1 //! Various utilities for building scripts and deriving keys related to channels. These are
2 //! largely of interest for those implementing chain::keysinterface::ChannelKeys message signing
5 use bitcoin::blockdata::script::{Script,Builder};
6 use bitcoin::blockdata::opcodes;
7 use bitcoin::blockdata::transaction::{TxIn,TxOut,OutPoint,Transaction, SigHashType};
8 use bitcoin::consensus::encode::{self, Decodable, Encodable};
9 use bitcoin::util::bip143;
11 use bitcoin_hashes::{Hash, HashEngine};
12 use bitcoin_hashes::sha256::Hash as Sha256;
13 use bitcoin_hashes::ripemd160::Hash as Ripemd160;
14 use bitcoin_hashes::hash160::Hash as Hash160;
15 use bitcoin_hashes::sha256d::Hash as Sha256dHash;
17 use ln::channelmanager::{PaymentHash, PaymentPreimage};
18 use ln::msgs::DecodeError;
19 use util::ser::{Readable, Writeable, Writer, WriterWriteAdaptor};
21 use secp256k1::key::{SecretKey, PublicKey};
22 use secp256k1::{Secp256k1, Signature};
25 pub(super) const HTLC_SUCCESS_TX_WEIGHT: u64 = 703;
26 pub(super) const HTLC_TIMEOUT_TX_WEIGHT: u64 = 663;
28 // Various functions for key derivation and transaction creation for use within channels. Primarily
29 // used in Channel and ChannelMonitor.
31 pub(super) fn build_commitment_secret(commitment_seed: &[u8; 32], idx: u64) -> [u8; 32] {
32 let mut res: [u8; 32] = commitment_seed.clone();
35 if idx & (1 << bitpos) == (1 << bitpos) {
36 res[bitpos / 8] ^= 1 << (bitpos & 7);
37 res = Sha256::hash(&res).into_inner();
43 /// Derives a per-commitment-transaction private key (eg an htlc key or payment key) from the base
44 /// private key for that type of key and the per_commitment_point (available in TxCreationKeys)
45 pub fn derive_private_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, base_secret: &SecretKey) -> Result<SecretKey, secp256k1::Error> {
46 let mut sha = Sha256::engine();
47 sha.input(&per_commitment_point.serialize());
48 sha.input(&PublicKey::from_secret_key(&secp_ctx, &base_secret).serialize());
49 let res = Sha256::from_engine(sha).into_inner();
51 let mut key = base_secret.clone();
52 key.add_assign(&res)?;
56 pub(super) fn derive_public_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, base_point: &PublicKey) -> Result<PublicKey, secp256k1::Error> {
57 let mut sha = Sha256::engine();
58 sha.input(&per_commitment_point.serialize());
59 sha.input(&base_point.serialize());
60 let res = Sha256::from_engine(sha).into_inner();
62 let hashkey = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&res)?);
63 base_point.combine(&hashkey)
66 /// Derives a revocation key from its constituent parts.
67 /// Note that this is infallible iff we trust that at least one of the two input keys are randomly
68 /// generated (ie our own).
69 pub(super) fn derive_private_revocation_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_secret: &SecretKey, revocation_base_secret: &SecretKey) -> Result<SecretKey, secp256k1::Error> {
70 let revocation_base_point = PublicKey::from_secret_key(&secp_ctx, &revocation_base_secret);
71 let per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &per_commitment_secret);
73 let rev_append_commit_hash_key = {
74 let mut sha = Sha256::engine();
75 sha.input(&revocation_base_point.serialize());
76 sha.input(&per_commitment_point.serialize());
78 Sha256::from_engine(sha).into_inner()
80 let commit_append_rev_hash_key = {
81 let mut sha = Sha256::engine();
82 sha.input(&per_commitment_point.serialize());
83 sha.input(&revocation_base_point.serialize());
85 Sha256::from_engine(sha).into_inner()
88 let mut part_a = revocation_base_secret.clone();
89 part_a.mul_assign(&rev_append_commit_hash_key)?;
90 let mut part_b = per_commitment_secret.clone();
91 part_b.mul_assign(&commit_append_rev_hash_key)?;
92 part_a.add_assign(&part_b[..])?;
96 pub(super) fn derive_public_revocation_key<T: secp256k1::Verification>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, revocation_base_point: &PublicKey) -> Result<PublicKey, secp256k1::Error> {
97 let rev_append_commit_hash_key = {
98 let mut sha = Sha256::engine();
99 sha.input(&revocation_base_point.serialize());
100 sha.input(&per_commitment_point.serialize());
102 Sha256::from_engine(sha).into_inner()
104 let commit_append_rev_hash_key = {
105 let mut sha = Sha256::engine();
106 sha.input(&per_commitment_point.serialize());
107 sha.input(&revocation_base_point.serialize());
109 Sha256::from_engine(sha).into_inner()
112 let mut part_a = revocation_base_point.clone();
113 part_a.mul_assign(&secp_ctx, &rev_append_commit_hash_key)?;
114 let mut part_b = per_commitment_point.clone();
115 part_b.mul_assign(&secp_ctx, &commit_append_rev_hash_key)?;
116 part_a.combine(&part_b)
119 /// The set of public keys which are used in the creation of one commitment transaction.
