feat: KeyPair::from_seckey_byte_array

Construct KeyPair directly from [u8; 32].
Deprecate KeyPair::from_seckey_slice
and replace all of its calls with the new method.

src/key.rs

@@ -859,16 +859,29 @@ impl Keypair {
     /// # Errors
     ///
     /// [`Error::InvalidSecretKey`] if the slice is not exactly 32 bytes long,
-    /// or if the encoded number exceeds the Secp256k1 field `p` value.
+    /// or if the encoded number is an invalid scalar.
+    #[deprecated(since = "TBD", note = "Use `from_seckey_byte_array` instead.")]
     #[inline]
     pub fn from_seckey_slice<C: Signing>(
         secp: &Secp256k1<C>,
-        data: &[u8],
+        data: [u8; constants::SECRET_KEY_SIZE],
     ) -> Result<Keypair, Error> {
-        if data.is_empty() || data.len() != constants::SECRET_KEY_SIZE {
-            return Err(Error::InvalidSecretKey);
+        match <[u8; constants::SECRET_KEY_SIZE]>::try_from(data) {
+            Ok(data) => Self::from_seckey_byte_array(secp, data),
+            Err(_) => Err(Error::InvalidSecretKey),
         }
+    }
 
+    /// Creates a [`Keypair`] directly from a secret key byte array.
+    ///
+    /// # Errors
+    ///
+    /// [`Error::InvalidSecretKey`] if the encoded number is an invalid scalar.
+    #[inline]
+    pub fn from_seckey_byte_array<C: Signing>(
+        secp: &Secp256k1<C>,
+        data: [u8; constants::SECRET_KEY_SIZE],
+    ) -> Result<Keypair, Error> {
         unsafe {
             let mut kp = ffi::Keypair::new();
             if ffi::secp256k1_keypair_create(secp.ctx.as_ptr(), &mut kp, data.as_c_ptr()) == 1 {
@@ -884,13 +897,12 @@ impl Keypair {
     /// # Errors
     ///
     /// [`Error::InvalidSecretKey`] if the string does not consist of exactly 64 hex characters,
-    /// or if the encoded number exceeds the Secp256k1 field `p` value.
+    /// or if the encoded number is an invalid scalar.
     #[inline]
     pub fn from_seckey_str<C: Signing>(secp: &Secp256k1<C>, s: &str) -> Result<Keypair, Error> {
         let mut res = [0u8; constants::SECRET_KEY_SIZE];
         match from_hex(s, &mut res) {
-            Ok(constants::SECRET_KEY_SIZE) =>
-                Keypair::from_seckey_slice(secp, &res[0..constants::SECRET_KEY_SIZE]),
+            Ok(constants::SECRET_KEY_SIZE) => Keypair::from_seckey_byte_array(secp, res),
             _ => Err(Error::InvalidSecretKey),
         }
     }
@@ -900,7 +912,7 @@ impl Keypair {
     /// # Errors
     ///
     /// [`Error::InvalidSecretKey`] if the string does not consist of exactly 64 hex characters,
-    /// or if the encoded number exceeds the Secp256k1 field `p` value.
+    /// or if the encoded number is an invalid scalar.
     #[inline]
     #[cfg(feature = "global-context")]
     pub fn from_seckey_str_global(s: &str) -> Result<Keypair, Error> {
@@ -1117,7 +1129,7 @@ impl<'de> serde::Deserialize<'de> for Keypair {
                 let ctx = Secp256k1::signing_only();
 
                 #[allow(clippy::needless_borrow)]
-                Keypair::from_seckey_slice(&ctx, &data)
+                Keypair::from_seckey_byte_array(&ctx, data)
             });
             d.deserialize_tuple(constants::SECRET_KEY_SIZE, visitor)
         }
@@ -1665,7 +1677,7 @@ mod test {
     #[cfg(all(feature = "std", not(secp256k1_fuzz)))]
     fn erased_keypair_is_valid() {
         let s = Secp256k1::new();
-        let kp = Keypair::from_seckey_slice(&s, &[1u8; constants::SECRET_KEY_SIZE])
+        let kp = Keypair::from_seckey_byte_array(&s, [1u8; constants::SECRET_KEY_SIZE])
             .expect("valid secret key");
         let mut kp2 = kp;
         kp2.non_secure_erase();
@@ -2272,7 +2284,7 @@ mod test {
         ];
         static SK_STR: &str = "01010101010101010001020304050607ffff0000ffff00006363636363636363";
 
-        let sk = Keypair::from_seckey_slice(SECP256K1, &SK_BYTES).unwrap();
+        let sk = Keypair::from_seckey_byte_array(SECP256K1, SK_BYTES).unwrap();
         #[rustfmt::skip]
         assert_tokens(&sk.compact(), &[
             Token::Tuple{ len: 32 },
@@ -2452,7 +2464,7 @@ mod test {
 
         static PK_STR: &str = "18845781f631c48f1c9709e23092067d06837f30aa0cd0544ac887fe91ddd166";
 
-        let kp = Keypair::from_seckey_slice(crate::SECP256K1, &SK_BYTES).unwrap();
+        let kp = Keypair::from_seckey_byte_array(crate::SECP256K1, SK_BYTES).unwrap();
         let (pk, _parity) = XOnlyPublicKey::from_keypair(&kp);
 
         #[rustfmt::skip]

src/schnorr.rs

@@ -393,7 +393,7 @@ mod tests {
                 0x63, 0x63, 0x63, 0x63,
             ];
 
-            let kp = Keypair::from_seckey_slice(&secp, &SK_BYTES).expect("sk");
+            let kp = Keypair::from_seckey_byte_array(&secp, SK_BYTES).expect("sk");
 
             // In fuzzing mode secret->public key derivation is different, so
             // hard-code the expected result.
@@ -473,7 +473,7 @@ mod tests {
         let s = Secp256k1::new();
 
         let msg = [1; 32];
-        let keypair = Keypair::from_seckey_slice(&s, &[2; 32]).unwrap();
+        let keypair = Keypair::from_seckey_byte_array(&s, [2; 32]).unwrap();
         let aux = [3u8; 32];
         let sig = s.sign_schnorr_with_aux_rand(&msg, &keypair, &aux);
         static SIG_BYTES: [u8; constants::SCHNORR_SIGNATURE_SIZE] = [
@@ -706,7 +706,7 @@ mod tests {
         } in vectors
         {
             if let (Some(secret_key), Some(aux_rand)) = (secret_key, aux_rand) {
-                let keypair = Keypair::from_seckey_slice(&secp, &secret_key).unwrap();
+                let keypair = Keypair::from_seckey_byte_array(&secp, secret_key).unwrap();
                 assert_eq!(keypair.x_only_public_key().0.serialize(), public_key);
                 let sig = secp.sign_schnorr_with_aux_rand(&message, &keypair, &aux_rand);
                 assert_eq!(sig.to_byte_array(), signature);

tests/serde.rs

@@ -61,7 +61,7 @@ fn bincode_public_key() {
 #[cfg(feature = "global-context")]
 fn bincode_keypair() {
     let secp = Secp256k1::new();
-    let kp = Keypair::from_seckey_slice(&secp, &SK_BYTES).expect("failed to create keypair");
+    let kp = Keypair::from_seckey_byte_array(&secp, SK_BYTES).expect("failed to create keypair");
     let ser = bincode::serialize(&kp).unwrap();
 
     assert_eq!(ser, SK_BYTES);