Merge rust-bitcoin/rust-bitcoin#707: P2tr fixes

e4774e74eb fixups to taptweaking code (sanket1729)

Pull request description:

  This was my bad for not clearly stating the expected spec #687 . Changed values to references so that we only take ownership where it is required.

  This should simplify the #697

ACKs for top commit:
  Kixunil:
    ACK e4774e74eb
  dr-orlovsky:
    utACK e4774e74eb

Tree-SHA512: adacbfa8a77f46b2c85720f3760ed12a437f40d8422731d0207662d7947c95dda79d576923f6056c77f57977a3dcd25afd270f0ee11e9c3be9d067ccdc63371a

src/util/address.rs

@@ -514,9 +514,9 @@ impl Address {
 
     /// Create a pay to taproot address from untweaked key
     pub fn p2tr<C: Verification>(
-        secp: Secp256k1<C>,
+        secp: &Secp256k1<C>,
         internal_key: UntweakedPublicKey,
-        merkle_root: Option<TapBranchHash>,
+        merkle_root: Option<&TapBranchHash>,
         network: Network
     ) -> Address {
         Address {
@@ -539,7 +539,7 @@ impl Address {
             network: network,
             payload: Payload::WitnessProgram {
                 version: WitnessVersion::V1,
-                program: output_key.into_inner().serialize().to_vec()
+                program: output_key.as_inner().serialize().to_vec()
             }
         }
     }
@@ -1196,7 +1196,8 @@ mod tests {
     fn p2tr_from_untweaked(){
         //Test case from BIP-086
         let internal_key = schnorrsig::PublicKey::from_str("cc8a4bc64d897bddc5fbc2f670f7a8ba0b386779106cf1223c6fc5d7cd6fc115").unwrap();
-        let address = Address::p2tr(Secp256k1::new(), internal_key,None, Network::Bitcoin);
+        let secp = Secp256k1::verification_only();
+        let address = Address::p2tr(&secp, internal_key, None, Network::Bitcoin);
         assert_eq!(address.to_string(), "bc1p5cyxnuxmeuwuvkwfem96lqzszd02n6xdcjrs20cac6yqjjwudpxqkedrcr");
         assert_eq!(address.address_type(), Some(AddressType::P2tr));
         roundtrips(&address);

src/util/schnorr.rs

@@ -31,30 +31,29 @@ pub struct TweakedPublicKey(PublicKey);
 /// A trait for tweaking Schnorr public keys
 pub trait TapTweak {
     /// Tweaks an untweaked public key given an untweaked key and optional script tree merkle root.
-    /// 
-    /// This is done by using the equation Q = P + H(P|c)G, where 
+    ///
+    /// This is done by using the equation Q = P + H(P|c)G, where
     ///  * Q is the tweaked key
     ///  * P is the internal key
     ///  * H is the hash function
     ///  * c is the commitment data
     ///  * G is the generator point
-    fn tap_tweak<C: Verification>(&self, secp: Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> TweakedPublicKey;
+    fn tap_tweak<C: Verification>(&self, secp: &Secp256k1<C>, merkle_root: Option<&TapBranchHash>) -> TweakedPublicKey;
 
     /// Directly convert an UntweakedPublicKey to a TweakedPublicKey
-    /// 
+    ///
     /// This method is dangerous and can lead to loss of funds if used incorrectly.
     /// Specifically, in multi-party protocols a peer can provide a value that allows them to steal.
     fn dangerous_assume_tweaked(self) -> TweakedPublicKey;
 }
 
 impl TapTweak for UntweakedPublicKey {
-    fn tap_tweak<C: Verification>(&self, secp: Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> TweakedPublicKey {
+    fn tap_tweak<C: Verification>(&self, secp: &Secp256k1<C>, merkle_root: Option<&TapBranchHash>) -> TweakedPublicKey {
         // Compute the tweak
         let mut engine = TapTweakHash::engine();
         engine.input(&self.serialize());
         merkle_root.map(|hash| engine.input(&hash));
         let tweak_value: [u8; 32] = TapTweakHash::from_engine(engine).into_inner();
-            
 
         //Tweak the internal key by the tweak value
         let mut output_key = self.clone();
@@ -64,7 +63,6 @@ impl TapTweak for UntweakedPublicKey {
         } else { unreachable!("Tap tweak failed") }
     }
 
-    
     fn dangerous_assume_tweaked(self) -> TweakedPublicKey {
         TweakedPublicKey(self)
     }
@@ -76,9 +74,15 @@ impl TweakedPublicKey {
     pub fn new(key: PublicKey) -> TweakedPublicKey {
         TweakedPublicKey(key)
     }
-    
-    /// Returns the underlying public key 
+
+    /// Returns the underlying public key
     pub fn into_inner(self) -> PublicKey {
         self.0
     }
+
+    /// Returns a reference to underlying public key
+    pub fn as_inner(&self) -> &PublicKey {
+        &self.0
+    }
+
 }