Plaintext Recovery in DES-like Cryptosystems Based on S-boxes with Embedded Parity Check

We describe an approach for recovering the plaintext in block ciphers having a design structure similar to the Data Encryption Standard but with improperly constructed S-boxes. The experiments with a backtracking search algorithm performing this kind of attack against modified DES/Triple-DES in ECB mode show that the unknown plaintext can be recovered with a small amount of uncertainty and this algorithm is highly efficient both in time and memory costs for plaintext sources with relatively low entropy. Our investigations demonstrate once again that modifications resulting to S-boxes which still satisfy some design criteria may lead to very weak ciphers. ACM Computing Classification System (1998): E.3, I.2.7, I.2.8.This work was presented in part at the 1-st International Conference Bulgarian Cryptography Days 2012, Sofia, Bulgaria, 20–21 September 2012

LA CRIPTOGRAFÍA DIPLOMÁTICA MEXICANA EN LA PRIMERA MITAD DEL SIGLO XIX. TRES EJEMPLOS

Descripciones y análisis de tres ejemplos de la criptografía diplomática que se usó en México entre 1824 y 1830Descriptions and analyses of three kinds of cryptosystems that Mexican diplomats used between the years 1824 and 183