Développement et implémentation des techniques de cryptage des données basées sur les transformées discrètes

Abstract

In this thesis, we present two contributions in image encryption domain. In the first contribution, we propose a novel opto-digital image encryption technique by introducing a new recursive non-linear pre-encryption. This is significant because the proposed pre-encryption-based DRPE differs from the existing scrambling-based DRPE versions not only for its non-linearity property, but also for its recursive property that ensures the accumulation and propagation of the error to all pixels in the case of any wrongness in the decryption key. In addition the key sensitivity of the proposed technique is significantly improved compared to that of the existing DRPE-based techniques. In the second contribution, we propose the use of the symmetry that exists in the parametric Fourier transform, by its application in the field of encryption of the fixed images in the frequency domain. This property allows us to send a single image instead of two (real part and imaginary part), this is done by a simple complex to real conversion, which is also reversible. This is significant because this technique reduces the storage space and the capacity of the transmission and significantly increases the robustness compared to the existing techniques