Construcción de un cifrador basado en una permutación pseudo-aleatoria
(Castañeda Marín, Hernando y Rodríguez Graterol, Wladimir)

The purpose of this paper is the analysis and development of as practical implementation of a cipher based on the schema proposed by Even and Mansour[1]. The schema corresponds to a block cipher based in the use of a permutation in the encryption operation and in the corresponding inverse function for the decryption process. The key K that consist in two sub keys K₁ and K₂, which are produce by means of a pseudorandom numbers generator with unpredictable inputs and pseudorandom output sequences. To measure the reliability of the permutation of the resulting sequence of the previous XOR operation, hypothesis test were done using the statistic X² for different combinations of the { 0,1 } patterns referenced in those sequences. In order to reach this purpose the Yarrow-160, a visual C++ software from Counterpane System, computational tool was used; extended with the necessary encryption and decryption routines for the proposed cryptosystem based on the Even and Mansour schema. Also a routine was added, that allows doing statistical test by determining the computed values of X² for the different combinatorial patterns of the sequences. This work is an academicals practice to test the strengths and debilities of the Counterpane System software and allows to extend it by means of the construction of a cipher based on a simple permutation that, as practical implementation allows the test of its computational complexity and security. The realization of a cryptanalysis and the realization of different cryptographic attacks will made possible future works in the field of cryptographic and computational security.

Ponencia dictada en: XXXI Conferencia Latinoamericana de Informática - CLEI2005.
Cali-Colombia, del 10 al 14 de octubre de 2005.