public static byte[] EncryptWithChecksum(PrivateKey privateKey, PublicKey publicKey, UInt64 nonce, string message)
{
byte[] shareSecret = privateKey.SharedSecret(publicKey);
byte[] sharedSecretUTF8Bytes = Encoding.UTF8.GetBytes(Hex.BytesToHex(shareSecret));
byte[] nonceBytes = Encoding.UTF8.GetBytes("" + nonce);
byte[] seed = nonceBytes.Concat(sharedSecretUTF8Bytes).ToArray();
string hash = Hex.BytesToHex(Hash.SHA512(seed));
byte[] key = Hex.HexToBytes(hash.Substring(0, 64));
byte[] iv = Hex.HexToBytes(hash.Substring(64, 32));
byte[] encodedMsg = Encoding.UTF8.GetBytes(message);
byte[] checksum = Hash.SHA256(encodedMsg).Take(4).ToArray();
return(EncryptStringToBytes(checksum.Concat(encodedMsg).ToArray(), key, iv));
}
public static string DecryptWithChecksum(PrivateKey privateKey, PublicKey publicKey, UInt64 nonce, byte[] payload)
{
byte[] shareSecret = privateKey.SharedSecret(publicKey);
byte[] sharedSecretUTF8Bytes = Encoding.UTF8.GetBytes(Hex.BytesToHex(shareSecret));
byte[] nonceBytes = Encoding.UTF8.GetBytes("" + nonce);
byte[] seed = nonceBytes.Concat(sharedSecretUTF8Bytes).ToArray();
string hash = Hex.BytesToHex(Hash.SHA512(seed));
byte[] key = Hex.HexToBytes(hash.Substring(0, 64));
byte[] iv = Hex.HexToBytes(hash.Substring(64, 32));
byte[] decryptedMsg = DecryptStringFromBytes(payload, key, iv);
byte[] checksum = decryptedMsg.Take(4).ToArray();
byte[] message = decryptedMsg.Skip(4).ToArray();
byte[] newChecksum = Hash.SHA256(message).Take(4).ToArray();
if (!checksum.SequenceEqual(newChecksum))
{
throw new Exception($"Invalid checksum, expected {Hex.BytesToHex(newChecksum)}, got {Hex.BytesToHex(checksum)}");
}
return(Encoding.UTF8.GetString(message));
}
