Abstract: Based on the traditional double-random phase optical encryption system, a new single-intensity-recording optical encryption technology was proposed. In the encryption process, the original image was placed on the input plane of 4-f system to have a double random phase encryption. Using CCD sensitization devices, only the intensity distribution on the output plane was recorded as ciphertext. The optical encryption process only needed one exposure. In the decryption process, the original image could be retrieved from the ciphertext using phase retrieval algorithm. Since the decryption process used digital method, a variety of digital image processing technology could be introduced in the decryption process to suppress speckle noise, so as to further improve the decrypted image quality. Through a series of simulation experiments, it is proved that the proposed encryption system can be used for binary image and grayscale image encryption. Moreover, it can well resist known plaintext attack and chosen plaintext attack. Theoretical analysis and computer simulations show that this optical encryption system is simple in structure, easy to achieve, invulnerable to various attacks and of high security.