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 { HKDF } from "@stablelib/hkdf";23import { SHA256 } from "@stablelib/sha256";2425const PROTOCOL_NAME = "Noise_XX_25519_ChaChaPoly_BLAKE2s";2627function initHash(): Uint8Array {28  const nameBytes = new TextEncoder().encode(PROTOCOL_NAME);29  if (nameBytes.length <= 32) {30    const h = new Uint8Array(32);31    h.set(nameBytes);32    return h;33  }34  const sha = new SHA256();35  sha.update(nameBytes);36  return sha.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}4546function hkdf2(ck: Uint8Array, ikm: Uint8Array): [Uint8Array, Uint8Array] {47  const out = new HKDF(SHA256, ikm, ck).expand(64);48  return [out.slice(0, 32), out.slice(32, 64)];49}5051function nonceBytes(n: bigint): Uint8Array {52  const buf = new Uint8Array(12);53  new DataView(buf.buffer).setBigUint64(4, n, true);54  return buf;55}5657export interface NoiseXXSession {58  encrypt(plaintext: Uint8Array): Uint8Array;59  decrypt(ciphertext: Uint8Array): Uint8Array;60  remoteStaticPublicKey: Uint8Array;61  handshakeHash: Uint8Array;62}6364/**65 * Drive the XX initiator. The responder's static key is learned in66 * message 2; we hand it back so the caller can verify it against the67 * paired-device registry.68 */69export async function noiseXXInitiator(70  ourStaticPrivateKey: Uint8Array,71  ourStaticPublicKey: Uint8Array,72  send: (msg: Uint8Array) => Promise<void>,73  receive: () => Promise<Uint8Array>,74): Promise<NoiseXXSession> {75  let h: Uint8Array = initHash();76  let ck: Uint8Array = h.slice();7778  // --- Message 1: -> e ---79  const e = generateKeyPair();80  h = mixHash(h, e.publicKey);81  await send(e.publicKey);8283  // --- Message 2: <- e, ee, s, es ---84  const msg2 = await receive();85  if (msg2.length < 32 + 32 + 16 + 16) {86    throw new Error("Noise XX: msg2 too short");87  }88  const remoteEphemeral = msg2.slice(0, 32);89  const encryptedStatic = msg2.slice(32, 32 + 32 + 16);90  const encryptedPayload = msg2.slice(32 + 32 + 16);9192  h = mixHash(h, remoteEphemeral);93  const ee = sharedKey(e.secretKey, remoteEphemeral);94  const [ck1, k1] = hkdf2(ck, ee);95  ck = ck1;9697  const cipherStatic = new ChaCha20Poly1305(k1);98  const remoteStaticPlain = cipherStatic.open(nonceBytes(0n), encryptedStatic, h);99  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {100    throw new Error("Noise XX: msg2 static auth failed");101  }102  h = mixHash(h, encryptedStatic);103104  const es = sharedKey(e.secretKey, remoteStaticPlain);105  const [ck2, k2] = hkdf2(ck, es);106  ck = ck2;107108  const cipherPayload = new ChaCha20Poly1305(k2);109  const payloadPlain = cipherPayload.open(nonceBytes(0n), encryptedPayload, h);110  if (!payloadPlain) {111    throw new Error("Noise XX: msg2 payload auth failed");112  }113  h = mixHash(h, encryptedPayload);114115  // --- Message 3: -> s, se ---116  const cipherOurStatic = new ChaCha20Poly1305(k2);117  const encryptedOurStatic = cipherOurStatic.seal(nonceBytes(1n), ourStaticPublicKey, h);118  h = mixHash(h, encryptedOurStatic);119120  const se = sharedKey(ourStaticPrivateKey, remoteEphemeral);121  const [ck3, k3] = hkdf2(ck, se);122  ck = ck3;123124  const cipherFinal = new ChaCha20Poly1305(k3);125  const encryptedFinalPayload = cipherFinal.seal(nonceBytes(0n), new Uint8Array(0), h);126  h = mixHash(h, encryptedFinalPayload);127128  const msg3 = new Uint8Array(encryptedOurStatic.length + encryptedFinalPayload.length);129  msg3.set(encryptedOurStatic, 0);130  msg3.set(encryptedFinalPayload, encryptedOurStatic.length);131  await send(msg3);132133  // --- Transport keys: split (k_init_send, k_resp_send) ---134  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));135  const sendCipher = new ChaCha20Poly1305(initSend);136  const recvCipher = new