Improved decryption quality with a random reference beam cryptosystem

The secure managing of sensible data is one of the main challenges nowadays. During the last years several advances have demonstrated the ability of optical encrypting systems to protect information. In spite of these developments, there are some evident issues to be solved. One of the main concerns is the limitation of the experimental cryptosystems in the size of the inputs that can be properly protected and recovered by the encrypting system. In the case of the experimental joint transform correlator (JTC) cryptosystem, the data to be encoded and the key are placed side by side in the input plane. Therefore, the size of the object to be encrypted is limited by the size of the encryption key and the separation between the input and the key. This limitation leads to degradation on the recovered data according the size and the spatial frequencies content of the object for a given recording media. In this work we experimentally implement an interferometric cryptosystem in which the encryption key is a ground glass diffuser (GGD) located in the reference arm. In the object arm, the information to be encoded is displayed in a spatial light modulator (SLM) and placed in contact with another GGD. This system allows the projection of the input object in the whole SLM area. The encryption process results from the interference between the reference beam and the Fourier transform of the input object plane. We experimentally analyze the quality of the decrypted object in relation with the size of the input original object. Then, we compare the performance of this system with the JTC cryptosystem. Finally, we implement a protocol for a multi-user environment under the rotation of the key. Experimental results show the viability, versatility and applicability of the proposal.