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  // PCH-02-009: reject all-zero DH outputs from low-order peer points before109  // they enter the key schedule. Honest peers are unaffected.110  const ee = sharedKey(e.secretKey, remoteEphemeral, true);111  const [ck1, k1] = hkdf2(ck, ee);112  ck = ck1;113114  const cipherStatic = new ChaCha20Poly1305(k1);115  const remoteStaticPlain = cipherStatic.open(nonceBytes(0n), encryptedStatic, h);116  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {117    throw new Error("Noise XX: msg2 static auth failed");118  }119  h = mixHash(h, encryptedStatic);120121  const es = sharedKey(e.secretKey, remoteStaticPlain, true);122  const [ck2, k2] = hkdf2(ck, es);123  ck = ck2;124125  const cipherPayload = new ChaCha20Poly1305(k2);126  const payloadPlain = cipherPayload.open(nonceBytes(0n), encryptedPayload, h);127  if (!payloadPlain) {128    throw new Error("Noise XX: msg2 payload auth failed");129  }130  h = mixHash(h, encryptedPayload);131132  // PCH-01-003: pin the responder static BEFORE we transmit our own static in133  // msg3. `remoteStaticPlain` was authenticated above (msg2). If the caller's134  // check throws, we return without sending msg3 — our identity stays private.135  if (verifyRemoteStatic) verifyRemoteStatic(remoteStaticPlain);136137  // --- Message 3: -> s, se ---138  const cipherOurStatic = new ChaCha20Poly1305(k2);139  const encryptedOurStatic = cipherOurStatic.seal(nonceBytes(1n), ourStaticPublicKey, h);140  h = mixHash(h, encryptedOurStatic);141142  const se = sharedKey(ourStaticPrivateKey, remoteEphemeral, true);143  const [ck3, k3] = hkdf2(ck, se);144  ck = ck3;145146  const cipherFinal = new ChaCha20Poly1305(k3);147  const encryptedFinalPayload = cipherFinal.seal(nonceBytes(0n), new Uint8Array(0), h);148  h = mixHash(h, encryptedFinalPayload);149150  const msg3 = new Uint8Array(encryptedOurStatic.length + encryptedFinalPayload.length);151  msg3.set(encryptedOurStatic, 0);152  msg3.set(encryptedFinalPayload, encryptedOurStatic.length);153  await send(msg3);154155  // --- Transport keys: split (k_init_send, k_resp_send) ---156  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));157  const sendCipher = new ChaCha20Poly1305(initSend);158  const recvCipher = new ChaCha20Poly1305(respSend);159  let sendNonce = 0n;160  let recvNonce = 0n;161162  return {163    encrypt(plaintext) {164      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));165    },166    decrypt(ciphertext) {167      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));168      if (!result) throw new Error("Noise XX: decryption failed");169      return result;170    },171    remoteStaticPublicKey: remoteStaticPlain,172    handshakeHash: h.slice(),173  };174}175176/**177 * Drive the XX responder. The initiator's static key is learned in178 * message 3; we hand it back on success.179 */180export async function noiseXXResponder(181  ourStaticPrivateKey: Uint8Array,182  ourStaticPublicKey: Uint8Array,183  send: (msg: Uint8Array) => Promise<void>,184  receive: () => Promise<Uint8Array>,185): Promise<NoiseXXSession> {186  let h: Uint8Array = initHash();187  let ck: Uint8Array = h.slice();188189  // --- Message 1: <- e ---190  const msg1 = await receive();191  if (msg1.length < 32) throw new Error("Noise XX: msg1 too short");192  const remoteEphemeral = msg1.slice(0, 32);193  h = mixHash(h, remoteEphemeral);194195  // --- Message 2: -> e, ee, s, es ---196  const e = generateKeyPair();197  h = mixHash(h, e.publicKey);198  const ee = sharedKey(e.secretKey, remoteEphemeral, true);199  const [ck1, k1] = hkdf2(ck, ee);200  ck = ck1;201202  const cipherStatic = new ChaCha20Poly1305(k1);203  const encryptedOurStatic = cipherStatic.seal(nonceBytes(0n), ourStaticPublicKey, h);204  h = mixHash(h, encryptedOurStatic);205206  const es = sharedKey(ourStaticPrivateKey, remoteEphemeral, true);207  const [ck2, k2] = hkdf2(ck, es);208  ck = ck2;209210  const cipherPayload = new ChaCha20Poly1305(k2);211  const encryptedPayload = cipherPayload.seal(nonceBytes(0n), new Uint8Array(0), h);212  h = mixHash(h, encryptedPayload);213214  const msg2 = new Uint8Array(e.publicKey.length + encryptedOurStatic.length + encryptedPayload.length);215  msg2.set(e.publicKey, 0);216  msg2.set(encryptedOurStatic, e.publicKey.length);217  msg2.set(encryptedPayload, e.publicKey.length + encryptedOurStatic.length);218  await send(msg2);219220  // --- Message 3: <- s, se ---221  const msg3 = await receive();222  if (msg3.length < 32 + 16 + 16) throw new Error("Noise XX: msg3 too short");223  const encryptedRemoteStatic = msg3.slice(0, 32 + 16);224  const encryptedFinalPayload = msg3.slice(32 + 16);225226  const cipherTheirStatic = new ChaCha20Poly1305(k2);227  const remoteStaticPlain = cipherTheirStatic.open(nonceBytes(1n), encryptedRemoteStatic, h);228  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {229    throw new Error("Noise XX: msg3 static auth failed");230  }231  h = mixHash(h, encryptedRemoteStatic);232233  const se = sharedKey(e.secretKey, remoteStaticPlain, true);234  const [ck3, k3] = hkdf2(ck, se);235  ck = ck3;236237  const cipherFinal = new ChaCha20Poly1305(k3);238  const finalPayloadPlain = cipherFinal.open(nonceBytes(0n), encryptedFinalPayload, h);239  if (!finalPayloadPlain) {240    throw new Error("Noise XX: msg3 final payload auth failed");241  }242  h = mixHash(h, encryptedFinalPayload);243244  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));245  const sendCipher = new ChaCha20Poly1305(respSend);246  const recvCipher = new ChaCha20Poly1305(initSend);247  let sendNonce = 0n;248  let recvNonce = 0n;249250  return {251    encrypt(plaintext) {252      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));253    },254    decrypt(ciphertext) {255      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));256      if (!result) throw new Error("Noise XX: decryption failed");257      return result;258    },259    remoteStaticPublicKey: remoteStaticPlain,260    handshakeHash: h.slice(),261  };262}