120 /// These are derived from the channel base keys and per-commitment data.
122 pub struct TxCreationKeys {
123 /// The per-commitment public key which was used to derive the other keys.
124 pub per_commitment_point: PublicKey,
125 /// The revocation key which is used to allow the owner of the commitment transaction to
126 /// provide their counterparty the ability to punish them if they broadcast an old state.
127 pub(crate) revocation_key: PublicKey,
129 pub(crate) a_htlc_key: PublicKey,
131 pub(crate) b_htlc_key: PublicKey,
132 /// A's Payment Key (which isn't allowed to be spent from for some delay)
133 pub(crate) a_delayed_payment_key: PublicKey,
135 pub(crate) b_payment_key: PublicKey,
138 /// One counterparty's public keys which do not change over the life of a channel.
140 pub struct ChannelPublicKeys {
141 /// The public key which is used to sign all commitment transactions, as it appears in the
142 /// on-chain channel lock-in 2-of-2 multisig output.
143 pub funding_pubkey: PublicKey,
144 /// The base point which is used (with derive_public_revocation_key) to derive per-commitment
145 /// revocation keys. The per-commitment revocation private key is then revealed by the owner of
146 /// a commitment transaction so that their counterparty can claim all available funds if they
147 /// broadcast an old state.
148 pub revocation_basepoint: PublicKey,
149 /// The base point which is used (with derive_public_key) to derive a per-commitment payment
150 /// public key which receives immediately-spendable non-HTLC-encumbered funds.
151 pub payment_basepoint: PublicKey,
152 /// The base point which is used (with derive_public_key) to derive a per-commitment payment
153 /// public key which receives non-HTLC-encumbered funds which are only available for spending
154 /// after some delay (or can be claimed via the revocation path).
155 pub delayed_payment_basepoint: PublicKey,
156 /// The base point which is used (with derive_public_key) to derive a per-commitment public key
157 /// which is used to encumber HTLC-in-flight outputs.
158 pub htlc_basepoint: PublicKey,
161 impl_writeable!(ChannelPublicKeys, 33*5, {
163 revocation_basepoint,
165 delayed_payment_basepoint,
170 impl TxCreationKeys {
171 pub(crate) fn new<T: secp256k1::Signing + secp256k1::Verification>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, a_delayed_payment_base: &PublicKey, a_htlc_base: &PublicKey, b_revocation_base: &PublicKey, b_payment_base: &PublicKey, b_htlc_base: &PublicKey) -> Result<TxCreationKeys, secp256k1::Error> {
173 per_commitment_point: per_commitment_point.clone(),
174 revocation_key: derive_public_revocation_key(&secp_ctx, &per_commitment_point, &b_revocation_base)?,
175 a_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_htlc_base)?,
176 b_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_htlc_base)?,
177 a_delayed_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_delayed_payment_base)?,
178 b_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_payment_base)?,
183 /// Gets the "to_local" output redeemscript, ie the script which is time-locked or spendable by
184 /// the revocation key
185 pub(super) fn get_revokeable_redeemscript(revocation_key: &PublicKey, to_self_delay: u16, delayed_payment_key: &PublicKey) -> Script {
186 Builder::new().push_opcode(opcodes::all::OP_IF)
187 .push_slice(&revocation_key.serialize())
188 .push_opcode(opcodes::all::OP_ELSE)
189 .push_int(to_self_delay as i64)
190 .push_opcode(opcodes::all::OP_CSV)
191 .push_opcode(opcodes::all::OP_DROP)
192 .push_slice(&delayed_payment_key.serialize())
193 .push_opcode(opcodes::all::OP_ENDIF)
194 .push_opcode(opcodes::all::OP_CHECKSIG)
198 #[derive(Clone, PartialEq)]
199 /// Information about an HTLC as it appears in a commitment transaction
200 pub struct HTLCOutputInCommitment {
201 /// Whether the HTLC was "offered" (ie outbound in relation to this commitment transaction).
