Merge branch 'master' into boltz-swaps

# Conflicts:
#	src/api.js
#	src/app.js

1 files changed, 242 insertions, 12 deletions

diff --git a/src/silentpay.js b/src/silentpay.js
index 0700999..eeabc1a 100644
--- a/src/silentpay.js
+++ b/src/silentpay.js
@@ -1,4 +1,4 @@
-// Silent Payments (BIP-352) — sending side only.
+// Silent Payments (BIP-352) — sending and receiving.
 //
 // A silent payment address (sp1…) is a static, reusable address the receiver
 // publishes once. The sender derives a unique one-time taproot output for each
@@ -6,20 +6,21 @@
 // so there's no on-chain link between payments and no address reuse — without
 // any interaction with the receiver.
 //
-// This module only does the SENDER half (deriving the output). Receiving needs
-// chain scanning (a per-tx ECDH tweak), which a light client can't do without a
-// dedicated index server — out of scope here.
+// Sending (silentPaymentScripts) derives the output; we only spend compressed
+// P2WPKH inputs, so each input contributes its private key as-is. Receiving (see
+// the second half) can't scan the chain in a browser, so an indexing server
+// supplies per-tx tweaks + taproot UTXOs and we match them on-device.
 //
-// Validated against the official BIP-352 send test vectors. We only spend
-// compressed P2WPKH inputs, which keeps the eligible-input rules trivial: each
-// input contributes its private key as-is (no taproot even-Y negation, no
-// uncompressed-key or P2SH edge cases).
+// Validated against the official BIP-352 send + receive test vectors.
 
 import { secp256k1 } from '@noble/curves/secp256k1';
 import { sha256 } from '@noble/hashes/sha256';
+import { ripemd160 } from '@noble/hashes/ripemd160';
 import { hexToBytes, bytesToHex, concatBytes } from '@noble/hashes/utils';
 import { bech32m } from '@scure/base';
 
+const hash160 = (b) => ripemd160(sha256(b));
+
 const Point = secp256k1.ProjectivePoint;
 const G = Point.BASE;
 const N = secp256k1.CURVE.n;
@@ -68,17 +69,24 @@ export function decodeSilentPaymentAddress(addr) {
 
 // Derive the one-time taproot output scripts for a set of silent-payment outputs
 // that this transaction's inputs are funding.
-//   inputs:  [{ txid (display hex), vout, priv (Uint8Array 32) }] — ALL eligible
-//            (P2WPKH) inputs of the tx; the derivation commits to every one.
+//   inputs:  [{ txid (display hex), vout, priv (Uint8Array 32), taproot? }] — ALL
+//            eligible inputs of the tx; the derivation commits to every one. Set
+//            taproot:true for P2TR inputs (e.g. our own silent-payment coins) so
+//            their key is taken with even Y, per BIP-352.
 //   outputs: [{ scan, spend }] — one entry per desired output (repeat the same
 //            recipient to pay it multiple times; the k counter is handled here).
 // Returns a taproot scriptPubKey (Uint8Array) for each entry, in order.
 export function silentPaymentScripts(inputs, outputs) {
   if (!inputs.length) throw new Error('Silent payment needs at least one input.');
 
-  // a = Σ input private keys (mod n); A = a·G
+  // a = Σ input private keys (mod n); A = a·G. A taproot input contributes the
+  // key for its even-Y x-only pubkey, so negate when the key gives odd Y.
   let a = 0n;
-  for (const i of inputs) a = modN(a + toInt(i.priv));
+  for (const i of inputs) {
+    let d = toInt(i.priv);
+    if (i.taproot && Number(G.multiply(d).toRawBytes(true)[0]) === 0x03) d = modN(-d);
+    a = modN(a + d);
+  }
   if (a === 0n) throw new Error('Silent payment input key sum is zero.');
   const A = G.multiply(a);
 
