_ Git - rust-lightning/blob - lightning/src/ln/channel_keys.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
   5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
   7 // You may not use this file except in accordance with one or both of these
   8 // licenses.
   9
  10 //! Keys used to generate commitment transactions.
  11 //! See: <https://github.com/lightning/bolts/blob/master/03-transactions.md#keys>
  12
  13 use bitcoin::hashes::Hash;
  14 use bitcoin::hashes::HashEngine;
  15 use bitcoin::secp256k1::Scalar;
  16 use bitcoin::secp256k1::SecretKey;
  17 use bitcoin::secp256k1::Secp256k1;
  18 use bitcoin::secp256k1;
  19 use crate::ln::msgs::DecodeError;
  20 use crate::util::ser::Readable;
  21 use crate::io;
  22 use crate::util::ser::Writer;
  23 use crate::util::ser::Writeable;
  24 use bitcoin::secp256k1::PublicKey;
  25 use bitcoin::hashes::sha256::Hash as Sha256;
  26
  27 macro_rules! doc_comment {
  28         ($x:expr, $($tt:tt)*) => {
  29                 #[doc = $x]
  30                 $($tt)*
  31         };
  32 }
  33 macro_rules! basepoint_impl {
  34         ($BasepointT:ty) => {
  35                 impl $BasepointT {
  36                         /// Get inner Public Key
  37                         pub fn to_public_key(&self) -> PublicKey {
  38                                 self.0
  39                         }
  40                 }
  41
  42                 impl From<PublicKey> for $BasepointT {
  43                         fn from(value: PublicKey) -> Self {
  44                                 Self(value)
  45                         }
  46                 }
  47
  48         }
  49 }
  50 macro_rules! key_impl {
  51         ($BasepointT:ty, $KeyName:expr) => {
  52                 doc_comment! {
  53                         concat!("Derive a public ", $KeyName, " using one node's `per_commitment_point` and its countersignatory's `basepoint`"),
  54                         pub fn from_basepoint<T: secp256k1::Signing>(
  55                                 secp_ctx: &Secp256k1<T>,
  56                                 countersignatory_basepoint: &$BasepointT,
  57                                 per_commitment_point: &PublicKey,
  58                         ) -> Self {
  59                                 Self(derive_public_key(secp_ctx, per_commitment_point, &countersignatory_basepoint.0))
  60                         }
  61                 }
  62
  63                 doc_comment! {
  64                         concat!("Build a ", $KeyName, " directly from an already-derived private key"),
  65                         pub fn from_secret_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, sk: &SecretKey) -> Self {
  66                                 Self(PublicKey::from_secret_key(&secp_ctx, &sk))
  67                         }
  68                 }
  69
  70                 /// Get inner Public Key
  71                 pub fn to_public_key(&self) -> PublicKey {
  72                         self.0
  73                 }
  74         }
  75 }
  76 macro_rules! key_read_write {
  77         ($SelfT:ty) => {
  78                 impl Writeable for $SelfT {
  79                         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
  80                                 self.0.serialize().write(w)
  81                         }
  82                 }
  83
  84                 impl Readable for $SelfT {
  85                         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
  86                                 let key: PublicKey = Readable::read(r)?;
  87                                 Ok(Self(key))
  88                         }
  89                 }
  90         }
  91 }
  92
  93
  94
  95 /// Base key used in conjunction with a `per_commitment_point` to generate a [`DelayedPaymentKey`].
  96 ///
  97 /// The delayed payment key is used to pay the commitment state broadcaster their
  98 /// non-HTLC-encumbered funds after a delay to give their counterparty a chance to punish if the
  99 /// state broadcasted was previously revoked.
 100 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 101 pub struct DelayedPaymentBasepoint(pub PublicKey);
 102 basepoint_impl!(DelayedPaymentBasepoint);
 103 key_read_write!(DelayedPaymentBasepoint);
 104
 105
 106 /// A derived key built from a [`DelayedPaymentBasepoint`] and `per_commitment_point`.
 107 ///
 108 /// The delayed payment key is used to pay the commitment state broadcaster their
 109 /// non-HTLC-encumbered funds after a delay. This delay gives their counterparty a chance to
 110 /// punish and claim all the channel funds if the state broadcasted was previously revoked.
