Merge rust-bitcoin/rust-bitcoin#696: Taproot tweaks generalization & KeyPair support

7405836411 Fix warning about deprecated method use (Dr Maxim Orlovsky)
f39b1300fa CI: do not fail fast (Dr Maxim Orlovsky)
f77c57195a Making Script method new_* names more consistent (Dr Maxim Orlovsky)
91b68a468d Taproot-related methods for Script type (Dr Maxim Orlovsky)
599c5f9488 Generalizing taproot key tweaking for KeyPairs (Dr Maxim Orlovsky)

Pull request description:

  * Adds taproot-related methods to `Script`
  * Fixes API for existing taproot methods
  * Generalizes `TapTweak` trait to work with both public keys and key pairs

  ~~UPD: PR is pending https://github.com/rust-bitcoin/rust-secp256k1/pull/342~~

ACKs for top commit:
  sanket1729:
    ACK 7405836411
  apoelstra:
    ACK 7405836411

Tree-SHA512: 4a76dfffa1452baadc15e19812831ef9d2e66794c090a8fc123388d7119b2c8a1f0420ce723ad22e01683c8198711fe62e0cdf00c9ad2d2974606383baaf1cb0

.github/workflows/rust.yml

@@ -7,6 +7,7 @@ jobs:
     name: Tests
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
         include:
           - rust: stable

src/blockdata/script.rs

@@ -41,6 +41,9 @@ use policy::DUST_RELAY_TX_FEE;
 
 use util::ecdsa::PublicKey;
 use util::address::WitnessVersion;
+use util::taproot::{LeafVersion, TapBranchHash, TapLeafHash};
+use secp256k1::{Secp256k1, Verification};
+use schnorr::{TapTweak, TweakedPublicKey, UntweakedPublicKey};
 
 /// A Bitcoin script.
 #[derive(Clone, Default, PartialOrd, Ord, PartialEq, Eq, Hash)]
@@ -312,13 +315,40 @@ impl Script {
     }
 
     /// Generates P2WPKH-type of scriptPubkey
+    #[deprecated(since = "0.28.0", note = "use Script::new_v0_p2wpkh method instead")]
     pub fn new_v0_wpkh(pubkey_hash: &WPubkeyHash) -> Script {
-        Script::new_witness_program(WitnessVersion::V0, &pubkey_hash.to_vec())
+        Script::new_v0_p2wpkh(pubkey_hash)
+    }
+
+    /// Generates P2WPKH-type of scriptPubkey
+    pub fn new_v0_p2wpkh(pubkey_hash: &WPubkeyHash) -> Script {
+        Script::new_witness_program(WitnessVersion::V0, &pubkey_hash[..])
     }
 
     /// Generates P2WSH-type of scriptPubkey with a given hash of the redeem script
+    #[deprecated(since = "0.28.0", note = "use Script::new_v0_p2wsh method instead")]
     pub fn new_v0_wsh(script_hash: &WScriptHash) -> Script {
-        Script::new_witness_program(WitnessVersion::V0, &script_hash.to_vec())
+        Script::new_v0_p2wsh(script_hash)
+    }
+
+    /// Generates P2WSH-type of scriptPubkey with a given hash of the redeem script
+    pub fn new_v0_p2wsh(script_hash: &WScriptHash) -> Script {
+        Script::new_witness_program(WitnessVersion::V0, &script_hash[..])
+    }
+
+    /// Generates P2TR for script spending path using an internal public key and some optional
+    /// script tree merkle root.
+    pub fn new_v1_p2tr<C: Verification>(secp: &Secp256k1<C>, internal_key: UntweakedPublicKey, merkle_root: Option<TapBranchHash>) -> Script {
+        let (output_key, _) = internal_key.tap_tweak(secp, merkle_root);
+        Script::new_witness_program(WitnessVersion::V1, &output_key.serialize())
+    }
+
+    /// Generates P2TR for key spending path for a known [`TweakedPublicKey`].
+    ///
+    /// NB: Make sure that the used key is indeed tweaked (for instance, it comes from `rawtr`
+    /// descriptor content); otherwise please use [`Script::new_v1_p2tr`] method.
+    pub fn new_v1_p2tr_tweaked(output_key: TweakedPublicKey) -> Script {
+        Script::new_witness_program(WitnessVersion::V1, &output_key.serialize())
     }
 
     /// Generates P2WSH-type of scriptPubkey with a given hash of the redeem script
@@ -370,7 +400,21 @@ impl Script {
     /// Compute the P2WSH output corresponding to this witnessScript (aka the "witness redeem
     /// script")
     pub fn to_v0_p2wsh(&self) -> Script {
-        Script::new_v0_wsh(&self.wscript_hash())
+        Script::new_v0_p2wsh(&self.wscript_hash())
+    }
+
+    /// Compute P2TR output with a given internal key and a single script spending path equal to the
+    /// current script, assuming that the script is a Tapscript
+    #[inline]
+    pub fn to_v1_p2tr<C: Verification>(&self, secp: &Secp256k1<C>, internal_key: UntweakedPublicKey) -> Script {
+        let leaf_hash = TapLeafHash::from_script(&self, LeafVersion::TapScript);
+        let merkle_root = TapBranchHash::from_inner(leaf_hash.into_inner());
+        Script::new_v1_p2tr(&secp, internal_key, Some(merkle_root))
+    }
+
+    #[inline]
+    fn witness_version(&self) -> Option<WitnessVersion> {
+        WitnessVersion::from_opcode(self.0[0].into()).ok()
     }
 
