Analysis and implementation of statistical cipher feedback mode and optimized cipher feedback mode

Yang, Fang (2004) Analysis and implementation of statistical cipher feedback mode and optimized cipher feedback mode. Masters thesis, Memorial University of Newfoundland.

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Abstract

In this thesis, two recently proposed modes of operation for block ciphers, referred to as statistical cipher feedback (SCFB) mode and optimized cipher feedback (OCFB) mode, are investigated. Both cipher modes can achieve the capability of selfsynchronization to recover from bit slips or insertions in the communication channel automatically. Compared to CFB mode, both cipher modes can obtain higher efficiency with modest buffer size and reasonable latency. Hence, both modes can be applied to high-speed digital hardware implementation and they have been identified as being suitable for physical layer security for applications such as SONET/SDH. In this thesis, both modes are implemented in software and hardware. In particular, the hardware structure and method of hardware implementation are investigated. Parallel and serial transfers are applied to the hardware implementation of SCFB mode and OCFB mode, respectively. Very High Speed Integrated Circuit Description Language (VHDL) and LSI design with 0.18 CMOS technology supported by Canadian Microelectronics Corporations (CMC) are used in the process of hardware implementation. The hardware structures of both modes are synthesized by using Synopsis tools provided by CMC as well. In addition, the performances of both modes are analyzed with respect to characteristics such as the theoretical efficiency, synchronization recovery delay, and the error propagation factor. Furthermore, the relationship between efficiency, probability of queue overflow, and buffer size is investigated. It is definite that both of modes can obtain higher efficiency than cipher feedback mode. OCFB mode performs marginally better with respect to error propagation and synchronization recovery delay in some circumstances. SCFB mode is able to achieve higher efficiency with a given buffer size and probability of buffer overflow in an efficient hardware implementation. Similarly, for a given efficiency and buffer size, SCFB mode has a lower probability of buffer overflow than OCFB mode. In fact, while for SCFB it is possible to guarantee no overflow with 50% efficiency and a buffer size equal to the block size, it is not possible to guarantee no overflow for efficiencies that are much less than 50% for OCFB mode. These results imply that SCFB is a mode more suitable for high speed physical layer security than OCFB mode.

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