Complex sentence: In Kari's proposal, the cellular automaton rule would be the encryption key, encryption would be performed by running the rule forward one step, and decryption would be performed by running it backward one step.
Split into simpler sentences: In Kari's proposal, the cellular automaton rule would be the encryption key. Encryption would be performed by running the rule forward one step, and decryption would be performed by running it backward one step.