 111 ///
 112 /// [See the BOLT specs]
 113 /// (https://github.com/lightning/bolts/blob/master/03-transactions.md#localpubkey-local_htlcpubkey-remote_htlcpubkey-local_delayedpubkey-and-remote_delayedpubkey-derivation)
 114 /// for more information on key derivation details.
 115 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 116 pub struct DelayedPaymentKey(pub PublicKey);
 117
 118 impl DelayedPaymentKey {
 119         key_impl!(DelayedPaymentBasepoint, "delayedpubkey");
 120 }
 121 key_read_write!(DelayedPaymentKey);
 122
 123 /// Base key used in conjunction with a `per_commitment_point` to generate an [`HtlcKey`].
 124 ///
 125 /// HTLC keys are used to ensure only the recipient of an HTLC can claim it on-chain with the HTLC
 126 /// preimage and that only the sender of an HTLC can claim it on-chain after it has timed out.
 127 /// Thus, both channel counterparties' HTLC keys will appears in each HTLC output's script.
 128 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 129 pub struct HtlcBasepoint(pub PublicKey);
 130 basepoint_impl!(HtlcBasepoint);
 131 key_read_write!(HtlcBasepoint);
 132
 133 /// A derived key built from a [`HtlcBasepoint`] and `per_commitment_point`.
 134 ///
 135 /// HTLC keys are used to ensure only the recipient of an HTLC can claim it on-chain with the HTLC
 136 /// preimage and that only the sender of an HTLC can claim it on-chain after it has timed out.
 137 /// Thus, both channel counterparties' HTLC keys will appears in each HTLC output's script.
 138 ///
 139 /// [See the BOLT specs]
 140 /// (https://github.com/lightning/bolts/blob/master/03-transactions.md#localpubkey-local_htlcpubkey-remote_htlcpubkey-local_delayedpubkey-and-remote_delayedpubkey-derivation)
 141 /// for more information on key derivation details.
 142 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 143 pub struct HtlcKey(pub PublicKey);
 144
 145 impl HtlcKey {
 146         key_impl!(HtlcBasepoint, "htlcpubkey");
 147 }
 148 key_read_write!(HtlcKey);
 149
 150 /// Derives a per-commitment-transaction public key (eg an htlc key or a delayed_payment key)
 151 /// from the base point and the per_commitment_key. This is the public equivalent of
 152 /// derive_private_key - using only public keys to derive a public key instead of private keys.
 153 fn derive_public_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, base_point: &PublicKey) -> PublicKey {
 154         let mut sha = Sha256::engine();
 155         sha.input(&per_commitment_point.serialize());
 156         sha.input(&base_point.serialize());
 157         let res = Sha256::from_engine(sha).to_byte_array();
 158
 159         let hashkey = PublicKey::from_secret_key(&secp_ctx,
 160                 &SecretKey::from_slice(&res).expect("Hashes should always be valid keys unless SHA-256 is broken"));
 161         base_point.combine(&hashkey)
 162                 .expect("Addition only fails if the tweak is the inverse of the key. This is not possible when the tweak contains the hash of the key.")
 163 }
 164
 165 /// Master key used in conjunction with per_commitment_point to generate [htlcpubkey](https://github.com/lightning/bolts/blob/master/03-transactions.md#key-derivation) for the latest state of a channel.
 166 /// A watcher can be given a [RevocationBasepoint] to generate per commitment [RevocationKey] to create justice transactions.
 167 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 168 pub struct RevocationBasepoint(pub PublicKey);
 169 basepoint_impl!(RevocationBasepoint);
 170 key_read_write!(RevocationBasepoint);
 171
 172
 173 /// The revocation key is used to allow a channel party to revoke their state - giving their
 174 /// counterparty the required material to claim all of their funds if they broadcast that state.
 175 ///
 176 /// Each commitment transaction has a revocation key based on the basepoint and
 177 /// per_commitment_point which is used in both commitment and HTLC transactions.
