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feat: per-user tweaked deposit addresses (Phase 2 of #267) #269

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Merged
melvincarvalho merged 2 commits into from
Apr 3, 2026
Merged

feat: per-user tweaked deposit addresses (Phase 2 of #267) #269

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0e18c4f
feat: per-user tweaked deposit addresses (Phase 2 of #267)
melvincarvalho Apr 3, 2026
5cae0d0
fix: tweaked UTXO fallback selection, validate user DID on address en…
melvincarvalho Apr 3, 2026
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67 changes: 49 additions & 18 deletions src/handlers/pay.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ import crypto from 'crypto';
import { getNostrPubkey, pubkeyToDidNostr } from '../auth/nostr.js';
import { readLedger, writeLedger, getBalance, credit, debit } from '../webledger.js';
import { verifyMrc20Deposit, verifyMrc20Anchor, jcs, btAddress } from '../mrc20.js';
import { loadTrail, transferToken, buildTransaction, broadcastTx, p2trScript } from '../token.js';
import { loadTrail, transferToken, buildTransaction, broadcastTx, p2trScript, btDeriveChainedPrivkey } from '../token.js';
import { secp256k1 } from '@noble/curves/secp256k1';
import { bytesToHex, hexToBytes } from '@noble/hashes/utils';
import fs from 'fs-extra';
Expand Down Expand Up @@ -282,7 +282,7 @@ export function createPayHandler(options = {}) {
return reply.send(info);
}

// --- GET /pay/.address — public deposit address ---
// --- GET /pay/.address — deposit address (optional per-user tweak) ---
if (url === '/pay/.address' && request.method === 'GET') {
const chain = request.query?.chain || (payChains ? payChains[0] : 'tbtc4');
if (!CHAIN_REGISTRY[chain]) {
Expand All @@ -293,8 +293,15 @@ export function createPayHandler(options = {}) {
}
const kp = await loadOrCreateKeypair();
const network = chain === 'btc' ? 'mainnet' : (chain === 'tbtc3' ? 'testnet' : 'testnet4');
const address = btAddress(kp.pubkey, [], network);
return reply.send({ address, chain, pubkey: kp.pubkey });
const user = request.query?.user?.trim().toLowerCase() || null;
if (user && !/^did:nostr:[0-9a-f]{64}$/.test(user)) {
return reply.code(400).send({ error: 'Invalid user DID. Expected: did:nostr:<64-hex>' });
}
const states = user ? [user] : [];
const address = btAddress(kp.pubkey, states, network);
const response = { address, chain, pubkey: kp.pubkey };
if (user) response.user = user;
return reply.send(response);
}

// --- GET /pay/.balance ---
Expand Down Expand Up @@ -435,8 +442,10 @@ export function createPayHandler(options = {}) {
return reply.code(400).send({ error: `Unknown chain: ${chainId}` });
}

// Derive pod's address for this chain
// Derive address — try per-user tweaked address first, fall back to generic
const network = chainId === 'btc' ? 'mainnet' : (chainId === 'tbtc3' ? 'testnet' : 'testnet4');
const didUri = pubkeyToDidNostr(pubkey);
const userAddress = btAddress(kp.pubkey, [didUri], network);
const podAddress = btAddress(kp.pubkey, [], network);

// Fetch transaction from mempool
Expand All @@ -455,24 +464,24 @@ export function createPayHandler(options = {}) {
return reply.code(400).send({ error: `Output ${deposit.vout} not found` });
}

// Verify output pays our address
if (output.scriptpubkey_address !== podAddress) {
return reply.code(400).send({ error: 'Output does not pay this pod\'s address', expected: podAddress });
// Verify output pays our address (per-user tweaked or generic pod address)
const outputAddr = output.scriptpubkey_address;
const tweak = outputAddr === userAddress ? didUri : null;
if (outputAddr !== userAddress && outputAddr !== podAddress) {
return reply.code(400).send({ error: 'Output does not pay this pod\'s address', expected: { user: userAddress, pod: podAddress } });
Comment on lines +467 to +471

Copilot AI Apr 3, 2026

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The claim handler now accepts both userAddress and podAddress, but the success response doesn’t indicate which address was actually matched. For troubleshooting/client correctness (especially with per-user addresses), consider including the matched outputAddr (and/or the resolved tweak) in the response payload.

Copilot uses AI. Check for mistakes.
}
Comment on lines +467 to 472

Copilot AI Apr 3, 2026

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When a claim matches the per-user tweaked address (outputAddr === userAddress) you correctly record tweak, but the success response later still returns address: podAddress (not the actual outputAddr). This makes the API response inconsistent with what was validated/credited. Consider returning the credited address (or both addresses + a flag indicating whether a tweak was used).

