From 7c565ec7a65e423756c42fc89b28a4fa7fccf80e Mon Sep 17 00:00:00 2001
From: Dr Maxim Orlovsky <orlovsky@pandoracore.com>
Date: Sun, 1 Aug 2021 21:03:58 +0200
Subject: [PATCH] BIP32 extended key `to_ecdsa()` and `to_schnorr()` methods

---
 examples/bip32.rs    |  2 +-
 src/util/bip32.rs    | 41 +++++++++++++++++++++++++++++++++++------
 src/util/psbt/mod.rs |  2 +-
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/examples/bip32.rs b/examples/bip32.rs
index e6a232f065..0a005bb1d5 100644
--- a/examples/bip32.rs
+++ b/examples/bip32.rs
@@ -49,7 +49,7 @@ fn main() {
     let path = DerivationPath::from_str("m/84h/0h/0h").unwrap();
     let child = root.derive_priv(&secp, &path).unwrap();
     println!("Child at {}: {}", path, child);
-    let xpub = ExtendedPubKey::from_private(&secp, &child);
+    let xpub = ExtendedPubKey::from_priv(&secp, &child);
     println!("Public key at {}: {}", path, xpub);
 
     // generate first receiving address at m/0/0
diff --git a/src/util/bip32.rs b/src/util/bip32.rs
index 640e65d085..a0dc2ac3de 100644
--- a/src/util/bip32.rs
+++ b/src/util/bip32.rs
@@ -28,7 +28,7 @@ use secp256k1::{self, Secp256k1};
 
 use network::constants::Network;
 use util::{base58, endian};
-use util::key;
+use util::{key, ecdsa, schnorr};
 use io::Write;
 
 /// A chain code
@@ -507,6 +507,21 @@ impl ExtendedPrivKey {
         })
     }
 
+    /// Constructs ECDSA compressed private key matching internal secret key representation.
+    pub fn to_ecdsa_priv(&self) -> ecdsa::PrivateKey {
+        ecdsa::PrivateKey {
+            compressed: true,
+            network: self.network,
+            key: self.private_key
+        }
+    }
+
+    /// Constructs BIP340 keypair for Schnorr signatures and Taproot use matching the internal
+    /// secret key representation.
+    pub fn to_schnorr_keypair<C: secp256k1::Signing>(&self, secp: &Secp256k1<C>) -> schnorr::KeyPair {
+        schnorr::KeyPair::from_seckey_slice(secp, &self.private_key[..]).expect("BIP32 internal private key representation is broken")
+    }
+
     /// Attempts to derive an extended private key from a path.
     ///
     /// The `path` argument can be both of type `DerivationPath` or `Vec<ChildNumber>`.
@@ -596,7 +611,7 @@ impl ExtendedPrivKey {
 
     /// Returns the HASH160 of the public key belonging to the xpriv
     pub fn identifier<C: secp256k1::Signing>(&self, secp: &Secp256k1<C>) -> XpubIdentifier {
-        ExtendedPubKey::from_private(secp, self).identifier()
+        ExtendedPubKey::from_priv(secp, self).identifier()
     }
 
     /// Returns the first four bytes of the identifier
@@ -607,7 +622,7 @@ impl ExtendedPrivKey {
 
 impl ExtendedPubKey {
     /// Derives a public key from a private key
-    pub fn from_private<C: secp256k1::Signing>(secp: &Secp256k1<C>, sk: &ExtendedPrivKey) -> ExtendedPubKey {
+    pub fn from_priv<C: secp256k1::Signing>(secp: &Secp256k1<C>, sk: &ExtendedPrivKey) -> ExtendedPubKey {
         ExtendedPubKey {
             network: sk.network,
             depth: sk.depth,
@@ -618,6 +633,20 @@ impl ExtendedPubKey {
         }
     }
 
+    /// Constructs ECDSA compressed public key matching internal public key representation.
+    pub fn to_ecdsa_pub(&self) -> ecdsa::PublicKey {
+        ecdsa::PublicKey {
+            compressed: true,
+            key: self.public_key
+        }
+    }
+
+    /// Constructs BIP340 x-only public key for BIP-340 signatures and Taproot use matching
+    /// the internal public key representation.
+    pub fn to_schnorr_pub(&self) -> schnorr::PublicKey {
+        schnorr::PublicKey::from(self.public_key)
+    }
+
     /// Attempts to derive an extended public key from a path.
     ///
     /// The `path` argument can be both of type `DerivationPath` or `Vec<ChildNumber>`.
@@ -849,7 +878,7 @@ mod tests {
                  expected_pk: &str) {
 
         let mut sk = ExtendedPrivKey::new_master(network, seed).unwrap();
-        let mut pk = ExtendedPubKey::from_private(secp, &sk);
+        let mut pk = ExtendedPubKey::from_priv(secp, &sk);
 
         // Check derivation convenience method for ExtendedPrivKey
         assert_eq!(
@@ -877,7 +906,7 @@ mod tests {
             match num {
                 Normal {..} => {
                     let pk2 = pk.ckd_pub(secp, num).unwrap();
-                    pk = ExtendedPubKey::from_private(secp, &sk);
+                    pk = ExtendedPubKey::from_priv(secp, &sk);
                     assert_eq!(pk, pk2);
                 }
                 Hardened {..} => {
@@ -885,7 +914,7 @@ mod tests {
                         pk.ckd_pub(secp, num),
                         Err(Error::CannotDeriveFromHardenedKey)
                     );
-                    pk = ExtendedPubKey::from_private(secp, &sk);
+                    pk = ExtendedPubKey::from_priv(secp, &sk);
                 }
             }
         }
diff --git a/src/util/psbt/mod.rs b/src/util/psbt/mod.rs
index 3a9df2e2aa..012025dfe2 100644
--- a/src/util/psbt/mod.rs
+++ b/src/util/psbt/mod.rs
@@ -281,7 +281,7 @@ mod tests {
 
         sk = sk.derive_priv(secp, &dpath).unwrap();
 
-        let pk: ExtendedPubKey = ExtendedPubKey::from_private(&secp, &sk);
+        let pk: ExtendedPubKey = ExtendedPubKey::from_priv(&secp, &sk);
 
         hd_keypaths.insert(pk.public_key, (fprint, dpath.into()));