use bitcoin::blockdata::script::{Script,Builder}; use bitcoin::blockdata::opcodes; use bitcoin::blockdata::transaction::{TxIn,TxOut,OutPoint,Transaction}; use bitcoin_hashes::{Hash, HashEngine}; use bitcoin_hashes::sha256::Hash as Sha256; use bitcoin_hashes::ripemd160::Hash as Ripemd160; use bitcoin_hashes::hash160::Hash as Hash160; use bitcoin_hashes::sha256d::Hash as Sha256dHash; use ln::channelmanager::PaymentHash; use secp256k1::key::{PublicKey,SecretKey}; use secp256k1::Secp256k1; use secp256k1; pub const HTLC_SUCCESS_TX_WEIGHT: u64 = 703; pub const HTLC_TIMEOUT_TX_WEIGHT: u64 = 663; // Various functions for key derivation and transaction creation for use within channels. Primarily // used in Channel and ChannelMonitor. pub fn build_commitment_secret(commitment_seed: [u8; 32], idx: u64) -> [u8; 32] { let mut res: [u8; 32] = commitment_seed; for i in 0..48 { let bitpos = 47 - i; if idx & (1 << bitpos) == (1 << bitpos) { res[bitpos / 8] ^= 1 << (bitpos & 7); res = Sha256::hash(&res).into_inner(); } } res } pub fn derive_private_key(secp_ctx: &Secp256k1, per_commitment_point: &PublicKey, base_secret: &SecretKey) -> Result { let mut sha = Sha256::engine(); sha.input(&per_commitment_point.serialize()); sha.input(&PublicKey::from_secret_key(&secp_ctx, &base_secret).serialize()); let res = Sha256::from_engine(sha).into_inner(); let mut key = base_secret.clone(); key.add_assign(&res)?; Ok(key) } pub fn derive_public_key(secp_ctx: &Secp256k1, per_commitment_point: &PublicKey, base_point: &PublicKey) -> Result { let mut sha = Sha256::engine(); sha.input(&per_commitment_point.serialize()); sha.input(&base_point.serialize()); let res = Sha256::from_engine(sha).into_inner(); let hashkey = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&res)?); base_point.combine(&hashkey) } /// Derives a revocation key from its constituent parts pub fn derive_private_revocation_key(secp_ctx: &Secp256k1, per_commitment_secret: &SecretKey, revocation_base_secret: &SecretKey) -> Result { let revocation_base_point = PublicKey::from_secret_key(&secp_ctx, &revocation_base_secret); let per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &per_commitment_secret); let rev_append_commit_hash_key = { let mut sha = Sha256::engine(); sha.input(&revocation_base_point.serialize()); sha.input(&per_commitment_point.serialize()); Sha256::from_engine(sha).into_inner() }; let commit_append_rev_hash_key = { let mut sha = Sha256::engine(); sha.input(&per_commitment_point.serialize()); sha.input(&revocation_base_point.serialize()); Sha256::from_engine(sha).into_inner() }; let mut part_a = revocation_base_secret.clone(); part_a.mul_assign(&rev_append_commit_hash_key)?; let mut part_b = per_commitment_secret.clone(); part_b.mul_assign(&commit_append_rev_hash_key)?; part_a.add_assign(&part_b[..])?; Ok(part_a) } pub fn derive_public_revocation_key(secp_ctx: &Secp256k1, per_commitment_point: &PublicKey, revocation_base_point: &PublicKey) -> Result { let rev_append_commit_hash_key = { let mut sha = Sha256::engine(); sha.input(&revocation_base_point.serialize()); sha.input(&per_commitment_point.serialize()); Sha256::from_engine(sha).into_inner() }; let commit_append_rev_hash_key = { let mut sha = Sha256::engine(); sha.input(&per_commitment_point.serialize()); sha.input(&revocation_base_point.serialize()); Sha256::from_engine(sha).into_inner() }; let mut part_a = revocation_base_point.clone(); part_a.mul_assign(&secp_ctx, &rev_append_commit_hash_key)?; let mut part_b = per_commitment_point.clone(); part_b.mul_assign(&secp_ctx, &commit_append_rev_hash_key)?; part_a.combine(&part_b) } pub struct TxCreationKeys { pub per_commitment_point: PublicKey, pub revocation_key: PublicKey, pub a_htlc_key: PublicKey, pub b_htlc_key: PublicKey, pub a_delayed_payment_key: PublicKey, pub b_payment_key: PublicKey, } impl TxCreationKeys { pub fn new(secp_ctx: &Secp256k1, 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 { Ok(TxCreationKeys { per_commitment_point: per_commitment_point.clone(), revocation_key: derive_public_revocation_key(&secp_ctx, &per_commitment_point, &b_revocation_base)?, a_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_htlc_base)?, b_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_htlc_base)?, a_delayed_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_delayed_payment_base)?, b_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_payment_base)?, }) } } /// Gets