Adding KeyPair::serialize_sec. Closes #298

Cargo.toml

@@ -7,7 +7,7 @@ license = "CC0-1.0"
 homepage = "https://github.com/rust-bitcoin/rust-secp256k1/"
 repository = "https://github.com/rust-bitcoin/rust-secp256k1/"
 documentation = "https://docs.rs/secp256k1/"
-description = "Rust bindings for Pieter Wuille's `libsecp256k1` library. Implements ECDSA for the SECG elliptic curve group secp256k1 and related utilities."
+description = "Rust wrapper library for Pieter Wuille's `libsecp256k1`. Implements ECDSA and BIP 340 signatures for the SECG elliptic curve group secp256k1 and related utilities."
 keywords = [ "crypto", "ECDSA", "secp256k1", "libsecp256k1", "bitcoin" ]
 readme = "README.md"
 autoexamples = false # Remove when edition 2018 https://github.com/rust-lang/cargo/issues/5330

src/schnorrsig.rs

@@ -211,6 +211,12 @@ impl KeyPair {
         }
     }
 
+    /// Serialize the key pair as a secret key byte value
+    #[inline]
+    pub fn serialize_sec<V: Verification>(&self, secp: &Secp256k1<V>) -> [u8; constants::SECRET_KEY_SIZE] {
+        *SecretKey::from_keypair(secp, self).as_ref()
+    }
+
     /// Tweak a keypair by adding the given tweak to the secret key and updating the
     /// public key accordingly.
     /// Will return an error if the resulting key would be invalid or if