public byte[] DecryptBlock(NewCamdMessageType type, byte[] data)
{
var channel = (data[18] << 8) + data[19];
var channelBlock = GetChannelById(channel);
if (channelBlock == null)
{
_logger.Warn($"No valid block found for channel {channel}");
return(new byte[0]);
}
var block1 = _crypto.AesDecrypt(data.Skip(24).Take(16).ToArray(), channelBlock.Key);
var block2 = _crypto.AesDecrypt(data.Skip(40).Take(16).ToArray(), channelBlock.Key);
var block3 = _crypto.AesDecrypt(data.Skip(56).Take(16).ToArray(), channelBlock.Key);
if (!Encoding.ASCII.GetString(block1).StartsWith("CEB", StringComparison.Ordinal))
{
_logger.Warn($"Failed to decrypt block for channel {channel}");
return(new byte[0]);
}
_logger.Info($"Decryption of channel {channel} succeeded");
var key1 = block1.Skip(9).Take(7).Concat(block2).Concat(block3.Take(9));
var key2 = block2.Skip(9).Take(7).Concat(block3.Take(9));
return(type == NewCamdMessageType.MsgKeyblockReq1 ?
key1.Concat(key2).ToArray() :
key2.Concat(key1).ToArray());
}