A cascaded-phases retrieval algorithm that synthesizes the target image into two random phase-masks(RPM) was proposed for image encryption.This proposed algorithm employs a searching strategy that modifies both the distributions of the two RPM simultaneously to enlarge the searching space.Consequently,a retrieved image with significantly high quality was obtained.Computer simulation results show that the algorithm converges rapidly,that is,the closely optimized solution can be found very quickly.The significant image can be obtained only when the designed RPM are matched and each of them is located into the proper plane in the 4-f architecture.This character may introduce a high level of security.