 178 ///
 179 /// See [the BOLT spec for derivation details]
 180 /// (https://github.com/lightning/bolts/blob/master/03-transactions.md#revocationpubkey-derivation)
 181 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 182 pub struct RevocationKey(pub PublicKey);
 183
 184 impl RevocationKey {
 185         /// Derives a per-commitment-transaction revocation public key from one party's per-commitment
 186         /// point and the other party's [`RevocationBasepoint`]. This is the public equivalent of
 187         /// [`chan_utils::derive_private_revocation_key`] - using only public keys to derive a public
 188         /// key instead of private keys.
 189         ///
 190         /// Note that this is infallible iff we trust that at least one of the two input keys are randomly
 191         /// generated (ie our own).
 192         ///
 193         /// [`chan_utils::derive_private_revocation_key`]: crate::ln::chan_utils::derive_private_revocation_key
 194         pub fn from_basepoint<T: secp256k1::Verification>(
 195                 secp_ctx: &Secp256k1<T>,
 196                 countersignatory_basepoint: &RevocationBasepoint,
 197                 per_commitment_point: &PublicKey,
 198         ) -> Self {
 199                 let rev_append_commit_hash_key = {
 200                         let mut sha = Sha256::engine();
 201                         sha.input(&countersignatory_basepoint.to_public_key().serialize());
 202                         sha.input(&per_commitment_point.serialize());
 203
 204                         Sha256::from_engine(sha).to_byte_array()
 205                 };
 206                 let commit_append_rev_hash_key = {
 207                         let mut sha = Sha256::engine();
 208                         sha.input(&per_commitment_point.serialize());
 209                         sha.input(&countersignatory_basepoint.to_public_key().serialize());
 210
 211                         Sha256::from_engine(sha).to_byte_array()
 212                 };
 213
 214                 let countersignatory_contrib = countersignatory_basepoint.to_public_key().mul_tweak(&secp_ctx, &Scalar::from_be_bytes(rev_append_commit_hash_key).unwrap())
 215                         .expect("Multiplying a valid public key by a hash is expected to never fail per secp256k1 docs");
 216                 let broadcaster_contrib = (&per_commitment_point).mul_tweak(&secp_ctx, &Scalar::from_be_bytes(commit_append_rev_hash_key).unwrap())
 217                         .expect("Multiplying a valid public key by a hash is expected to never fail per secp256k1 docs");
 218                 let pk = countersignatory_contrib.combine(&broadcaster_contrib)
 219                         .expect("Addition only fails if the tweak is the inverse of the key. This is not possible when the tweak commits to the key.");
 220                 Self(pk)
 221         }
 222
 223         /// Get inner Public Key
 224         pub fn to_public_key(&self) -> PublicKey {
 225                 self.0
 226         }
 227 }
 228 key_read_write!(RevocationKey);
 229
 230
 231 #[cfg(test)]
 232 mod test {
 233         use bitcoin::secp256k1::{Secp256k1, SecretKey, PublicKey};
 234         use bitcoin::hashes::hex::FromHex;
 235         use super::derive_public_key;
 236
 237         #[test]
 238         fn test_key_derivation() {
 239                 // Test vectors from BOLT 3 Appendix E:
 240                 let secp_ctx = Secp256k1::new();
 241
 242                 let base_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f").unwrap()[..]).unwrap();
 243                 let per_commitment_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("1f1e1d1c1b1a191817161514131211100f0e0d0c0b0a09080706050403020100").unwrap()[..]).unwrap();
 244
 245                 let base_point = PublicKey::from_secret_key(&secp_ctx, &base_secret);
 246                 assert_eq!(base_point.serialize()[..], <Vec<u8>>::from_hex("036d6caac248af96f6afa7f904f550253a0f3ef3f5aa2fe6838a95b216691468e2").unwrap()[..]);
 247
 248                 let per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &per_commitment_secret);
 249                 assert_eq!(per_commitment_point.serialize()[..], <Vec<u8>>::from_hex("025f7117a78150fe2ef97db7cfc83bd57b2e2c0d0dd25eaf467a4a1c2a45ce1486").unwrap()[..]);
 250
 251                 assert_eq!(derive_public_key(&secp_ctx, &per_commitment_point, &base_point).serialize()[..],
 252                         <Vec<u8>>::from_hex("0235f2dbfaa89b57ec7b055afe29849ef7ddfeb1cefdb9ebdc43f5494984db29e5").unwrap()[..]);
 253         }
 254 }