[ackvastn] Biological cryptography

Implement public-key cryptography on a biological computer.

Perhaps using the above technology for evil, create a poison or pathogen for which deriving an antidote is cryptographically difficult even after the poison is isolated and function completely understood.  An antidote exists, and is easily synthesizable if one knows the private key.

Inspired by the morphogenic virus from Star Trek Deep Space 9, "Extreme Measures", which had a (only) 4-base DNA nucleotide sequence as a key, albeit with three fictional nucleotides.