern in `noise-js.ts`, so the helpers are duplicated minimally9// (initHash / mixHash / hkdf2) to keep this file self-contained.10//11//   -> e12//   <- e, ee, s, es13//   -> s, se14//15// After msg 3, the symmetric `hkdf2(ck, "")` splits into two ChaCha20-16// Poly1305 transport keys, one per direction. Counter nonces start at 017// and increment per frame.1819import { generateKeyPair, sharedKey } from "@stablelib/x25519";20import { ChaCha20Poly1305 } from "@stablelib/chacha20poly1305";21import { BLAKE2s } from "@stablelib/blake2s";22import { HMAC } from "@stablelib/hmac";2324const PROTOCOL_NAME = "Noise_XX_25519_ChaChaPoly_BLAKE2s";2526export function initHash(): Uint8Array {27  const nameBytes = new TextEncoder().encode(PROTOCOL_NAME);28  if (nameBytes.length <= 32) {29    const h = new Uint8Array(32);30    h.set(nameBytes);31    return h;32  }33  // PCH-01-002: the named pattern hash is BLAKE2s; the protocol-name init hash34  // MUST use it too (Noise spec §5.2), not SHA-256. BLAKE2s digest is 32 bytes,35  // matching mixHash output width.36  return new BLAKE2s(32).update(nameBytes).digest();37}3839function mixHash(h: Uint8Array, data: Uint8Array): Uint8Array {40  const blake = new BLAKE2s(32);41  blake.update(h);42  blake.update(data);43  return blake.digest();44}4546export function hkdf2(ck: Uint8Array, ikm: Uint8Array): [Uint8Array, Uint8Array] {47  // PCH-01-002: HKDF must run over the named hash (BLAKE2s), not SHA-256.48  // @stablelib's HKDF reuses one HMAC across output blocks and BLAKE2s's49  // restoreState() never clears its `finished` flag, so `new HKDF(BLAKE2s, …)`50  // throws "can't update because hash was finished". Run standard HKDF-Expand51  // (RFC 5869, empty info) with a FRESH HMAC-BLAKE2s per block instead — this is52  // byte-identical to BouncyCastle `HKDFBytesGenerator(Blake2sDigest(256))` on53  // the peach-android side, so the two stay in wire lockstep.54  const prk = new HMAC(BLAKE2s, ck).update(ikm).digest(); // Extract (salt=ck)55  const k1 = new HMAC(BLAKE2s, prk).update(Uint8Array.of(1)).digest();56  const k2 = new HMAC(BLAKE2s, prk).update(k1).update(Uint8Array.of(2)).digest();57  return [k1, k2];58}5960function nonceBytes(n: bigint): Uint8Array {61  const buf = new Uint8Array(12);62  new DataView(buf.buffer).setBigUint64(4, n, true);63  return buf;64}6566export interface NoiseXXSession {67  encrypt(plaintext: Uint8Array): Uint8Array;68  decrypt(ciphertext: Uint8Array): Uint8Array;69  remoteStaticPublicKey: Uint8Array;70  handshakeHash: Uint8Array;71}7273/**74 * Drive the XX initiator. The responder's static key is learned in75 * message 2; we hand it back so the caller can verify it against the76 * paired-device registry.77 */78export async function noiseXXInitiator(79  ourStaticPrivateKey: Uint8Array,80  ourStaticPublicKey: Uint8Array,81  send: (msg: Uint8Array) => Promise<void>,82  receive: () => Promise<Uint8Array>,83  // PCH-01-003: called once the responder's static is authenticated (end of84  // msg2) and BEFORE msg3 — which carries OUR static — is sent. Throwing here85  // aborts the handshake without disclosing our long-term identity to an86  // unexpected peer. Honest callers pass a pin check; omitting it preserves the87  // old behaviour.88  verifyRemoteStatic?: (remoteStaticPublicKey: Uint8Array) => void,89): Promise<NoiseXXSession> {90  let h: Uint8Array = initHash();91  let ck: Uint8Array = h.slice();9293  // --- Message 1: -> e ---94  const e = generateKeyPair();95  h = mixHash(h, e.publicKey);96  await send(e.publicKey);9798  // --- Message 2: <- e, ee, s, es ---99  const msg2 = await receive();100  if (msg2.length < 32 + 32 + 16 + 16) {101    throw new Error("Noise XX: msg2 too short");102  }103  const remoteEphemeral = msg2.slice(0, 32);104  const encryptedStatic = msg2.slice(32, 32 + 32 + 16);105  const encryptedPayload = msg2.slice(32 + 32 + 16);106107  h = mixHash(h, remoteEphemeral);108  const ee = sharedKey(e.secretKey, remoteEphemeral);109  const [ck1, k1] = hkdf2(ck, ee);110  ck = ck1;111112  const cipherStatic = new ChaCha20Poly1305(k1);113  const remoteStaticPlain = cipherStatic.open(nonceBytes(0n), encryptedStatic, h);114  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {115    throw new Error("Noise XX: msg2 static auth failed");116  }117  h = mixHash(h, encryptedStatic);118119  const es = sharedKey(e.secretKey, remoteStaticPlain);120  const [ck2, k2] = hkdf2(ck, es);121  ck = ck2;122123  const cipherPayload = new ChaCha20Poly1305(k2);124  const payloadPlain = cipherPayload.open(nonceBytes(0n), encryptedPayload, h);125  if (!payloadPlain) {126    throw new Error("Noise XX: msg2 payload auth failed");127  }128  h = mixHash(h, encryptedPayload);129130  // PCH-01-003: pin the responder static BEFORE we transmit our own static in131  // msg3. `remoteStaticPlain` was authenticated above (msg2). If the