bolt: derive v2 channel ids from revocation basepoints

smite/src/bolt/types.rs

@@ -2,8 +2,9 @@
 
 use super::{FeatureBit, Features};
 use bitcoin::OutPoint;
-use bitcoin::hashes::Hash;
+use bitcoin::hashes::{Hash, sha256};
 use bitcoin::hex::DisplayHex;
+use bitcoin::secp256k1::PublicKey;
 use serde::{Deserialize, Serialize};
 use std::fmt;
 
@@ -79,6 +80,37 @@ impl ChannelId {
         res[31] ^= (outpoint.vout & 0xff) as u8;
         Self(res)
     }
+
+    /// Creates a _v2_ channel ID from both peers' revocation basepoints.
+    #[must_use]
+    pub fn v2_from_revocation_basepoints(basepoint1: &PublicKey, basepoint2: &PublicKey) -> Self {
+        Self::v2_from_serialized_basepoints(basepoint1.serialize(), basepoint2.serialize())
+    }
+
+    /// Creates a _v2_ `temporary_channel_id` from the opener's revocation
+    /// basepoint.
+    #[must_use]
+    pub fn v2_temporary_from_revocation_basepoint(
+        opener_basepoint: &PublicKey,
+    ) -> TemporaryChannelId {
+        Self::v2_from_serialized_basepoints([0u8; PUBLIC_KEY_SIZE], opener_basepoint.serialize())
+    }
+
+    /// Hashes two already-serialized basepoints in BOLT 2's canonical order.
+    fn v2_from_serialized_basepoints(
+        basepoint1: [u8; PUBLIC_KEY_SIZE],
+        basepoint2: [u8; PUBLIC_KEY_SIZE],
+    ) -> Self {
+        let (lesser, greater) = if basepoint1 <= basepoint2 {
+            (basepoint1, basepoint2)
+        } else {
+            (basepoint2, basepoint1)
+        };
+        let mut preimage = [0u8; PUBLIC_KEY_SIZE * 2];
+        preimage[..PUBLIC_KEY_SIZE].copy_from_slice(&lesser);
+        preimage[PUBLIC_KEY_SIZE..].copy_from_slice(&greater);
+        Self(sha256::Hash::hash(&preimage).to_byte_array())
+    }
 }
 
 impl fmt::Display for ChannelId {
@@ -426,6 +458,16 @@ mod tests {
     use super::*;
     use bitcoin::{OutPoint, Txid};
 
+    /// The two `funding_pubkey`s of the 2-of-2 output in the BOLT 3
+    /// "Appendix G: Dual Funded Transaction Test Vectors".
+    const BASEPOINT_1: &str = "0292edb5f7bbf9e900f7e024be1c1339c6d149c11930e613af3a983d2565f4e41e";
+    const BASEPOINT_2: &str = "02e16172a41e928cbd78f761bd1c657c4afc7495a1244f7f30166b654fbf7661e3";
+
+    fn pubkey(hex_str: &str) -> PublicKey {
+        let bytes = hex::decode(hex_str).expect("valid hex");
+        PublicKey::from_slice(&bytes).expect("valid pubkey")
+    }
+
     #[test]
     fn bigsize_new() {
         let bs = BigSize::new(42);
@@ -516,6 +558,64 @@ mod tests {
         }
     }
 
+    #[test]
+    fn channel_id_v2_hashes_sorted_basepoints() {
+        // Expected value computed by LDK's `ChannelId::v2_from_revocation_basepoints`.
+        let channel_id =
+            ChannelId::v2_from_revocation_basepoints(&pubkey(BASEPOINT_1), &pubkey(BASEPOINT_2));
+
+        assert_eq!(
+            channel_id.to_string(),
+            "59bc22f722836ce5095a37504f8ab87b1b2dbdc8aad638b77da3f5f3e8330edd",
+        );
+    }
+
+    #[test]
+    fn channel_id_v2_from_revocation_basepoints_is_order_independent() {
+        let basepoint_1 = pubkey(BASEPOINT_1);
+        let basepoint_2 = pubkey(BASEPOINT_2);
+
+        assert_eq!(
+            ChannelId::v2_from_revocation_basepoints(&basepoint_1, &basepoint_2),
+            ChannelId::v2_from_revocation_basepoints(&basepoint_2, &basepoint_1),
+        );
+    }
+
+    #[test]
+    fn channel_id_v2_temporary_hashes_zeroed_basepoint_first() {
+        // Expected values computed by LDK's `ChannelId::temporary_v2_from_revocation_basepoint`.
+        assert_eq!(
+            ChannelId::v2_temporary_from_revocation_basepoint(&pubkey(BASEPOINT_1)).to_string(),
+            "90fc2d0fcef3376e4c26de47e9c86a7362adecf87c8c1a01cdaa3263abd74c5a",
+        );
+        assert_eq!(
+            ChannelId::v2_temporary_from_revocation_basepoint(&pubkey(BASEPOINT_2)).to_string(),
+            "270d4e8fa33e0c15f46c4978186d02c51a5307229ba5689c9f600c68360e25e3",
+        );
+    }
+
+    #[test]
+    fn channel_id_v2_temporary_differs_from_final() {
+        let basepoint_1 = pubkey(BASEPOINT_1);
+        let basepoint_2 = pubkey(BASEPOINT_2);
+
+        assert_ne!(
+            ChannelId::v2_temporary_from_revocation_basepoint(&basepoint_1),
+            ChannelId::v2_from_revocation_basepoints(&basepoint_1, &basepoint_2),
+        );
+    }
+
+    #[test]
+    fn channel_id_v2_distinguishes_basepoints() {
+        let basepoint_1 = pubkey(BASEPOINT_1);
+        let basepoint_2 = pubkey(BASEPOINT_2);
+
+        assert_ne!(
+            ChannelId::v2_from_revocation_basepoints(&basepoint_1, &basepoint_1),
+            ChannelId::v2_from_revocation_basepoints(&basepoint_1, &basepoint_2),
+        );
+    }
+
     #[test]
     fn short_channel_id_ord_matches_packed_u64() {
         let a = ShortChannelId::new(100, 0, 0);