Fix signature key import/export, add tests

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

vault/src/error.rs

@@ -44,6 +44,8 @@ pub enum CryptoError {
     SignatureFailed,
     /// The signature does not have the expected size
     InvalidSignatureSize,
+    /// Trying to load a key which is not the expected format,
+    InvalidKey,
 }
 
 impl core::fmt::Display for CryptoError {
@@ -57,6 +59,7 @@ impl core::fmt::Display for CryptoError {
             CryptoError::InvalidSignatureSize => {
                 f.write_str("provided signature does not have the expected size")
             }
+            CryptoError::InvalidKey => f.write_str("the provided bytes are not a valid key"),
         }
     }
 }
@@ -92,3 +95,9 @@ impl From<bincode::error::EncodeError> for Error {
         Self::Coding
     }
 }
+
+impl From<k256::ecdsa::Error> for CryptoError {
+    fn from(_: k256::ecdsa::Error) -> Self {
+        Self::InvalidKey
+    }
+}

vault/src/key/signature.rs

@@ -12,6 +12,7 @@ pub struct SigningKeypair {
     vk: VerifyingKey,
 }
 
+#[derive(Debug, PartialEq, Eq)]
 pub struct PublicKey(VerifyingKey);
 
 impl SigningKeypair {
@@ -58,13 +59,14 @@ impl SigningKeypair {
 impl PublicKey {
     /// Import a public key from raw bytes
     pub fn from_bytes(bytes: &[u8]) -> Result<Self, CryptoError> {
-        if bytes.len() == 64 {
-            Ok(Self(
-                VerifyingKey::from_sec1_bytes(bytes).expect("Key is of valid size"),
-            ))
-        } else {
-            Err(CryptoError::InvalidKeySize)
-        }
+        Ok(Self(VerifyingKey::from_sec1_bytes(bytes)?))
+    }
+
+    /// Get the raw bytes of this `PublicKey`, which can be transferred to another party.
+    ///
+    /// The public key is SEC-1 encoded and compressed.
+    pub fn as_bytes(&self) -> Box<[u8]> {
+        self.0.to_encoded_point(true).to_bytes()
     }
 
     pub fn verify_signature(&self, message: &[u8], sig: &[u8]) -> Result<(), CryptoError> {
@@ -74,3 +76,67 @@ impl PublicKey {
             .map_err(|_| CryptoError::SignatureFailed)
     }
 }
+
+#[cfg(test)]
+mod tests {
+
+    /// Generate a key, get the public key, export the bytes of said public key, import them again
+    /// as a public key, and verify the keys match. This make sure public keys can be exchanged.
+    #[test]
+    fn recover_public_key() {
+        let sk = super::SigningKeypair::new().expect("Can generate new key");
+        let pk = sk.public_key();
+        let pk_bytes = pk.as_bytes();
+
+        let pk2 = super::PublicKey::from_bytes(&pk_bytes).expect("Can import public key");
+
+        assert_eq!(pk, pk2);
+    }
+
+    /// Sign a message and validate the signature with the public key. Together with the above test
+    /// this makes sure a remote system can receive our public key and validate messages we sign.
+    #[test]
+    fn validate_signature() {
+        let sk = super::SigningKeypair::new().expect("Can generate new key");
+        let pk = sk.public_key();
+
+        let message = b"this is an arbitrary message we want to sign";
+
+        let sig = sk.sign(message).expect("Message can be signed");
+
+        assert!(pk.verify_signature(message, &sig).is_ok());
+    }
+
+    /// Make sure a signature which is tampered with does not pass signature validation
+    #[test]
+    fn corrupt_signature_does_not_validate() {
+        let sk = super::SigningKeypair::new().expect("Can generate new key");
+        let pk = sk.public_key();
+
+        let message = b"this is an arbitrary message we want to sign";
+
+        let mut sig = sk.sign(message).expect("Message can be signed");
+
+        // Tamper with the sig
+        sig[0] = sig[0].wrapping_add(1);
+
+        assert!(pk.verify_signature(message, &sig).is_err());
+    }
+
+    /// Make sure a valid signature does not work for a message which has been modified
+    #[test]
+    fn tampered_message_does_not_validate() {
+        let sk = super::SigningKeypair::new().expect("Can generate new key");
+        let pk = sk.public_key();
+
+        let message = b"this is an arbitrary message we want to sign";
+        let mut message_clone = message.to_vec();
+
+        let sig = sk.sign(message).expect("Message can be signed");
+
+        // Modify the message
+        message_clone[0] = message[0].wrapping_add(1);
+
+        assert!(pk.verify_signature(&message_clone, &sig).is_err());
+    }
+}