caller's132  // check throws, we return without sending msg3 — our identity stays private.133  if (verifyRemoteStatic) verifyRemoteStatic(remoteStaticPlain);134135  // --- Message 3: -> s, se ---136  const cipherOurStatic = new ChaCha20Poly1305(k2);137  const encryptedOurStatic = cipherOurStatic.seal(nonceBytes(1n), ourStaticPublicKey, h);138  h = mixHash(h, encryptedOurStatic);139140  const se = sharedKey(ourStaticPrivateKey, remoteEphemeral);141  const [ck3, k3] = hkdf2(ck, se);142  ck = ck3;143144  const cipherFinal = new ChaCha20Poly1305(k3);145  const encryptedFinalPayload = cipherFinal.seal(nonceBytes(0n), new Uint8Array(0), h);146  h = mixHash(h, encryptedFinalPayload);147148  const msg3 = new Uint8Array(encryptedOurStatic.length + encryptedFinalPayload.length);149  msg3.set(encryptedOurStatic, 0);150  msg3.set(encryptedFinalPayload, encryptedOurStatic.length);151  await send(msg3);152153  // --- Transport keys: split (k_init_send, k_resp_send) ---154  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));155  const sendCipher = new ChaCha20Poly1305(initSend);156  const recvCipher = new ChaCha20Poly1305(respSend);157  let sendNonce = 0n;158  let recvNonce = 0n;159160  return {161    encrypt(plaintext) {162      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));163    },164    decrypt(ciphertext) {165      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));166      if (!result) throw new Error("Noise XX: decryption failed");167      return result;168    },169    remoteStaticPublicKey: remoteStaticPlain,170    handshakeHash: h.slice(),171  };172}173174/**175 * Drive the XX responder. The initiator's static key is learned in176 * message 3; we hand it back on success.177 */178export async function noiseXXResponder(179  ourStaticPrivateKey: Uint8Array,180  ourStaticPublicKey: Uint8Array,181  send: (msg: Uint8Array) => Promise<void>,182  receive: () => Promise<Uint8Array>,183): Promise<NoiseXXSession> {184  let h: Uint8Array = initHash();185  let ck: Uint8Array = h.slice();186187  // --- Message 1: <- e ---188  const msg1 = await receive();189  if (msg1.length < 32) throw new Error("Noise XX: msg1 too short");190  const remoteEphemeral = msg1.slice(0, 32);191  h = mixHash(h, remoteEphemeral);192193  // --- Message 2: -> e, ee, s, es ---194  const e = generateKeyPair();195  h = mixHash(h, e.publicKey);196  const ee = sharedKey(e.secretKey, remoteEphemeral);197  const [ck1, k1] = hkdf2(ck, ee);198  ck = ck1;199200  const cipherStatic = new ChaCha20Poly1305(k1);201  const encryptedOurStatic = cipherStatic.seal(nonceBytes(0n), ourStaticPublicKey, h);202  h = mixHash(h, encryptedOurStatic);203204  const es = sharedKey(ourStaticPrivateKey, remoteEphemeral);205  const [ck2, k2] = hkdf2(ck, es);206  ck = ck2;207208  const cipherPayload = new ChaCha20Poly1305(k2);209  const encryptedPayload = cipherPayload.seal(nonceBytes(0n), new Uint8Array(0), h);210  h = mixHash(h, encryptedPayload);211212  const msg2 = new Uint8Array(e.publicKey.length + encryptedOurStatic.length + encryptedPayload.length);213  msg2.set(e.publicKey, 0);214  msg2.set(encryptedOurStatic, e.publicKey.length);215  msg2.set(encryptedPayload, e.publicKey.length + encryptedOurStatic.length);216  await send(msg2);217218  // --- Message 3: <- s, se ---219  const msg3 = await receive();220  if (msg3.length < 32 + 16 + 16) throw new Error("Noise XX: msg3 too short");221  const encryptedRemoteStatic = msg3.slice(0, 32 + 16);222  const encryptedFinalPayload = msg3.slice(32 + 16);223224  const cipherTheirStatic = new ChaCha20Poly1305(k2);225  const remoteStaticPlain = cipherTheirStatic.open(nonceBytes(1n), encryptedRemoteStatic, h);226  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {227    throw new Error("Noise XX: msg3 static auth failed");228  }229  h = mixHash(h, encryptedRemoteStatic);230231  const se = sharedKey(e.secretKey, remoteStaticPlain);232  const [ck3, k3] = hkdf2(ck, se);233  ck = ck3;234235  const cipherFinal = new ChaCha20Poly1305(k3);236  const finalPayloadPlain = cipherFinal.open(nonceBytes(0n), encryptedFinalPayload, h);237  if (!finalPayloadPlain) {238    throw new Error("Noise XX: msg3 final payload auth failed");239  }240  h = mixHash(h, encryptedFinalPayload);241242  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));243  const sendCipher = new ChaCha20Poly1305(respSend);244  const recvCipher = new ChaCha20Poly1305(initSend);245  let sendNonce = 0n;246  let recvNonce = 0n;247248  return {249    encrypt(plaintext) {250      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));251    },252    decrypt(ciphertext) {253      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));254      if (!result) throw new Error("Noise XX: decryption failed");255      return result;256    },257    remoteStaticPublicKey: remoteStaticPlain,258    handshakeHash: h.slice(),259  };260}