  Fairly recently, a novel image encryption based on Arnold scrambling and
Lucas series has been proposed in the literature. The scheme design is based on
permutation-substitution operations, where Arnold map is used to permute pixels
for some T rounds, and Lucas sequence is used to mask the image and substitute
pixel's values. The authors of the cryptosystem have claimed, after several
statistical analyses, that their system is "with high efficiency" and resists
chosen and known plaintext attacks. Negatively, in this paper we showed the
opposite. The key space of the scheme under study could be reduced considerably
after our equivalent keys analysis, and thus the system is breakable under
reasonable brute force attack. After all, the design of the scheme has several
weaknesses that make it weak against chosen and known plaintext attacks.
Consequently, we do not recommend the use of this system for any cryptographic
concern or security purpose.