202 /// Note that this is not the same as whether it is ountbound *from us*. To determine that you
203 /// need to compare this value to whether the commitment transaction in question is that of
204 /// the remote party or our own.
206 /// The value, in msat, of the HTLC. The value as it appears in the commitment transaction is
207 /// this divided by 1000.
208 pub amount_msat: u64,
209 /// The CLTV lock-time at which this HTLC expires.
210 pub cltv_expiry: u32,
211 /// The hash of the preimage which unlocks this HTLC.
212 pub payment_hash: PaymentHash,
213 /// The position within the commitment transactions' outputs. This may be None if the value is
214 /// below the dust limit (in which case no output appears in the commitment transaction and the
215 /// value is spent to additional transaction fees).
216 pub transaction_output_index: Option<u32>,
220 pub(super) fn get_htlc_redeemscript_with_explicit_keys(htlc: &HTLCOutputInCommitment, a_htlc_key: &PublicKey, b_htlc_key: &PublicKey, revocation_key: &PublicKey) -> Script {
221 let payment_hash160 = Ripemd160::hash(&htlc.payment_hash.0[..]).into_inner();
223 Builder::new().push_opcode(opcodes::all::OP_DUP)
224 .push_opcode(opcodes::all::OP_HASH160)
225 .push_slice(&Hash160::hash(&revocation_key.serialize())[..])
226 .push_opcode(opcodes::all::OP_EQUAL)
227 .push_opcode(opcodes::all::OP_IF)
228 .push_opcode(opcodes::all::OP_CHECKSIG)
229 .push_opcode(opcodes::all::OP_ELSE)
230 .push_slice(&b_htlc_key.serialize()[..])
231 .push_opcode(opcodes::all::OP_SWAP)
232 .push_opcode(opcodes::all::OP_SIZE)
234 .push_opcode(opcodes::all::OP_EQUAL)
235 .push_opcode(opcodes::all::OP_NOTIF)
236 .push_opcode(opcodes::all::OP_DROP)
238 .push_opcode(opcodes::all::OP_SWAP)
239 .push_slice(&a_htlc_key.serialize()[..])
241 .push_opcode(opcodes::all::OP_CHECKMULTISIG)
242 .push_opcode(opcodes::all::OP_ELSE)
243 .push_opcode(opcodes::all::OP_HASH160)
244 .push_slice(&payment_hash160)
245 .push_opcode(opcodes::all::OP_EQUALVERIFY)
246 .push_opcode(opcodes::all::OP_CHECKSIG)
247 .push_opcode(opcodes::all::OP_ENDIF)
248 .push_opcode(opcodes::all::OP_ENDIF)
251 Builder::new().push_opcode(opcodes::all::OP_DUP)
252 .push_opcode(opcodes::all::OP_HASH160)
253 .push_slice(&Hash160::hash(&revocation_key.serialize())[..])
254 .push_opcode(opcodes::all::OP_EQUAL)
255 .push_opcode(opcodes::all::OP_IF)
256 .push_opcode(opcodes::all::OP_CHECKSIG)
257 .push_opcode(opcodes::all::OP_ELSE)
258 .push_slice(&b_htlc_key.serialize()[..])
259 .push_opcode(opcodes::all::OP_SWAP)
260 .push_opcode(opcodes::all::OP_SIZE)
262 .push_opcode(opcodes::all::OP_EQUAL)
263 .push_opcode(opcodes::all::OP_IF)
264 .push_opcode(opcodes::all::OP_HASH160)
265 .push_slice(&payment_hash160)
266 .push_opcode(opcodes::all::OP_EQUALVERIFY)
268 .push_opcode(opcodes::all::OP_SWAP)
269 .push_slice(&a_htlc_key.serialize()[..])
271 .push_opcode(opcodes::all::OP_CHECKMULTISIG)
272 .push_opcode(opcodes::all::OP_ELSE)
273 .push_opcode(opcodes::all::OP_DROP)
274 .push_int(htlc.cltv_expiry as i64)
275 .push_opcode(opcodes::all::OP_CLTV)
276 .push_opcode(opcodes::all::OP_DROP)
277 .push_opcode(opcodes::all::OP_CHECKSIG)
278 .push_opcode(opcodes::all::OP_ENDIF)
279 .push_opcode(opcodes::all::OP_ENDIF)
284 /// note here that 'a_revocation_key' is generated using b_revocation_basepoint and a's
285 /// commitment secret. 'htlc' does *not* need to have its previous_output_index filled.
