[dfranke]

You can do better than that. Run the hash in HMAC mode, hash successive counter values to get a pseudorandom stream of bits. Xor your plaintext with the stream to get the ciphertext.

But how does biology contribute to any of this? At best, they've taken a known cryptographic algorithm and figured out how to implement it with the computation done in wetware. At worst, and I suspect the worst, they've simply observed that some parameters of their encoding scheme are tunable, and claiming that you have a secure cryptosystem if you keep those parameters secret.