Collision in double random phase encoding

Collision is a situation that occurs when two or more distinct inputs into a security system produce identical outputs, which is undesirable in some security applications. This is especially true of the applications of watermarking and authentication. In this manuscript we present a study of the collision property of double random phase encoding. We show that one can produce meaningful collisions from the cyphertext of a watermark embedded in a host image by use of phase retrieval techniques.