287 pub fn get_htlc_redeemscript(htlc: &HTLCOutputInCommitment, keys: &TxCreationKeys) -> Script {
288 get_htlc_redeemscript_with_explicit_keys(htlc, &keys.a_htlc_key, &keys.b_htlc_key, &keys.revocation_key)
291 /// Gets the redeemscript for a funding output from the two funding public keys.
292 /// Note that the order of funding public keys does not matter.
293 pub fn make_funding_redeemscript(a: &PublicKey, b: &PublicKey) -> Script {
294 let our_funding_key = a.serialize();
295 let their_funding_key = b.serialize();
297 let builder = Builder::new().push_opcode(opcodes::all::OP_PUSHNUM_2);
298 if our_funding_key[..] < their_funding_key[..] {
299 builder.push_slice(&our_funding_key)
300 .push_slice(&their_funding_key)
302 builder.push_slice(&their_funding_key)
303 .push_slice(&our_funding_key)
304 }.push_opcode(opcodes::all::OP_PUSHNUM_2).push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script()
307 /// panics if htlc.transaction_output_index.is_none()!
308 pub fn build_htlc_transaction(prev_hash: &Sha256dHash, feerate_per_kw: u64, to_self_delay: u16, htlc: &HTLCOutputInCommitment, a_delayed_payment_key: &PublicKey, revocation_key: &PublicKey) -> Transaction {
309 let mut txins: Vec<TxIn> = Vec::new();
311 previous_output: OutPoint {
312 txid: prev_hash.clone(),
313 vout: htlc.transaction_output_index.expect("Can't build an HTLC transaction for a dust output"),
315 script_sig: Script::new(),
320 let total_fee = if htlc.offered {
321 feerate_per_kw * HTLC_TIMEOUT_TX_WEIGHT / 1000
323 feerate_per_kw * HTLC_SUCCESS_TX_WEIGHT / 1000
326 let mut txouts: Vec<TxOut> = Vec::new();
328 script_pubkey: get_revokeable_redeemscript(revocation_key, to_self_delay, a_delayed_payment_key).to_v0_p2wsh(),
329 value: htlc.amount_msat / 1000 - total_fee //TODO: BOLT 3 does not specify if we should add amount_msat before dividing or if we should divide by 1000 before subtracting (as we do here)
334 lock_time: if htlc.offered { htlc.cltv_expiry } else { 0 },
340 /// Signs a transaction created by build_htlc_transaction. If the transaction is an
341 /// HTLC-Success transaction (ie htlc.offered is false), preimage must be set!
342 pub(crate) fn sign_htlc_transaction<T: secp256k1::Signing>(tx: &mut Transaction, their_sig: &Signature, preimage: &Option<PaymentPreimage>, htlc: &HTLCOutputInCommitment, a_htlc_key: &PublicKey, b_htlc_key: &PublicKey, revocation_key: &PublicKey, per_commitment_point: &PublicKey, htlc_base_key: &SecretKey, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Script), ()> {
343 if tx.input.len() != 1 { return Err(()); }
344 if tx.input[0].witness.len() != 0 { return Err(()); }
346 let htlc_redeemscript = get_htlc_redeemscript_with_explicit_keys(&htlc, a_htlc_key, b_htlc_key, revocation_key);
348 let our_htlc_key = derive_private_key(secp_ctx, per_commitment_point, htlc_base_key).map_err(|_| ())?;
349 let sighash = hash_to_message!(&bip143::SighashComponents::new(&tx).sighash_all(&tx.input[0], &htlc_redeemscript, htlc.amount_msat / 1000)[..]);
350 let local_tx = PublicKey::from_secret_key(&secp_ctx, &our_htlc_key) == *a_htlc_key;
351 let our_sig = secp_ctx.sign(&sighash, &our_htlc_key);
353 tx.input[0].witness.push(Vec::new()); // First is the multisig dummy
355 if local_tx { // b, then a
356 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
357 tx.input[0].witness.push(our_sig.serialize_der().to_vec());
359 tx.input[0].witness.push(our_sig.serialize_der().to_vec());
360 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
362 tx.input[0].witness[1].push(SigHashType::All as u8);
363 tx.input[0].witness[2].push(SigHashType::All as u8);
366 tx.input[0].witness.push(Vec::new());
367 assert!(preimage.is_none());
369 tx.input[0].witness.push(preimage.unwrap().0.to_vec());
372 tx.input[0].witness.push(htlc_redeemscript.as_bytes().to_vec());
374 Ok((our_sig, htlc_redeemscript))
378 /// We use this to track local commitment transactions and put off signing them until we are ready
379 /// to broadcast. Eventually this will require a signer which is possibly external, but for now we
380 /// just pass in the SecretKeys required.
