ABSTRACT: Encrypting procedures with multiplexed operations exhibit an inherent noise. We presented options to avoid background noise arising from the non-decoded images. We have a coding mask corresponding to each single input object, thus resulting in a static decrypting mechanism. Besides, if we manage the spatial destination of each decoded output, then we avoid the noise superposition. In those schemes, the displaying output order was irrelevant. However, when we face a sequence of events including multi-users, we need to develop another strategy. We present a multi-user encrypting scheme with a single encoding mask that removes the background noise, also showing the decrypted data in a prescribed sequence. The multiplexing scheme is based on the 4f double random phase encryption architecture and a theta modulation method, which consists in superposing each encrypted information with a determined sinusoidal grating. Afterwards we proceed to the completely encoded data multiplexing. In a multi-user scheme, we employ different encrypting masks in the 4f optical setup for each user, and the same mask is employed for the user sequence. We store the encrypted data in the single medium. After a Fourier transform operation and an appropriate filtering procedure, we reach the sequence of isolated encrypted spots corresponding to the right user. With the aid of the pertaining decoding mask, the user can decrypt the sequence. We avoid the noise by the appropriate choice of the modulating gratings pitch as to elude the overlapping of spots at the Fourier plane, which is the cause of information degradation.