The reason encryption requires randomness is not relevant to free will.

I don't see what you mean. Randomness is relevant to FW because determinism is, prima facie. (Compatibilists feel the need to argue that it in fact isn't, rather than taking it as obvious). Randomness is relevant to solving problems. A kind of FW that allows you to solve problems is worth having. If you want a more obviously relevant example, consider that evading a predator with random moves is more effective than adopting a potentially predictable "evasive pattern delta"