LFSR Stream Cipher

The same XOR operation performs encryption and decryption.

Behavior

• load_seed loads the seed; a zero seed is replaced with 8'h01.
• When enable=1, data_out = data_in XOR LFSR_state and valid pulses.
• After each byte, the LFSR advances using taps 7, 5, 4, and 3.