     /// Checks whether a script pubkey is a p2sh output
@@ -428,18 +472,26 @@ impl Script {
     #[inline]
     pub fn is_v0_p2wsh(&self) -> bool {
         self.0.len() == 34 &&
-        self.0[0] == opcodes::all::OP_PUSHBYTES_0.into_u8() &&
+            self.witness_version() == Some(WitnessVersion::V0) &&
-        self.0[1] == opcodes::all::OP_PUSHBYTES_32.into_u8()
+            self.0[1] == opcodes::all::OP_PUSHBYTES_32.into_u8()
     }
 
     /// Checks whether a script pubkey is a p2wpkh output
     #[inline]
     pub fn is_v0_p2wpkh(&self) -> bool {
         self.0.len() == 22 &&
-            self.0[0] == opcodes::all::OP_PUSHBYTES_0.into_u8() &&
+            self.witness_version() == Some(WitnessVersion::V0) &&
             self.0[1] == opcodes::all::OP_PUSHBYTES_20.into_u8()
     }
 
+    /// Checks whether a script pubkey is a P2TR output
+    #[inline]
+    pub fn is_v1_p2tr(&self) -> bool {
+        self.0.len() == 34 &&
+            self.witness_version() == Some(WitnessVersion::V1) &&
+            self.0[1] == opcodes::all::OP_PUSHBYTES_32.into_u8()
+    }
+
     /// Check if this is an OP_RETURN output
     pub fn is_op_return (&self) -> bool {
         !self.0.is_empty() && (opcodes::All::from(self.0[0]) == opcodes::all::OP_RETURN)
@@ -1042,7 +1094,7 @@ mod test {
         assert!(Script::new_p2pkh(&pubkey_hash).is_p2pkh());
 
         let wpubkey_hash = WPubkeyHash::hash(&pubkey.inner.serialize());
-        assert!(Script::new_v0_wpkh(&wpubkey_hash).is_v0_p2wpkh());
+        assert!(Script::new_v0_p2wpkh(&wpubkey_hash).is_v0_p2wpkh());
 
         let script = Builder::new().push_opcode(opcodes::all::OP_NUMEQUAL)
                                    .push_verify()
@@ -1053,7 +1105,7 @@ mod test {
         assert_eq!(script.to_p2sh(), p2sh);
 
         let wscript_hash = WScriptHash::hash(&script.serialize());
-        let p2wsh = Script::new_v0_wsh(&wscript_hash);
+        let p2wsh = Script::new_v0_p2wsh(&wscript_hash);
         assert!(p2wsh.is_v0_p2wsh());
         assert_eq!(script.to_v0_p2wsh(), p2wsh);
 

src/util/misc.rs

@@ -320,7 +320,7 @@ mod tests {
         let msg = secp256k1::Message::from_slice(&msg_hash).unwrap();
 
         let privkey = secp256k1::SecretKey::new(&mut secp256k1::rand::thread_rng());
-        let secp_sig = secp.sign_recoverable(&msg, &privkey);
+        let secp_sig = secp.sign_ecdsa_recoverable(&msg, &privkey);
         let signature = super::MessageSignature {
             signature: secp_sig,
             compressed: true,

src/util/schnorr.rs

@@ -26,10 +26,10 @@ use hashes::Hash;
 use util::taproot::{TapBranchHash, TapTweakHash};
 use SchnorrSigHashType;
 
-/// Untweaked Schnorr public key
+/// Untweaked BIP-340 X-coord-only public key
 pub type UntweakedPublicKey = XOnlyPublicKey;
 
-/// Tweaked Schnorr public key
+/// Tweaked BIP-340 X-coord-only public key
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct TweakedPublicKey(XOnlyPublicKey);
 
