Encryption Decryption Question:

LUC is a public-key cryptosystem developed by a group of researchers in Australia and New Zealand. The cipher implements the analogs of ElGamal, Diffie-Hellman, and RSA over Lucas sequences. LUCELG is the Lucas sequence analog of ElGamal, while LUCDIF and LUCRSA are the Diffie-Hellman and RSA analogs. Lucas sequences used in the cryptosystem are the general second-order linear recurrence relation defined by