Secrecy in Optics

MYRIAN TEBALDI; NÉSTOR BOLOGNINI; ROBERTO TORROBA

La Plata

Encuentro; Humboldt Kollege, “Argentine-Germany: A Century of Scientific Cooperation; 2011

Fundación Alexander von Humboldt

Protecting information from unauthorized users is the main task for encrypting methods. Optical processing, due to its inherent parallelism, represents an important alternative in this field. These optical methods are based on protecting the information to be transmitted by transforming the original data into white-noise data. Then, the signals should be hidden to human perception, keeping in consequence secret. The digital recording and processing allows the practical implementation with a reasonable quality. In all cases, the key codes should be difficult to find by chance and the decryption procedure should be relatively easy for receivers with the correct keys. To successfully retrieve the input information it is necessary not only to know the key code, but also to know the extra optical parameters. Then, the optical parameters (for instance polarization, wavelengths, etc) act as extra encryption keys, thus improving the robustness. Indeed, these optical parameters are suitable to store multiple encrypted images in a single recording medium in order to bring the chance for multiple users. In multiplexing arrangements, the encryption of an input image is associated to a determined status of the optical encrypting parameters. There exist a bi-univocal relation between each input image and its encrypted version. We can extend the idea to a single user with the capability of decoding a whole sequence of individually encrypted but associated events. This new concept thus involves the idea of encoding a dynamic situation. Besides, to retrieve the complete dynamic input information, it is necessary not only to properly decrypt the images but also to compose them in a synchronized way.