From 1b28375658d2016ea072a10b10fbebc362fa8514 Mon Sep 17 00:00:00 2001
From: Dr Maxim Orlovsky <orlovsky@pandoracore.com>
Date: Thu, 31 Mar 2022 15:16:39 +0200
Subject: [PATCH 1/2] Abstract tap branch hash computing into a dedicated
 method

---
 src/util/taproot.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/util/taproot.rs b/src/util/taproot.rs
index 69d381b7..d4f5f9dd 100644
--- a/src/util/taproot.rs
+++ b/src/util/taproot.rs
@@ -131,6 +131,21 @@ impl TapLeafHash {
     }
 }
 
+impl TapBranchHash {
+    /// Computes branch hash given two hashes of the nodes underneath it.
+    pub fn from_node_hashes(a: sha256::Hash, b: sha256::Hash) -> TapBranchHash {
+        let mut eng = TapBranchHash::engine();
+        if a < b {
+            eng.input(&a);
+            eng.input(&b);
+        } else {
+            eng.input(&b);
+            eng.input(&a);
+        };
+        TapBranchHash::from_engine(eng)
+    }
+}
+
 /// Maximum depth of a taproot tree script spend path.
 // https://github.com/bitcoin/bitcoin/blob/e826b22da252e0599c61d21c98ff89f366b3120f/src/script/interpreter.h#L229
 pub const TAPROOT_CONTROL_MAX_NODE_COUNT: usize = 128;

From f3ebfd6f8b049a2e2cfe6e9bd2b1b2f788b98d48 Mon Sep 17 00:00:00 2001
From: Dr Maxim Orlovsky <orlovsky@pandoracore.com>
Date: Thu, 31 Mar 2022 15:21:36 +0200
Subject: [PATCH 2/2] Remove repeated tap branch hash computing logic

---
 src/util/taproot.rs | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

diff --git a/src/util/taproot.rs b/src/util/taproot.rs
index d4f5f9dd..bc5794fd 100644
--- a/src/util/taproot.rs
+++ b/src/util/taproot.rs
@@ -576,16 +576,9 @@ impl NodeInfo {
             b_leaf.merkle_branch.push(a.hash)?; // add hashing partner
             all_leaves.push(b_leaf);
         }
-        let mut eng = TapBranchHash::engine();
-        if a.hash < b.hash {
-            eng.input(&a.hash);
-            eng.input(&b.hash);
-        } else {
-            eng.input(&b.hash);
-            eng.input(&a.hash);
-        };
+        let hash = TapBranchHash::from_node_hashes(a.hash, b.hash);
         Ok(Self {
-            hash: sha256::Hash::from_engine(eng),
+            hash: sha256::Hash::from_inner(hash.into_inner()),
             leaves: all_leaves,
         })
     }
@@ -790,16 +783,11 @@ impl ControlBlock {
         let mut curr_hash = TapBranchHash::from_inner(leaf_hash.into_inner());
         // Verify the proof
         for elem in self.merkle_branch.as_inner() {
-            let mut eng = TapBranchHash::engine();
-            if curr_hash.as_inner() < elem.as_inner() {
-                eng.input(&curr_hash);
-                eng.input(elem);
-            } else {
-                eng.input(elem);
-                eng.input(&curr_hash);
-            }
             // Recalculate the curr hash as parent hash
-            curr_hash = TapBranchHash::from_engine(eng);
+            curr_hash = TapBranchHash::from_node_hashes(
+                sha256::Hash::from_inner(curr_hash.into_inner()),
+                *elem
+            );
         }
         // compute the taptweak
         let tweak = TapTweakHash::from_key_and_tweak(self.internal_key, Some(curr_hash));