A system for interference-based optical multiple binary image encryption by random phase mask multiplexing is proposed. The encryption process is realized digitally and the decryption process can be completed optically or digitally. Multiple binary images can be analytically hidden into two phase only masks (POMs). For decryption, the diffraction filed of the two POMs are superposed by utilizing the beam splitters to form a complex field, then the complex field is further modulated by the private key, as a result of which the original plaintext assosicated with the private key is retrieved. The regenerated image can be directly recorded by CCD camera. The encryption algorithm for this new method is quite simple and does not need iterative encoding. In addition, the decryption system is easy to be realized physically. The multiplexing capacity is analyzed through the correlation coefficient. Computer simulation results confirm the validity of the proposal.