Merge rust-bitcoin/rust-secp256k1#618: Add a verify function to PublicKey

d60b891126 Add a verify function to PublicKey (Tobin C. Harding)

Pull request description:

  Expose signature verification functionality for schnorr signatures on the `XOnlyPublicKey` type.

  Idea from Kixunil: https://github.com/rust-bitcoin/rust-bitcoin/pull/1744#issuecomment-1534200841

ACKs for top commit:
  apoelstra:
    ACK d60b891126

Tree-SHA512: 2ffa3de528b857c5b0a402815b71b35da913c668bea53b63801705fa6a86eb6d44766aa2395c02f67a4712b451c77caf627af9450183ae70957abf246a63c279

src/key.rs

@@ -12,12 +12,10 @@ use serde::ser::SerializeTuple;
 
 use crate::ffi::types::c_uint;
 use crate::ffi::{self, CPtr};
-#[cfg(all(feature = "global-context", feature = "rand-std"))]
-use crate::schnorr;
 use crate::Error::{self, InvalidPublicKey, InvalidPublicKeySum, InvalidSecretKey};
-use crate::{constants, from_hex, Scalar, Secp256k1, Signing, Verification};
+use crate::{constants, from_hex, schnorr, Message, Scalar, Secp256k1, Signing, Verification};
 #[cfg(feature = "global-context")]
-use crate::{ecdsa, Message, SECP256K1};
+use crate::{ecdsa, SECP256K1};
 #[cfg(feature = "bitcoin_hashes")]
 use crate::{hashes, ThirtyTwoByteHash};
 
@@ -1316,6 +1314,16 @@ impl XOnlyPublicKey {
     pub fn public_key(&self, parity: Parity) -> PublicKey {
         PublicKey::from_x_only_public_key(*self, parity)
     }
+
+    /// Checks that `sig` is a valid schnorr signature for `msg` using this public key.
+    pub fn verify<C: Verification>(
+        &self,
+        secp: &Secp256k1<C>,
+        msg: &Message,
+        sig: &schnorr::Signature,
+    ) -> Result<(), Error> {
+        secp.verify_schnorr(sig, msg, self)
+    }
 }
 
 /// Represents the parity passed between FFI function calls.