the "to_local" output redeemscript, ie the script which is time-locked or spendable by /// the revocation key pub fn get_revokeable_redeemscript(revocation_key: &PublicKey, to_self_delay: u16, delayed_payment_key: &PublicKey) -> Script { Builder::new().push_opcode(opcodes::all::OP_IF) .push_slice(&revocation_key.serialize()) .push_opcode(opcodes::all::OP_ELSE) .push_int(to_self_delay as i64) .push_opcode(opcodes::OP_CSV) .push_opcode(opcodes::all::OP_DROP) .push_slice(&delayed_payment_key.serialize()) .push_opcode(opcodes::all::OP_ENDIF) .push_opcode(opcodes::all::OP_CHECKSIG) .into_script() } #[derive(Clone, PartialEq)] pub struct HTLCOutputInCommitment { pub offered: bool, pub amount_msat: u64, pub cltv_expiry: u32, pub payment_hash: PaymentHash, pub transaction_output_index: Option, } #[inline] pub fn get_htlc_redeemscript_with_explicit_keys(htlc: &HTLCOutputInCommitment, a_htlc_key: &PublicKey, b_htlc_key: &PublicKey, revocation_key: &PublicKey) -> Script { let payment_hash160 = Ripemd160::hash(&htlc.payment_hash.0[..]).into_inner(); if htlc.offered { Builder::new().push_opcode(opcodes::all::OP_DUP) .push_opcode(opcodes::all::OP_HASH160) .push_slice(&Hash160::hash(&revocation_key.serialize())[..]) .push_opcode(opcodes::all::OP_EQUAL) .push_opcode(opcodes::all::OP_IF) .push_opcode(opcodes::all::OP_CHECKSIG) .push_opcode(opcodes::all::OP_ELSE) .push_slice(&b_htlc_key.serialize()[..]) .push_opcode(opcodes::all::OP_SWAP) .push_opcode(opcodes::all::OP_SIZE) .push_int(32) .push_opcode(opcodes::all::OP_EQUAL) .push_opcode(opcodes::all::OP_NOTIF) .push_opcode(opcodes::all::OP_DROP) .push_int(2) .push_opcode(opcodes::all::OP_SWAP) .push_slice(&a_htlc_key.serialize()[..]) .push_int(2) .push_opcode(opcodes::all::OP_CHECKMULTISIG) .push_opcode(opcodes::all::OP_ELSE) .push_opcode(opcodes::all::OP_HASH160) .push_slice(&payment_hash160) .push_opcode(opcodes::all::OP_EQUALVERIFY) .push_opcode(opcodes::all::OP_CHECKSIG) .push_opcode(opcodes::all::OP_ENDIF) .push_opcode(opcodes::all::OP_ENDIF) .into_script() } else { Builder::new().push_opcode(opcodes::all::OP_DUP) .push_opcode(opcodes::all::OP_HASH160) .push_slice(&Hash160::hash(&revocation_key.serialize())[..]) .push_opcode(opcodes::all::OP_EQUAL) .push_opcode(opcodes::all::OP_IF) .push_opcode(opcodes::all::OP_CHECKSIG) .push_opcode(opcodes::all::OP_ELSE) .push_slice(&b_htlc_key.serialize()[..]) .push_opcode(opcodes::all::OP_SWAP) .push_opcode(opcodes::all::OP_SIZE) .push_int(32) .push_opcode(opcodes::all::OP_EQUAL) .push_opcode(opcodes::all::OP_IF) .push_opcode(opcodes::all::OP_HASH160) .push_slice(&payment_hash160) .push_opcode(opcodes::all::OP_EQUALVERIFY) .push_int(2) .push_opcode(opcodes::all::OP_SWAP) .push_slice(&a_htlc_key.serialize()[..]) .push_int(2) .push_opcode(opcodes::all::OP_CHECKMULTISIG) .push_opcode(opcodes::all::OP_ELSE) .push_opcode(opcodes::all::OP_DROP) .push_int(htlc.cltv_expiry as i64) .push_opcode(opcodes::OP_CLTV) .push_opcode(opcodes::all::OP_DROP) .push_opcode(opcodes::all::OP_CHECKSIG) .push_opcode(opcodes::all::OP_ENDIF) .push_opcode(opcodes::all::OP_ENDIF) .into_script() } } /// note here that 'a_revocation_key' is generated using b_revocation_basepoint and a's /// commitment secret. 'htlc' does *not* need to have its previous_output_index filled. #[inline] pub fn get_htlc_redeemscript(htlc: &HTLCOutputInCommitment, keys: &TxCreationKeys) -> Script { get_htlc_redeemscript_with_explicit_keys(htlc, &keys.a_htlc_key, &keys.b_htlc_key, &keys.revocation_key) } /// panics if htlc.transaction_output_index.is_none()! 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 { let mut txins: Vec = Vec::new(); txins.push(TxIn { previous_output: OutPoint { txid: prev_hash.clone(), vout: htlc.transaction_output_index.expect("Can't build an HTLC transaction for a dust output"), }, script_sig: Script::new(), sequence: 0, witness: Vec::new(), }); let total_fee = if htlc.offered { feerate_per_kw * HTLC_TIMEOUT_TX_WEIGHT / 1000 } else { feerate_per_kw * HTLC_SUCCESS_TX_WEIGHT / 1000 }; let mut txouts: Vec = Vec::new(); txouts.push(TxOut { script_pubkey: get_revokeable_redeemscript(revocation_key, to_self_delay, a_delayed_payment_key).to_v0_p2wsh(), 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) }); Transaction { version: 2, lock_time: if htlc.offered { htlc.cltv_expiry } else { 0 }, input: txins, output: txouts, } }