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

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.

► We reveal the collision property of interference-based optical image encryption scheme.
► We provide a method for avoiding the collision by adding an extra verification image.
► We demonstrate the effectiveness of our method by a set of computer simulations.