Collision in optical image encryption based on interference and a method for avoiding this security leak

TLDR: A study of the collision property of the optical image encryption technique based on interference is presented and an efficient way to avoid this potential risk is provided by adding an extra unit in the original structure, which can be called a double-factor verification system.

Abstract: From the perspective of cryptography, collision is an undesirable situation that occurs when two or more distinct inputs into a security system produce undistinguishable outputs. In this paper we present a study of the collision property of the optical image encryption technique based on interference (Zhang et al. Optics Letters; 2008:33(21)). For an arbitrary secret image (output) to be encrypted, we can find various distinct pairs of phase-only masks (inputs), which yield almost the same outputs by use of a modified phase retrieval algorithm. Meanwhile, we also provide an efficient way to avoid this potential risk by adding an extra unit in the original structure, which can thus be called a double-factor verification system. A series of computer simulations were also carried out to demonstrate our concern and strategy.