public static byte[] DecryptAndAuthenticate(byte[] key, byte[] nonce, byte[] encryptedData, byte[] associatedData, byte[] signature)
{
if (nonce.Length < 7 || nonce.Length > 13)
{
throw new ArgumentException("nonce length must be between 7 and 13 bytes");
}
if (signature.Length < 4 || signature.Length > 16 || (signature.Length % 2 == 1))
{
throw new ArgumentException("signature length must be an even number between 4 and 16 bytes");
}
byte[] keyStream = BuildKeyStream(key, nonce, encryptedData.Length);
byte[] data = ByteUtils.XOR(encryptedData, 0, keyStream, 16, encryptedData.Length);
byte[] mac = CalculateMac(key, nonce, data, associatedData, signature.Length);
byte[] expectedSignature = ByteUtils.XOR(keyStream, 0, mac, 0, mac.Length);
if (!ByteUtils.AreByteArraysEqual(expectedSignature, signature))
{
throw new CryptographicException("The computed authentication value did not match the input");
}
return(data);
}