@@ -109,3 +117,225 @@ export function silentPaymentScripts(inputs, outputs) {
 export function silentPaymentPlaceholder(index) {
   return taprootScript(sha256(concatBytes(new TextEncoder().encode('halsp-placeholder'), be32(index))));
 }
+
+// ===========================================================================
+// Receiving (BIP-352).
+//
+// A browser light client can't scan the chain itself, so an indexing server (an
+// SP "oracle") provides, per block, the tweaks — one 33-byte point (input_hash·A,
+// the sum of a tx's eligible input pubkeys folded with its input hash) per
+// eligible transaction — plus the taproot UTXOs created in that block. The
+// receiver then does the private part on-device: ecdh = b_scan · tweak, then for
+// k = 0,1,… derives P_k = B_spend + t_k·G and matches it against the block's
+// outputs. The scan key never leaves the device.
+//
+// The first half here (input pubkey extraction + tweak) is what the indexer
+// computes from raw blocks; the second half (scan, output key, key derivation,
+// address) is what the wallet uses. They share one implementation so the math
+// is validated once, against the official BIP-352 vectors.
+// ===========================================================================
+
+const numTo32 = (x) => hexToBytes(x.toString(16).padStart(64, '0'));
+
+// secp256k1 NUMS point H (BIP-341): a taproot input whose script-path reveals
+// this as the internal key is provably unspendable and NOT an eligible input.
+const NUMS_H = '50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0';
+
+// Parse a serialized witness (hex): compact-size item count, then each item as
+// compact-size length + bytes.
+function parseWitness(hex) {
+  if (!hex) return [];
+  const b = hexToBytes(hex);
+  let o = 0;
+  const rd = () => {
+    let n = b[o++];
+    if (n === 0xfd) { n = b[o] | (b[o + 1] << 8); o += 2; }
+    else if (n === 0xfe) { n = b[o] | (b[o + 1] << 8) | (b[o + 2] << 16) | (b[o + 3] * 0x1000000); o += 4; }
+    return n;
+  };
+  const count = rd();
+  const items = [];
+  for (let i = 0; i < count; i++) { const len = rd(); items.push(b.slice(o, o + len)); o += len; }
+  return items;
+}
+
+// Witness stack items as byte arrays. Accepts either a serialized witness (hex
+// string, as in the BIP-352 vectors) or an array of hex stack items (as Core's
+// getblock RPC returns in txinwitness).
+function witnessItems(witness) {
+  if (Array.isArray(witness)) return witness.map(hexToBytes);
+  return parseWitness(witness);
+}
+
+// Pull the data pushes out of a scriptSig (hex) — enough to recover the pubkey
+// from P2PKH or the redeemScript from P2SH (push opcodes only).
+function scriptPushes(hex) {
+  if (!hex) return [];
+  const b = hexToBytes(hex);
+  let o = 0;
+  const pushes = [];
+  while (o < b.length) {
+    const op = b[o++];
+    let len = -1;
+    if (op >= 0x01 && op <= 0x4b) len = op;
+    else if (op === 0x4c) len = b[o++];
+    else if (op === 0x4d) { len = b[o] | (b[o + 1] << 8); o += 2; }
+    else if (op === 0x4e) { len = b[o] | (b[o + 1] << 8) | (b[o + 2] << 16) | (b[o + 3] * 0x1000000); o += 4; }
+    else continue; // non-push opcode
+    if (len < 0 || o + len > b.length) break;
+    pushes.push(b.slice(o, o + len)); o += len;
+  }
+  return pushes;
+}
+
+// Only compressed pubkeys are eligible — uncompressed-key inputs are skipped.
+const looksLikePubKey = (b) => !!b && b.length === 33 && (b[0] === 0x02 || b[0] === 0x03);
+
+// Recover the BIP-352-eligible input public key (33-byte compressed) from a tx
+// input, or null if the input type isn't eligible. Handles P2PKH, P2WPKH,
+// P2SH-P2WPKH and P2TR (key-path) inputs.
+export function inputPubKey({ scriptSig = '', witness = '', scriptPubKey = '' }) {
+  try {
