Merge pull request #3004 from TheBlueMatt/2024-04-2761-followups

[rust-lightning] / lightning / src / ln / channel_keys.rs

diff --git a/lightning/src/ln/channel_keys.rs b/lightning/src/ln/channel_keys.rs
index 423d410740720dc2bb5b4e12aa39cf5d1bf4c2ca..9e839b15e3c40636c72553b32c9eb52f35079f7b 100644 (file)
--- a/lightning/src/ln/channel_keys.rs
+++ b/lightning/src/ln/channel_keys.rs
@@ -31,26 +31,30 @@ macro_rules! doc_comment {
        };
 }
 macro_rules! basepoint_impl {
-       ($BasepointT:ty) => {
+       ($BasepointT:ty $(, $KeyName: expr)?) => {
                impl $BasepointT {
                        /// Get inner Public Key
                        pub fn to_public_key(&self) -> PublicKey {
                                self.0
                        }
 
-                       /// Derives a per-commitment-transaction (eg an htlc key or delayed_payment key) private key addition tweak
-                       /// from a basepoint and a per_commitment_point:
-                       /// `privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`
-                       /// This calculates the hash part in the tweak derivation process, which is used to ensure
-                       /// that each key is unique and cannot be guessed by an external party. It is equivalent
-                       /// to the `from_basepoint` method, but without the addition operation, providing just the
-                       /// tweak from the hash of the per_commitment_point and the basepoint.
-                       pub fn derive_add_tweak(&self, per_commitment_point: &PublicKey) -> [u8; 32] {
-                               let mut sha = Sha256::engine();
-                               sha.input(&per_commitment_point.serialize());
-                               sha.input(&self.to_public_key().serialize());
-                               Sha256::from_engine(sha).to_byte_array()
-                       }
+                       $(doc_comment!(
+                               concat!(
+                               "Derives the \"tweak\" used in calculate [`", $KeyName, "::from_basepoint`].\n",
+                               "\n",
+                               "[`", $KeyName, "::from_basepoint`] calculates a private key as:\n",
+                               "`privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`\n",
+                               "\n",
+                               "This calculates the hash part in the tweak derivation process, which is used to\n",
+                               "ensure that each key is unique and cannot be guessed by an external party."
+                               ),
+                               pub fn derive_add_tweak(&self, per_commitment_point: &PublicKey) -> Sha256 {
+                                       let mut sha = Sha256::engine();
+                                       sha.input(&per_commitment_point.serialize());
+                                       sha.input(&self.to_public_key().serialize());
+                                       Sha256::from_engine(sha)
+                               });
+                       )?
                }
 
                impl From<PublicKey> for $BasepointT {
@@ -110,7 +114,7 @@ macro_rules! key_read_write {
 /// state broadcasted was previously revoked.
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 pub struct DelayedPaymentBasepoint(pub PublicKey);
-basepoint_impl!(DelayedPaymentBasepoint);
+basepoint_impl!(DelayedPaymentBasepoint, "DelayedPaymentKey");
 key_read_write!(DelayedPaymentBasepoint);
 
 /// A derived key built from a [`DelayedPaymentBasepoint`] and `per_commitment_point`.
@@ -137,7 +141,7 @@ key_read_write!(DelayedPaymentKey);
 /// Thus, both channel counterparties' HTLC keys will appears in each HTLC output's script.
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 pub struct HtlcBasepoint(pub PublicKey);
-basepoint_impl!(HtlcBasepoint);
+basepoint_impl!(HtlcBasepoint, "HtlcKey");
 key_read_write!(HtlcBasepoint);
 
 /// A derived key built from a [`HtlcBasepoint`] and `per_commitment_point`.
@@ -166,18 +170,20 @@ fn derive_public_key<T: secp256k1::Signing>(
        let mut sha = Sha256::engine();
        sha.input(&per_commitment_point.serialize());
        sha.input(&base_point.serialize());
-       let res = Sha256::from_engine(sha).to_byte_array();
+       let res = Sha256::from_engine(sha);
 
        add_public_key_tweak(secp_ctx, base_point, &res)
 }
 
 /// Adds a tweak to a public key to derive a new public key.
+///
+/// May panic if `tweak` is not the output of a SHA-256 hash.
 pub fn add_public_key_tweak<T: secp256k1::Signing>(
-       secp_ctx: &Secp256k1<T>, base_point: &PublicKey, tweak: &[u8; 32],
+       secp_ctx: &Secp256k1<T>, base_point: &PublicKey, tweak: &Sha256,
 ) -> PublicKey {
        let hashkey = PublicKey::from_secret_key(
                &secp_ctx,
-               &SecretKey::from_slice(tweak)
+               &SecretKey::from_slice(tweak.as_byte_array())
                        .expect("Hashes should always be valid keys unless SHA-256 is broken"),
        );
        base_point.combine(&hashkey)