How to encrypt data using OFDM?

Hi

I have been assigned a task to encrypt data using OFDM. I used the following two techniques but I do not know if they are practically correct or not.

1. The signal is modulated using OFDM and passed through CDMA channel. 2. The signal is modulated using OFDM, compressed using LPC (plot attached).

Does any of the above ways imply that it's OFDM encryption? If no, then how it will be?

Thanks in advance.