/// <summary>
/// Decrypts a cipher with an authentication tag and additional data.
/// </summary>
/// <param name="cipher">The cipher to be decrypted.</param>
/// <param name="nonce">The 8 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 decrypted cipher.</returns>
/// <exception cref="KeyOutOfRangeException"></exception>
/// <exception cref="NonceOutOfRangeException"></exception>
/// <exception cref="AdditionalDataOutOfRangeException"></exception>
/// <exception cref="CryptographicException"></exception>
public ArraySegment <byte> Decrypt(ArraySegment <byte> cipher, byte[] nonce, byte[] key, ArraySegment <byte> additionalData)
{
//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));
}
//additionalData can be null
GCHandle hAddData;
IntPtr pAddData;
int adataLength;
if (additionalData.Array == null)
{
hAddData = GCHandle.Alloc(Array.Empty <byte>(), GCHandleType.Pinned);
pAddData = hAddData.AddrOfPinnedObject();
adataLength = 0;
}
else
{
hAddData = GCHandle.Alloc(additionalData.Array, GCHandleType.Pinned);
pAddData = hAddData.AddrOfPinnedObject() + additionalData.Offset;
adataLength = additionalData.Count;
}
// //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 message = _bufferPool.Rent(cipher.Count - ABYTES);
var hMsg = GCHandle.Alloc(message, GCHandleType.Pinned);
var hCipher = GCHandle.Alloc(cipher.Array, GCHandleType.Pinned);
var ret = SodiumLibrary.crypto_aead_xchacha20poly1305_ietf_decrypt(hMsg.AddrOfPinnedObject(),
out long messageLength, null, hCipher.AddrOfPinnedObject() + cipher.Offset, cipher.Count,
pAddData, adataLength, nonce, key);
hMsg.Free();
hAddData.Free();
hCipher.Free();
if (ret != 0)
{
throw new CryptographicException("Error decrypting message.");
}
return(new ArraySegment <byte>(message, 0, (int)messageLength));
}
/// <summary>
/// Decrypts a cipher with an authentication tag and additional data using XChaCha20-Poly1305.
/// </summary>
/// <param name="cipher">The cipher to be decrypted.</param>
/// <param name="nonce">The 24 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 decrypted cipher.</returns>
/// <exception cref="KeyOutOfRangeException"></exception>
/// <exception cref="NonceOutOfRangeException"></exception>
/// <exception cref="AdditionalDataOutOfRangeException"></exception>
/// <exception cref="CryptographicException"></exception>
public static byte[] Decrypt(byte[] cipher, 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 message = new byte[cipher.Length - ABYTES];
var bin = Marshal.AllocHGlobal(message.Length);
long messageLength;
var ret = SodiumLibrary.crypto_aead_xchacha20poly1305_ietf_decrypt(bin, out messageLength, null, cipher, cipher.Length,
additionalData, additionalData.Length, nonce, key);
Marshal.Copy(bin, message, 0, (int)messageLength);
Marshal.FreeHGlobal(bin);
if (ret != 0)
{
throw new CryptographicException("Error decrypting message.");
}
if (message.Length == messageLength)
{
return(message);
}
//remove the trailing nulls from the array
var tmp = new byte[messageLength];
Array.Copy(message, 0, tmp, 0, (int)messageLength);
return(tmp);
}
