A novel, to the best of our knowledge, color computational ghost imaging scheme is presented for the reconstruction of a color object image, which greatly simplifies the experimental setup and shortens the acquisition time. Compared to conventional schemes, it only adopts one digital light projector to project color speckles and one single-pixel detector to receive the light intensity, instead of utilizing three monochromatic paths separately and synthesizing the three branch results. Severe noise and color distortion, which are common in ghost imaging, can be removed by the utilization of a generative adversarial network, because it has advantages in restoring the image’s texture details and generating the image’s match to a human’s subjective feelings over other generative models in deep learning. The final results can perform consistently better visual quality with more realistic and natural textures, even at the low sampling rate of 0.05.

Attack techniques on a cryptosystem include not only cryptanalysis, but also forgery and modification of messages, deception and confusion on both sender and receiver sides, and so on. In this Letter, we show that an optical encryption system based on computational ghost imaging (CGI) has security vulnerability owing to its high tolerance for error deviation of ciphertext. It leaves a chance for a forgery attack in which attackers can forge a set of fake keys according to the intercepted ciphertext. If the forged key can be transmitted to the receiver by some disguised means, he/she may be cheated or confused by the retrieved fake images. The discovery of this vulnerability may also help upgrade the CGI-based encryption system.

A multiple-image encryption (MIE) scheme with a single-pixel detector has been proposed according to the principle of ghost imaging. In this scheme, each of the spatially coherent laser beams is modified by a set of phase-mask keys and illuminates on a secret image. All of the transmitted lights are recorded together by a single-pixel (bucket) detector to obtain a ciphertext, but anyone of the secret images can be decrypted from the ciphertext independently without any mutually overlapped despite some noise in them. The MIE scheme will bring convenience for data storage and transmission, especially in the case that different secret images need to be distributed to different authorized users, because the ciphertext is a real-valued function and this scheme can effectively avoid the secret images being extracted mutually. The basic principle of the MIE scheme is described theoretically and verified by computer simulations. Finally, the feasibility, robustness and encryption capacity are also tested numerically.