Evidence of signatures associated with cryptographic modes of operation isestablished. Motivated by some analogies between cryptographic and dynamicalsystems, in particular with chaos theory, we propose an algorithm based onLyapunov exponents of discrete dynamical systems to estimate the divergenceamong ciphertexts as the encryption algorithm is applied iteratively. Theresults allow to distinguish among six modes of operation, namely ECB, CBC,OFB, CFB, CTR and PCBC using DES, IDEA, TEA and XTEA block ciphers of 64 bits,as well as AES, RC6, Twofish, Seed, Serpent and Camellia block ciphers of 128bits. Furthermore, the proposed methodology enables a classification of modesof operation of cryptographic systems according to their strength.
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