Optical encryption of sound signals

FABIAN MOSSO; MYRIAN TEBALDI; ROBERTO TORROBA; NÉSTOR BOLOGNINI

Lima

Conferencia; VII Ibero-American Conference on optics. X Latin-American Meeting on Optics, Lasers and Applications. RIAO-OPTILAS 2010; 2010

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 intwo 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 adetermined 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 bi-dimensionalencrypted image is transformed into a onedimensional 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.