+    const spk = hexToBytes(scriptPubKey);
+    // P2TR: OP_1 PUSH32 <x-only>
+    if (spk.length === 34 && spk[0] === 0x51 && spk[1] === 0x20) {
+      let w = witnessItems(witness);
+      if (w.length > 1 && w[w.length - 1][0] === 0x50) w = w.slice(0, -1); // strip annex
+      if (w.length > 1 && bytesToHex(w[w.length - 1].slice(1, 33)) === NUMS_H) return null; // NUMS script-path
+      return Point.fromHex(concatBytes(Uint8Array.of(0x02), spk.slice(2, 34))).toRawBytes(true); // even-Y lift
+    }
+    // P2WPKH: OP_0 PUSH20
+    if (spk.length === 22 && spk[0] === 0x00 && spk[1] === 0x14) {
+      const w = witnessItems(witness);
+      const pk = w[w.length - 1];
+      return looksLikePubKey(pk) ? Point.fromHex(pk).toRawBytes(true) : null;
+    }
+    // P2SH-P2WPKH: scriptSig pushes redeemScript 0014<20>; witness = [sig, pubkey]
+    if (spk.length === 23 && spk[0] === 0xa9 && spk[1] === 0x14 && spk[22] === 0x87) {
+      const rs = scriptPushes(scriptSig)[0];
+      if (!rs || rs.length !== 22 || rs[0] !== 0x00 || rs[1] !== 0x14) return null;
+      const w = witnessItems(witness);
+      const pk = w[w.length - 1];
+      return looksLikePubKey(pk) ? Point.fromHex(pk).toRawBytes(true) : null;
+    }
+    // P2PKH: OP_DUP OP_HASH160 PUSH20 <hash> ... — the eligible pubkey is the
+    // scriptSig push whose hash160 matches <hash> (handles malleated scriptSigs).
+    if (spk.length === 25 && spk[0] === 0x76 && spk[1] === 0xa9 && spk[2] === 0x14) {
+      const target = bytesToHex(spk.slice(3, 23));
+      const pushes = scriptPushes(scriptSig);
+      for (let i = pushes.length - 1; i >= 0; i--) {
+        const pk = pushes[i];
+        if (looksLikePubKey(pk) && bytesToHex(hash160(pk)) === target) return Point.fromHex(pk).toRawBytes(true);
+      }
+      return null;
+    }
+  } catch {}
+  return null;
+}
+
+// The oracle tweak for a transaction: 33-byte point input_hash·A, where A is the
+// sum of the eligible input pubkeys and input_hash = H_BIP0352/Inputs(outpoint_L
+// || A) with outpoint_L the smallest outpoint among ALL the tx's inputs.
+//   inputs: [{ txid (display hex), vout, pubkey? (Uint8Array 33) }] — every input
+//           of the tx; `pubkey` present only for BIP-352-eligible inputs.
+// Returns null if the tx has no eligible inputs (so it can't be a silent payment).
+export function silentPaymentTweak(inputs) {
+  let A = null;
+  for (const i of inputs) if (i.pubkey) A = A ? A.add(Point.fromHex(i.pubkey)) : Point.fromHex(i.pubkey);
+  if (!A) return null;
+  let Abytes;
+  try { Abytes = A.toRawBytes(true); } catch { return null; } // A is the point at infinity → not a silent payment
+  let smallest = null;
+  for (const i of inputs) {
+    const op = concatBytes(hexToBytes(i.txid).reverse(), le32(i.vout));
+    if (!smallest || bytesToHex(op) < bytesToHex(smallest)) smallest = op;
+  }
+  const inputHash = modN(toInt(tagged('BIP0352/Inputs', concatBytes(smallest, Abytes))));
+  return A.multiply(inputHash).toRawBytes(true);
+}
+
+// Scan a transaction's taproot outputs for payments to us.
+//   scanPriv: Uint8Array(32)  our scan private key (b_scan)
+//   spendPub: Uint8Array(33)  our spend public key (B_spend)
+//   tweak:    Uint8Array(33)  the oracle tweak for this tx (input_hash·A)
+//   outputs:  array of 32-byte x-only output pubkeys (hex) in the tx
+// Returns the matched outputs: [{ output (x-only hex), k, tweak (t_k hex 32) }];
+// `tweak` (t_k) is added to the spend private key to spend the coin.
+export function silentPaymentScan({ scanPriv, spendPub, tweak, outputs, maxK = 30 }) {
+  const ecdh = Point.fromHex(tweak).multiply(modN(toInt(scanPriv))).toRawBytes(true);
+  const B = Point.fromHex(spendPub);
+  const remaining = new Set(outputs.map((o) => o.toLowerCase()));