381 pub(crate) struct LocalCommitmentTransaction {
384 impl LocalCommitmentTransaction {
386 pub fn dummy() -> Self {
387 Self { tx: Transaction {
395 pub fn new_missing_local_sig(mut tx: Transaction, their_sig: &Signature, our_funding_key: &PublicKey, their_funding_key: &PublicKey) -> LocalCommitmentTransaction {
396 if tx.input.len() != 1 { panic!("Tried to store a commitment transaction that had input count != 1!"); }
397 if tx.input[0].witness.len() != 0 { panic!("Tried to store a signed commitment transaction?"); }
399 tx.input[0].witness.push(Vec::new()); // First is the multisig dummy
401 if our_funding_key.serialize()[..] < their_funding_key.serialize()[..] {
402 tx.input[0].witness.push(Vec::new());
403 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
404 tx.input[0].witness[2].push(SigHashType::All as u8);
406 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
407 tx.input[0].witness[1].push(SigHashType::All as u8);
408 tx.input[0].witness.push(Vec::new());
414 pub fn txid(&self) -> Sha256dHash {
418 pub fn has_local_sig(&self) -> bool {
419 if self.tx.input.len() != 1 { panic!("Commitment transactions must have input count == 1!"); }
420 if self.tx.input[0].witness.len() == 4 {
421 assert!(!self.tx.input[0].witness[1].is_empty());
422 assert!(!self.tx.input[0].witness[2].is_empty());
425 assert_eq!(self.tx.input[0].witness.len(), 3);
426 assert!(self.tx.input[0].witness[0].is_empty());
427 assert!(self.tx.input[0].witness[1].is_empty() || self.tx.input[0].witness[2].is_empty());
432 pub fn add_local_sig<T: secp256k1::Signing>(&mut self, funding_key: &SecretKey, funding_redeemscript: &Script, channel_value_satoshis: u64, secp_ctx: &Secp256k1<T>) {
433 if self.has_local_sig() { return; }
434 let sighash = hash_to_message!(&bip143::SighashComponents::new(&self.tx)
435 .sighash_all(&self.tx.input[0], funding_redeemscript, channel_value_satoshis)[..]);
436 let our_sig = secp_ctx.sign(&sighash, funding_key);
438 if self.tx.input[0].witness[1].is_empty() {
439 self.tx.input[0].witness[1] = our_sig.serialize_der().to_vec();
440 self.tx.input[0].witness[1].push(SigHashType::All as u8);
442 self.tx.input[0].witness[2] = our_sig.serialize_der().to_vec();
443 self.tx.input[0].witness[2].push(SigHashType::All as u8);
446 self.tx.input[0].witness.push(funding_redeemscript.as_bytes().to_vec());
449 pub fn without_valid_witness(&self) -> &Transaction { &self.tx }
450 pub fn with_valid_witness(&self) -> &Transaction {
451 assert!(self.has_local_sig());
455 impl PartialEq for LocalCommitmentTransaction {
456 // We dont care whether we are signed in equality comparison
457 fn eq(&self, o: &Self) -> bool {
458 self.txid() == o.txid()
461 impl Writeable for LocalCommitmentTransaction {
462 fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
463 if let Err(e) = self.tx.consensus_encode(&mut WriterWriteAdaptor(writer)) {
465 encode::Error::Io(e) => return Err(e),
466 _ => panic!("local tx must have been well-formed!"),
472 impl<R: ::std::io::Read> Readable<R> for LocalCommitmentTransaction {
473 fn read(reader: &mut R) -> Result<Self, DecodeError> {
474 let tx = match Transaction::consensus_decode(reader.by_ref()) {
477 encode::Error::Io(ioe) => return Err(DecodeError::Io(ioe)),
478 _ => return Err(DecodeError::InvalidValue),
482 if tx.input.len() != 1 {
483 // Ensure tx didn't hit the 0-input ambiguity case.
484 return Err(DecodeError::InvalidValue);