Abstract
The stream cipher TPypy has been designed by Biham and Seberry in January 2007 as the strongest member of the Py-family ciphers, after weaknesses in the other members Py, Pypy, Py6 were discovered. One main contribution of the paper is the detection of related-key weaknesses in the Py-family of ciphers including the strongest member TPypy. Under related keys, we show a distinguishing attack on TPypy with data complexity 2192.3 which is lower than the previous best known attack on the cipher by a factor of 288. It is shown that the above attack also works on the other members TPy, Pypy and Py. A second contribution of the paper is design and analysis of two fast ciphers RCR-64 and RCR-32 which are derived from the TPy and the TPypy respectively. The performances of the RCR-64 and the RCR-32 are 2.7 cycles/byte and 4.45 cycles/byte on Pentium III (note that the speeds of the ciphers Py, Pypy and RC4 are 2.8, 4.58 and 7.3 cycles/byte). Based on our security analysis, we conjecture that no attacks lower than brute force are possible on the RCR ciphers.
This work was supported in part by the Concerted Research Action (GOA) Ambiorics 2005/11 of the Flemish Government, by the IAP Programme P6/26 BCRYPT of the Belgian State (Belgian Science Policy), and in part by the European Commission through the IST Programme under Contract IST-2002-507932 ECRYPT. The first author is supported by an IWT SoBeNeT project. The second author is supported by an IBBT (Interdisciplinary Institute for Broadband Technology) project. The information in this document reflects only the authors’ views, is provided as is and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and liability.
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Sekar, G., Paul, S., Preneel, B. (2007). Related-Key Attacks on the Py-Family of Ciphers and an Approach to Repair the Weaknesses. In: Srinathan, K., Rangan, C.P., Yung, M. (eds) Progress in Cryptology – INDOCRYPT 2007. INDOCRYPT 2007. Lecture Notes in Computer Science, vol 4859. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-77026-8_6
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