Some time ago, a user named Steven uncovered a weakness in the FibonaRNG cipher, leading to this other post as a reply. At that time, I did not think that FibonaRNG needed to be strengthened, but recently I have realized that it would not be very difficult to remove that weakness. The result is PolyCrypt. The “Poly” bit comes from the fact that it can not only add security, but also remove it, making it a good platform to test classic human-computable ciphers.