Optical encryption of sound signals

FABIÁN MOSSO; MYRIAN TEBALDI; ROBERTO TORROBA; NESTOR BOLOGNINI

Lima

Congreso; VII Reunión Iberoamericana de Óptica (VII RIAO) y X Encuentro Latinoamericano de Óptica, Láseres y sus Aplicaciones (X OPTILAS); 2010

Pontificia Universidad Católica del Perú

We present a procedure to encrypt sound signals by employing a conventional 4f optical system. A one-dimensional sound signal is rearranged into a bi-dimensional array, which is finally encrypted in the 4f system. The random phase keys employed in the 4f system are generated by affine transformations. The random phase masks are characterized by the appropriate affine parameters in order to design a controlled random distribution associated to each phase mask. With this purpose, we chose an amplitude image source that is divided in two equal images to which the affine transformations are applied. The transformed images are added on a modular basis obtaining a final random amplitude distribution. These amplitude random distributions are mapped to pure phase masks by assigning to each amplitude level a determined phase value. In the input of the 4f system is allocated the bi-dimensional array and one of the pure random phase masks is attached. The system is illuminated by a plane wave producing the Fourier transform of the input, which is multiplied by a second random phase mask. Finally, a second Fourier transform produces the encrypted image. This bidimensional encrypted image is transformed into a one-dimensional array that constitutes the encrypted sound signal. In order to decrypt the encoded information, we reconvert it into a bi-dimensional array. Now we use this array as the input of the 4f system. By using the correct phase mask generated by the exact affine transformation parameters, the original information is recovered and the sound signal is deciphered. We present experimental results that confirm the proposal.