/// <summary>
/// Encrypts a message with an authentication tag and additional data using AES-GCM.
/// </summary>
/// <param name="message">The message to be encrypted.</param>
/// <param name="nonce">The 12 byte nonce.</param>
/// <param name="key">The 32 byte key.</param>
/// <param name="additionalData">The additional data; may be null, otherwise between 0 and 16 bytes.</param>
/// <returns>The encrypted message with additional data.</returns>
/// <remarks>The nonce should never ever be reused with the same key.</remarks>
/// <remarks>
/// The recommended way to generate it is to use GenerateNonce() for the first message, and increment it for each
/// subsequent message using the same key.
/// </remarks>
/// <exception cref="KeyOutOfRangeException"></exception>
/// <exception cref="NonceOutOfRangeException"></exception>
/// <exception cref="AdditionalDataOutOfRangeException"></exception>
/// <exception cref="CryptographicException"></exception>
public static byte[] Encrypt(byte[] message, byte[] nonce, byte[] key, byte[] additionalData = null)
{
//additionalData can be null
if (additionalData == null)
{
additionalData = new byte[0x00];
}
//validate the length of the key
if (key == null || key.Length != KEYBYTES)
{
throw new KeyOutOfRangeException("key", key == null ? 0 : key.Length,
string.Format("key must be {0} bytes in length.", KEYBYTES));
}
//validate the length of the nonce
if (nonce == null || nonce.Length != NPUBBYTES)
{
throw new NonceOutOfRangeException("nonce", nonce == null ? 0 : nonce.Length,
string.Format("nonce must be {0} bytes in length.", NPUBBYTES));
}
//validate the length of the additionalData
if (additionalData.Length > ABYTES || additionalData.Length < 0)
{
throw new AdditionalDataOutOfRangeException(
string.Format("additionalData must be between {0} and {1} bytes in length.", 0, ABYTES));
}
var cipher = new byte[message.Length + ABYTES];
var bin = Marshal.AllocHGlobal(cipher.Length);
long cipherLength;
var ret = SodiumLibrary.crypto_aead_aes256gcm_encrypt(bin, out cipherLength, message, message.Length,
additionalData, additionalData.Length, null,
nonce, key);
Marshal.Copy(bin, cipher, 0, (int)cipherLength);
Marshal.FreeHGlobal(bin);
if (ret != 0)
{
throw new CryptographicException("Error encrypting message.");
}
if (cipher.Length == cipherLength)
{
return(cipher);
}
//remove the trailing nulls from the array
var tmp = new byte[cipherLength];
Array.Copy(cipher, 0, tmp, 0, cipherLength);
return(tmp);
}