ChaCha20Poly1305(respSend);137  let sendNonce = 0n;138  let recvNonce = 0n;139140  return {141    encrypt(plaintext) {142      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));143    },144    decrypt(ciphertext) {145      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));146      if (!result) throw new Error("Noise XX: decryption failed");147      return result;148    },149    remoteStaticPublicKey: remoteStaticPlain,150    handshakeHash: h.slice(),151  };152}153154/**155 * Drive the XX responder. The initiator's static key is learned in156 * message 3; we hand it back on success.157 */158export async function noiseXXResponder(159  ourStaticPrivateKey: Uint8Array,160  ourStaticPublicKey: Uint8Array,161  send: (msg: Uint8Array) => Promise<void>,162  receive: () => Promise<Uint8Array>,163): Promise<NoiseXXSession> {164  let h: Uint8Array = initHash();165  let ck: Uint8Array = h.slice();166167  // --- Message 1: <- e ---168  const msg1 = await receive();169  if (msg1.length < 32) throw new Error("Noise XX: msg1 too short");170  const remoteEphemeral = msg1.slice(0, 32);171  h = mixHash(h, remoteEphemeral);172173  // --- Message 2: -> e, ee, s, es ---174  const e = generateKeyPair();175  h = mixHash(h, e.publicKey);176  const ee = sharedKey(e.secretKey, remoteEphemeral);177  const [ck1, k1] = hkdf2(ck, ee);178  ck = ck1;179180  const cipherStatic = new ChaCha20Poly1305(k1);181  const encryptedOurStatic = cipherStatic.seal(nonceBytes(0n), ourStaticPublicKey, h);182  h = mixHash(h, encryptedOurStatic);183184  const es = sharedKey(ourStaticPrivateKey, remoteEphemeral);185  const [ck2, k2] = hkdf2(ck, es);186  ck = ck2;187188  const cipherPayload = new ChaCha20Poly1305(k2);189  const encryptedPayload = cipherPayload.seal(nonceBytes(0n), new Uint8Array(0), h);190  h = mixHash(h, encryptedPayload);191192  const msg2 = new Uint8Array(e.publicKey.length + encryptedOurStatic.length + encryptedPayload.length);193  msg2.set(e.publicKey, 0);194  msg2.set(encryptedOurStatic, e.publicKey.length);195  msg2.set(encryptedPayload, e.publicKey.length + encryptedOurStatic.length);196  await send(msg2);197198  // --- Message 3: <- s, se ---199  const msg3 = await receive();200  if (msg3.length < 32 + 16 + 16) throw new Error("Noise XX: msg3 too short");201  const encryptedRemoteStatic = msg3.slice(0, 32 + 16);202  const encryptedFinalPayload = msg3.slice(32 + 16);203204  const cipherTheirStatic = new ChaCha20Poly1305(k2);205  const remoteStaticPlain = cipherTheirStatic.open(nonceBytes(1n), encryptedRemoteStatic, h);206  if (!remoteStaticPlain || remoteStaticPlain.length !== 32) {207    throw new Error("Noise XX: msg3 static auth failed");208  }209  h = mixHash(h, encryptedRemoteStatic);210211  const se = sharedKey(e.secretKey, remoteStaticPlain);212  const [ck3, k3] = hkdf2(ck, se);213  ck = ck3;214215  const cipherFinal = new ChaCha20Poly1305(k3);216  const finalPayloadPlain = cipherFinal.open(nonceBytes(0n), encryptedFinalPayload, h);217  if (!finalPayloadPlain) {218    throw new Error("Noise XX: msg3 final payload auth failed");219  }220  h = mixHash(h, encryptedFinalPayload);221222  const [initSend, respSend] = hkdf2(ck, new Uint8Array(0));223  const sendCipher = new ChaCha20Poly1305(respSend);224  const recvCipher = new ChaCha20Poly1305(initSend);225  let sendNonce = 0n;226  let recvNonce = 0n;227228  return {229    encrypt(plaintext) {230      return sendCipher.seal(nonceBytes(sendNonce++), plaintext, new Uint8Array(0));231    },232    decrypt(ciphertext) {233      const result = recvCipher.open(nonceBytes(recvNonce++), ciphertext, new Uint8Array(0));234      if (!result) throw new Error("Noise XX: decryption failed");235      return result;236    },237    remoteStaticPublicKey: remoteStaticPlain,238    handshakeHash: h.slice(),239  };240}