@@ -45,29 +45,59 @@ impl fmt::Display for TweakedPublicKey {
     }
 }
 
-/// A trait for tweaking Schnorr public keys
+/// Untweaked BIP-340 key pair
+pub type UntweakedKeyPair = KeyPair;
+
+/// Tweaked BIP-340 key pair
+#[derive(Clone)]
+#[cfg_attr(feature = "std", derive(Debug))]
+// TODO: Add other derives once secp256k1 v0.21.3 released
+pub struct TweakedKeyPair(KeyPair);
+
+/// A trait for tweaking BIP340 key types (x-only public keys and key pairs).
 pub trait TapTweak {
-    /// Tweaks an untweaked public key given an untweaked key and optional script tree merkle root.
+    /// Tweaked key type with optional auxiliary information
+    type TweakedAux;
+    /// Tweaked key type
+    type TweakedKey;
+
+    /// Tweaks an untweaked key with corresponding public key value and optional script tree merkle
+    /// root. For the [`KeyPair`] type this also tweaks the private key in the pair.
     ///
     /// This is done by using the equation Q = P + H(P|c)G, where
-    ///  * Q is the tweaked key
+    ///  * Q is the tweaked public key
-    ///  * P is the internal key
+    ///  * P is the internal public key
     ///  * H is the hash function
     ///  * c is the commitment data
     ///  * G is the generator point
     ///
     /// # Returns
     /// The tweaked key and its parity.
-    fn tap_tweak<C: Verification>(self, secp: &Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> (TweakedPublicKey, secp256k1::Parity);
+    fn tap_tweak<C: Verification>(self, secp: &Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> Self::TweakedAux;
 
     /// Directly converts 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;
+    fn dangerous_assume_tweaked(self) -> Self::TweakedKey;
 }
 
 impl TapTweak for UntweakedPublicKey {
+    type TweakedAux = (TweakedPublicKey, secp256k1::Parity);
+    type TweakedKey = TweakedPublicKey;
+
+    /// Tweaks an untweaked public key with corresponding public key value and optional script tree
+    /// merkle root.
+    ///
+    /// This is done by using the equation Q = P + H(P|c)G, where
+    ///  * Q is the tweaked public key
+    ///  * P is the internal public key
+    ///  * H is the hash function
+    ///  * c is the commitment data
+    ///  * G is the generator point
+    ///
+    /// # Returns
+    /// The tweaked key and its parity.
     fn tap_tweak<C: Verification>(self, secp: &Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> (TweakedPublicKey, secp256k1::Parity) {
         let tweak_value = TapTweakHash::from_key_and_tweak(self, merkle_root).into_inner();
         let mut output_key = self.clone();
@@ -82,9 +112,42 @@ impl TapTweak for UntweakedPublicKey {
     }
 }
 
+impl TapTweak for UntweakedKeyPair {
+    type TweakedAux = TweakedKeyPair;
+    type TweakedKey = TweakedKeyPair;
+
+    /// Tweaks private and public keys within an untweaked [`KeyPair`] with corresponding public key
+    /// value and optional script tree merkle root.
+    ///
+    /// This is done by tweaking private key within the pair using the equation q = p + H(P|c), where
+    ///  * q is the tweaked private key
+    ///  * p is the internal private key
+    ///  * H is the hash function
+    ///  * c is the commitment data
+    /// The public key is generated from a private key by multiplying with generator point, Q = qG.
+    ///
+    /// # Returns
+    /// The tweaked key and its parity.
+    fn tap_tweak<C: Verification>(self, secp: &Secp256k1<C>, merkle_root: Option<TapBranchHash>) -> TweakedKeyPair {
+        let pubkey = XOnlyPublicKey::from_keypair(&self);
+        let tweak_value = TapTweakHash::from_key_and_tweak(pubkey, merkle_root).into_inner();
+        let mut output_key = self.clone();
+        output_key.tweak_add_assign(&secp, &tweak_value).expect("Tap tweak failed");
+        TweakedKeyPair(output_key)
+    }
+
+    fn dangerous_assume_tweaked(self) -> TweakedKeyPair {
+        TweakedKeyPair(self)
+    }
+}
+
 impl TweakedPublicKey {
     /// Creates a new [`TweakedPublicKey`] from a [`XOnlyPublicKey`]. No tweak is applied, consider
     /// calling `tap_tweak` on an [`UntweakedPublicKey`] instead of using this constructor.
+    ///
+    /// 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.
+    #[inline]
     pub fn dangerous_assume_tweaked(key: XOnlyPublicKey) -> TweakedPublicKey {
         TweakedPublicKey(key)
     }
@@ -108,6 +171,24 @@ impl TweakedPublicKey {
     }
 }
 
+impl TweakedKeyPair {
+    /// Creates a new [`TweakedKeyPair`] from a [`KeyPair`]. No tweak is applied, consider
+    /// calling `tap_tweak` on an [`UntweakedKeyPair`] instead of using this constructor.
+    ///
+    /// 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.
+    #[inline]
+    pub fn dangerous_assume_tweaked(pair: KeyPair) -> TweakedKeyPair {
+        TweakedKeyPair(pair)
+    }
+
+    /// Returns the underlying key pair
+    #[inline]
+    pub fn into_inner(self) -> KeyPair {
+        self.0
+    }
+}
+
 /// A BIP340-341 serialized schnorr signature with the corresponding hash type.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -119,7 +200,6 @@ pub struct SchnorrSig {
 }
 
 impl SchnorrSig {
-
     /// Deserialize from slice
     pub fn from_slice(sl: &[u8]) -> Result<Self, SchnorrSigError> {
         match sl.len() {