Copilot uses AI. Check for mistakes.

const amount = output.value;
const currency = chain.unit;

// Replay protection + UTXO tracking
const utxos = await loadUtxos();
const utxoKey = `${deposit.txid}:${deposit.vout}`;
if (utxos.find(u => u.txid === deposit.txid && u.vout === deposit.vout)) {
return reply.code(400).send({ error: 'This output has already been claimed' });
}
utxos.push({ txid: deposit.txid, vout: deposit.vout, amount, scriptpubkey: output.scriptpubkey, chain: chainId, spent: false });
utxos.push({ txid: deposit.txid, vout: deposit.vout, amount, scriptpubkey: output.scriptpubkey, chain: chainId, tweak, spent: false });
await saveUtxos(utxos);

const didUri = pubkeyToDidNostr(pubkey);
const ledger = await readLedger();
const newBalance = credit(ledger, didUri, amount, currency);
await writeLedger(ledger);
Expand Down Expand Up @@ -752,23 +761,45 @@ export function createPayHandler(options = {}) {
return reply.code(400).send({ error: 'No UTXOs available for withdrawal' });
}

// Select UTXOs (simple: pick first one that's big enough, or accumulate)
let selected = [];
let total = 0;
// Load pod keypair
const kp = await loadOrCreateKeypair();

// Select UTXOs — group by tweak so we can sign with one key
// Prefer untweaked UTXOs first, then tweaked ones
const fee = 300;
const needed = withdrawAmount + fee;
for (const utxo of available) {
let selected = [];
let total = 0;
let selectedTweak = null;

// Try untweaked first
for (const utxo of available.filter(u => !u.tweak)) {
selected.push(utxo);
total += utxo.amount;
if (total >= needed) break;
}
// If not enough, try tweaked (same tweak group only)
if (total < needed) {
const tweaked = available.filter(u => u.tweak);
selected = [];
total = 0;
selectedTweak = null;
for (const utxo of tweaked) {
if (selectedTweak && utxo.tweak !== selectedTweak) continue;
selected.push(utxo);
selectedTweak = utxo.tweak;
total += utxo.amount;
if (total >= needed) break;
Comment on lines +783 to +792

Copilot AI Apr 3, 2026

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The tweaked-UTXO selection loop picks the first tweak group it encounters (based on available order) and fails if that group can’t cover needed, even if a later tweak group (or a combination of untweaked + a tweak group) has enough total value. This can incorrectly return “Not enough UTXO value…” despite sufficient funds being present. Consider grouping available by tweak and selecting a group with sufficient total (e.g., smallest group that meets needed), or extend the transaction builder to support spending inputs from multiple tweak groups with per-input signing keys.

Suggested change
const tweaked = available.filter(u => u.tweak);
selected = [];
total = 0;
selectedTweak = null;
for (const utxo of tweaked) {
if (selectedTweak && utxo.tweak !== selectedTweak) continue;
selected.push(utxo);
selectedTweak = utxo.tweak;
total += utxo.amount;
if (total >= needed) break;
const tweakedGroups = new Map();
for (const utxo of available.filter(u => u.tweak)) {
if (!tweakedGroups.has(utxo.tweak)) tweakedGroups.set(utxo.tweak, []);
tweakedGroups.get(utxo.tweak).push(utxo);
}
const candidateGroups = Array.from(tweakedGroups.entries())
.map(([tweak, utxos]) => ({
tweak,
utxos,
total: utxos.reduce((sum, u) => sum + u.amount, 0),
}))
.filter(group => group.total >= needed)
.sort((a, b) => a.total - b.total);
selected = [];
total = 0;
selectedTweak = null;
if (candidateGroups.length > 0) {
const bestGroup = candidateGroups[0];
selectedTweak = bestGroup.tweak;
for (const utxo of bestGroup.utxos) {
selected.push(utxo);
total += utxo.amount;
if (total >= needed) break;
}

Copilot uses AI. Check for mistakes.
}
}
if (total < needed) {
return reply.code(400).send({ error: 'Not enough UTXO value for withdrawal + fee', available: total, needed });
}

// Load pod keypair
const kp = await loadOrCreateKeypair();
const privkeyBytes = hexToBytes(kp.privkey);
// Derive signing key (tweaked if UTXOs are tweaked)
const privkeyBytes = selectedTweak
? btDeriveChainedPrivkey(hexToBytes(kp.privkey), [selectedTweak])
: hexToBytes(kp.privkey);

// Generate a new keypair for the voucher recipient
const voucherPrivkey = secp256k1.utils.randomPrivateKey();
Expand Down
2 changes: 1 addition & 1 deletion src/token.js
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,7 @@ function btDeriveChainedPubkey(pubkeyBase, states) {
return cur;
}

function btDeriveChainedPrivkey(privkeyBytes, states) {
export function btDeriveChainedPrivkey(privkeyBytes, states) {
let d = bytesToBigInt(privkeyBytes);
let cur = new Uint8Array(secp256k1.getPublicKey(privkeyBytes, true));
for (const s of states) {
Expand Down