+  const found = [];
+  for (let k = 0; k < maxK && remaining.size; k++) {
+    const tk = modN(toInt(tagged('BIP0352/SharedSecret', concatBytes(ecdh, be32(k)))));
+    const xonly = bytesToHex(B.add(G.multiply(tk)).toRawBytes(true).slice(1));
+    if (!remaining.has(xonly)) break; // no output at this k → done with this tx
+    found.push({ output: xonly, k, tweak: bytesToHex(numTo32(tk)) });
+    remaining.delete(xonly);
+  }
+  return found;
+}
+
+// Spend private key for a found SP output: d = (spend_priv + t_k) mod n. Used as
+// the taproot key-path key (the signer negates for odd-Y per BIP-340).
+export function silentPaymentOutputPrivKey(spendPriv, tweakK) {
+  return numTo32(modN(toInt(spendPriv) + toInt(tweakK)));
+}
+
+// Derive the BIP-352 scan + spend keys from a BIP32 master node.
+//   spend: m/352'/coin'/account'/0'/0   scan: m/352'/coin'/account'/1'/0
+export function deriveSilentPaymentKeys(master, coin, account = 0) {
+  const spend = master.derive(`m/352'/${coin}'/${account}'/0'/0`);
+  const scan = master.derive(`m/352'/${coin}'/${account}'/1'/0`);
+  return {
+    scanPriv: scan.privateKey, scanPub: scan.publicKey,
+    spendPriv: spend.privateKey, spendPub: spend.publicKey,
+  };
+}
+
+// Encode an sp1…/tsp1… address from scan + spend public keys (33 bytes each).
+export function encodeSilentPaymentAddress(scanPub, spendPub, { testnet = false } = {}) {
+  const hrp = testnet ? 'tsp' : 'sp';
+  const words = [0, ...bech32m.toWords(concatBytes(scanPub, spendPub))];
+  return bech32m.encode(hrp, words, 1023);
+}
+
+// ---- catch-up scaling: candidate keys + per-block Bloom filters -----------
+// For a large historical scan, downloading every block's outputs is wasteful.
+// The indexer gives, per block, the tweaks + a Bloom filter over that block's
+// taproot output keys. The client derives its candidate key P_0 from each tweak
+// and tests the filter; only on a hit does it pull the block's outputs and run
+// the full scan. (P_0 always exists if we're paid, so testing it alone suffices.)
+
+// Our candidate output key (P_0 = B_spend + t_0·G, x-only hex) for one tweak.
+export function silentPaymentCandidate({ scanPriv, spendPub, tweak }) {
+  const ecdh = Point.fromHex(tweak).multiply(modN(toInt(scanPriv))).toRawBytes(true);
+  const t0 = modN(toInt(tagged('BIP0352/SharedSecret', concatBytes(ecdh, be32(0)))));
+  return bytesToHex(Point.fromHex(spendPub).add(G.multiply(t0)).toRawBytes(true).slice(1));
+}
+
+// k bit indices for a 32-byte x-only key (hex) in an m-bit filter, via
+// double-hashing one sha256(key): idx_i = (h1 + i·h2) mod m.
+function* bloomIndices(keyHex, m, k) {
+  const h = sha256(hexToBytes(keyHex));
+  const u32 = (o) => (h[o] | (h[o + 1] << 8) | (h[o + 2] << 16) | (h[o + 3] * 0x1000000)) >>> 0;
+  const h1 = u32(0);
+  const h2 = u32(4) | 1; // odd, so it's coprime-ish with m
+  for (let i = 0; i < k; i++) yield ((h1 + i * h2) >>> 0) % m;
+}
+
+// Build a Bloom filter over x-only keys (hex). { m (bits), k (hashes), bits (hex) }.
+export function buildBloom(keysHex, bitsPerKey = 10, k = 7) {
+  const m = Math.max(8, keysHex.length * bitsPerKey);
+  const bytes = new Uint8Array(Math.ceil(m / 8));
+  for (const key of keysHex) for (const idx of bloomIndices(key, m, k)) bytes[idx >> 3] |= 1 << (idx & 7);
+  return { m, k, bits: bytesToHex(bytes) };
+}
+
+// Is an x-only key (hex) possibly in the filter? (false = definitely not.)
+export function bloomHas(filter, keyHex) {
+  if (!filter || !filter.m) return true; // no filter ⇒ can't rule out → scan it
+  const bytes = hexToBytes(filter.bits);
+  for (const idx of bloomIndices(keyHex, filter.m, filter.k)) if (!(bytes[idx >> 3] & (1 << (idx & 7)))) return false;
+  return true;
+}