Merge rust-bitcoin/rust-bitcoin#4189: Private key from slice fix

ecc5791930 Add test checking `XOnlyPublicKey::deserialize` (Martin Habovstiak)
bbe87eccf2 Fix bug in PSBT `Deserialize` for `XOnlyPublicKey` (Martin Habovstiak)
8efacd4dda Deprecate `PrivateKey::from_slice` method (Martin Habovstiak)
0d5cd7af43 Add `from_byte_array` to `PrivateKey`. (Martin Habovstiak)
1778fea66e Add a test checking `PrivateKey::from_slice` (Martin Habovstiak)
b87ddc0043 Don't panic in `PrivateKey::from_slice` (Martin Habovstiak)

Pull request description:

  This fixes the bug introduced in #4154 and deprecates `from_slice` method in favor of `from_byte_array` (see commits).

  Closes #4191

ACKs for top commit:
  jamillambert:
    ACK ecc5791930
  apoelstra:
    ACK ecc5791930b88581fcbc8f2417b0221486bd1031; successfully ran local tests

Tree-SHA512: 05117c68db7b46605dba6104ee7696220416f4efaef1fff01843a910037e4c96bfebc45fcdd16f875e5e800bb33af17193c4aa9b0b1593807df5153e7e935c22

bitcoin/src/crypto/key.rs

@@ -459,17 +459,22 @@ impl PrivateKey {
     /// Serializes the private key to bytes.
     pub fn to_vec(self) -> Vec<u8> { self.inner[..].to_vec() }
 
+    /// Deserializes a private key from a byte array.
+    pub fn from_byte_array(
+        data: [u8; 32],
+        network: impl Into<NetworkKind>
+    ) -> Result<PrivateKey, secp256k1::Error> {
+        Ok(PrivateKey::new(secp256k1::SecretKey::from_byte_array(&data)?, network))
+    }
+
     /// Deserializes a private key from a slice.
+    #[deprecated(since = "TBD", note = "use from_byte_array instead")]
     pub fn from_slice(
         data: &[u8],
         network: impl Into<NetworkKind>,
     ) -> Result<PrivateKey, secp256k1::Error> {
-        Ok(PrivateKey::new(
-            secp256k1::SecretKey::from_byte_array(
-                data[..32].try_into().expect("Slice should be exactly 32 bytes"),
-            )?,
-            network,
-        ))
+        let array = data.try_into().map_err(|_| secp256k1::Error::InvalidSecretKey)?;
+        Self::from_byte_array(array, network)
     }
 
     /// Formats the private key to WIF format.
@@ -1600,4 +1605,13 @@ mod tests {
             panic!("Expected Invalid char error");
         }
     }
+
+    #[test]
+    #[allow(deprecated)] // tests the deprecated function
+    #[allow(deprecated_in_future)]
+    fn invalid_private_key_len() {
+        use crate::Network;
+        assert!(PrivateKey::from_slice(&[1u8; 31], Network::Regtest).is_err());
+        assert!(PrivateKey::from_slice(&[1u8; 33], Network::Regtest).is_err());
+    }
 }

bitcoin/src/psbt/serialize.rs

@@ -261,7 +261,7 @@ impl Serialize for XOnlyPublicKey {
 impl Deserialize for XOnlyPublicKey {
     fn deserialize(bytes: &[u8]) -> Result<Self, Error> {
         XOnlyPublicKey::from_byte_array(
-            bytes[..32].try_into().expect("statistically impossible to hit"),
+            bytes.try_into().map_err(|_| Error::InvalidXOnlyPublicKey)?,
         )
         .map_err(|_| Error::InvalidXOnlyPublicKey)
     }
@@ -461,6 +461,12 @@ mod tests {
         assert!(sighash.is_ok())
     }
 
+    #[test]
+    fn deserialize_xonly_public_key_len() {
+        assert!(XOnlyPublicKey::deserialize(&[1; 31]).is_err());
+        assert!(XOnlyPublicKey::deserialize(&[1; 33]).is_err());
+    }
+
     #[test]
     #[should_panic(expected = "InvalidMagic")]
     fn invalid_vector_1() {