An optical hybrid cryptosystem based on diffraction-pattern-like ciphertext

The existing optical cryptosystems always process the plaintexts into a random noise image, and the length of the key in the encryption progress is generally much longer than that of the plaintext. In this work, a Harr-wavelet-based optical cryptosystem using the convex lens is proposed. This scheme only needs recording the amplitude. The encryption key includes a series of parameters which is quite shorter than the length of the plaintext. These keys are natural inherent parameters. The Harr transform is introduced to improve the sensibilities of encryption keys and reduce the length of the ciphertexts. The ciphertext is a diffraction-pattern-like image which contains no information of plaintext. Besides, the cost of the whole optical encryption is reduced heavily. Extensive numerical simulations are carried out to verify the security, feasibility, and sensibilities of encryption keys of the proposed encryption scheme. In addition, how to properly select encryption keys is also discussed.