CASCExplorer.KeyService.GetKey C# (CSharp) Method

        public static byte[] GetKey(ulong keyName)
        {
            byte[] key;
            keys.TryGetValue(keyName, out key);
            return key;
        }

        private static byte[] Decrypt(byte[] data, int index)
        {
            byte keyNameSize = data[1];

            if (keyNameSize == 0 || keyNameSize != 8)
            {
                throw new BLTEDecoderException("keyNameSize == 0 || keyNameSize != 8");
            }

            byte[] keyNameBytes = new byte[keyNameSize];
            Array.Copy(data, 2, keyNameBytes, 0, keyNameSize);

            ulong keyName = BitConverter.ToUInt64(keyNameBytes, 0);

            byte IVSize = data[keyNameSize + 2];

            if (IVSize != 4 || IVSize > 0x10)
            {
                throw new BLTEDecoderException("IVSize != 4 || IVSize > 0x10");
            }

            byte[] IVpart = new byte[IVSize];
            Array.Copy(data, keyNameSize + 3, IVpart, 0, IVSize);

            if (data.Length < IVSize + keyNameSize + 4)
            {
                throw new BLTEDecoderException("data.Length < IVSize + keyNameSize + 4");
            }

            int dataOffset = keyNameSize + IVSize + 3;

            byte encType = data[dataOffset];

            if (encType != ENCRYPTION_SALSA20 && encType != ENCRYPTION_ARC4) // 'S' or 'A'
            {
                throw new BLTEDecoderException("encType != 0x53 && encType != 0x41");
            }

            dataOffset++;

            // expand to 8 bytes
            byte[] IV = new byte[8];
            Array.Copy(IVpart, IV, IVpart.Length);

            // magic
            for (int shift = 0, i = 0; i < sizeof(int); shift += 8, i++)
            {
                IV[i] ^= (byte)((index >> shift) & 0xFF);
            }

            byte[] key = KeyService.GetKey(keyName);

            if (key == null)
            {
                throw new BLTEDecoderException("unknown keyname {0:X16}", keyName);
            }

            if (encType == ENCRYPTION_SALSA20)
            {
                ICryptoTransform decryptor = KeyService.SalsaInstance.CreateDecryptor(key, IV);

                return(decryptor.TransformFinalBlock(data, dataOffset, data.Length - dataOffset));
            }
            else
            {
                // ARC4 ?
                throw new BLTEDecoderException("encType A not implemented");
            }
        }