Add tests for asymmetric keys, add public key export

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

vault/src/error.rs

@@ -101,3 +101,9 @@ impl From<k256::ecdsa::Error> for CryptoError {
         Self::InvalidKey
     }
 }
+
+impl From<k256::elliptic_curve::Error> for CryptoError {
+    fn from(_: k256::elliptic_curve::Error) -> Self {
+        Self::InvalidKey
+    }
+}

vault/src/key/asymmetric.rs

@@ -1,10 +1,7 @@
 //! An implementation of asymmetric cryptography using SECP256k1 ECDH with ChaCha20Poly1305
 //! for the actual encryption.
 
-use k256::{
-    SecretKey,
-    ecdh::diffie_hellman,
-};
+use k256::{SecretKey, ecdh::diffie_hellman, elliptic_curve::sec1::ToEncodedPoint};
 use sha2::Sha256;
 
 use crate::{error::CryptoError, key::symmetric::SymmetricKey};
@@ -18,6 +15,7 @@ pub struct AsymmetricKeypair {
 }
 
 /// The public key part of an asymmetric keypair.
+#[derive(Debug, PartialEq, Eq)]
 pub struct PublicKey(k256::PublicKey);
 
 impl AsymmetricKeypair {
@@ -101,12 +99,63 @@ impl AsymmetricKeypair {
 impl PublicKey {
     /// Import a public key from raw bytes
     pub fn from_bytes(bytes: &[u8]) -> Result<Self, CryptoError> {
-        if bytes.len() == 64 {
-            Ok(Self(
-                k256::PublicKey::from_sec1_bytes(bytes).expect("Key is of valid size"),
-            ))
-        } else {
-            Err(CryptoError::InvalidKeySize)
-        }
+        Ok(Self(k256::PublicKey::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()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    /// Export a public key and import it later
+    #[test]
+    fn import_public_key() {
+        let kp = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+        let pk1 = kp.public_key();
+        let pk_bytes = pk1.as_bytes();
+        let pk2 = super::PublicKey::from_bytes(&pk_bytes).expect("Can import public key");
+
+        assert_eq!(pk1, pk2);
+    }
+    /// Make sure 2 random keypairs derive the same shared secret (and thus encryption key), by
+    /// encrypting a random message, decrypting it, and verifying it matches.
+    #[test]
+    fn encrypt_and_decrypt() {
+        let kp1 = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+        let kp2 = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+
+        let pk1 = kp1.public_key();
+        let pk2 = kp2.public_key();
+
+        let message = b"this is a random message to encrypt and decrypt";
+
+        let enc = kp1.encrypt(&pk2, message).expect("Can encrypt message");
+        let dec = kp2.decrypt(&pk1, &enc).expect("Can decrypt message");
+
+        assert_eq!(message.as_slice(), dec.as_slice());
+    }
+
+    /// Use a different public key for decrypting than the expected one, this should fail the
+    /// decryption process as we use AEAD encryption with the symmetric key.
+    #[test]
+    fn decrypt_with_wrong_key() {
+        let kp1 = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+        let kp2 = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+        let kp3 = super::AsymmetricKeypair::new().expect("Can generate new keypair");
+
+        let pk2 = kp2.public_key();
+        let pk3 = kp3.public_key();
+
+        let message = b"this is a random message to encrypt and decrypt";
+
+        let enc = kp1.encrypt(&pk2, message).expect("Can encrypt message");
+        let dec = kp2.decrypt(&pk3, &enc);
+
+        assert!(dec.is_err());
     }
 }

vault/src/key/symmetric.rs

@@ -69,8 +69,8 @@ impl SymmetricKey {
 
         // Extract nonce from the end of ciphertext
         let ciphertext_len = ciphertext.len() - NONCE_SIZE;
-        let ciphertext = &ciphertext[0..ciphertext_len];
         let nonce_bytes = &ciphertext[ciphertext_len..];
+        let ciphertext = &ciphertext[0..ciphertext_len];
 
         // Create cipher
         let cipher = ChaCha20Poly1305::new_from_slice(&self.0)