private static byte[] XChaCha20Poly1305(bool isEncryption, byte[] key, byte[] nonce, byte[] message, byte[] aad = null)
{
if (key.Length != 32)
{
throw new ArgumentException("Key must be 32 bytes", nameof(key));
}
if (nonce.Length != 24)
{
throw new ArgumentException("Nonce must be 24 bytes", nameof(nonce));
}
// subkey (hchacha20(key, nonce[0:15]))
var subkey = HChaCha20.CreateSubkey(key, nonce); // TODO: parse nonce bytes to pass through here instead
// nonce (chacha20_nonce = "\x00\x00\x00\x00" + nonce[16:23])
var chaChaNonce = new byte[12];
Array.Copy(new byte[] { 0, 0, 0, 0 }, chaChaNonce, 4);
Array.Copy(nonce, 16, chaChaNonce, 4, 8);
// chacha20_encrypt(subkey, chacha20_nonce, plaintext, blk_ctr)
var outputLength = message.Length;
if (isEncryption)
{
outputLength += 16;
}
else
{
outputLength -= 16;
}
var output = new byte[outputLength];
var keyMaterial = new KeyParameter(subkey);
var parameters = new ParametersWithIV(keyMaterial, chaChaNonce);
var chaCha20Poly1305 = new ChaCha20Poly1305();
chaCha20Poly1305.Init(isEncryption, parameters);
// if aditional data present
if (aad != null)
{
chaCha20Poly1305.ProcessAadBytes(aad, 0, aad.Length);
}
var len = chaCha20Poly1305.ProcessBytes(message, 0, message.Length, output, 0);
chaCha20Poly1305.DoFinal(output, len);
return(output);
}
public static byte[] Encode(byte[] input, byte[] key, byte[] nonce)
{
var subNonce = new byte[12];
if (nonce.Length == 24)
{
var hNonce = new byte[16];
System.Buffer.BlockCopy(nonce, 0, hNonce, 0, 16);
System.Buffer.BlockCopy(nonce, 16, subNonce, 4, 8);
key = HChaCha20.Encode(key, hNonce);
}
else if (nonce.Length == 12)
{
System.Buffer.BlockCopy(nonce, 0, subNonce, 0, 12);
}
else
{
throw new System.ArgumentException();
}
return(NormalEncode(input, key, subNonce));
}