Analysis and hardware implementation of synchronization methods for stream ciphers

Huang, Yaping (2010) Analysis and hardware implementation of synchronization methods for stream ciphers. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (8MB)

Abstract

In this thesis, we investigate two synchronization methods for stream ciphers. The first is statistical cipher feedback (SCFB) mode, which is a recently proposed mode of operation for block ciphers. The other is the marker-based mode, which is the synchronous stream cipher using "marker" to regain synchronization. SCFB mode is a hybrid of OFB mode and CFB mode; hence, it has a high throughput and the capability of self-synchronizing. The marker-based synchronous stream cipher is also able to obtain synchronization under limited circumstances. -- In this thesis, SCFB mode and the marker-based mode are both implemented in digital hardware targeting the FPGA technology. The device we have used is the Xilinx Spartan-3E FPGA. Commonly, SCFB mode is implemented by using the block cipher, AES, as the keystream generator; however, in our research, we use the stream cipher, Grain-128, as the keystream generator for SCFB mode implementation. The designed system structure and synthesis results of the two modes are given in this thesis. Throughout our research, VHDL code and Modelsim PE Student Edition 6.5d are used to design and simulate the functionality of our systems. The behavior level description is synthesized by using Xilinx ISE Webpack 10.1 tool and the .bit stream which is used to configure FPGA board is generated. The designed system is run on the Digilent Nexys II FPGA board and tested. To download the .bit stream on to the FPGA board and transfer data between the computer and FPGA, the Digilent Adept Suite tool is used. -- Through the FPGA hardware implementation, we obtain that SCFB mode configured for a stream cipher, Grain-128, can run at the speed of 89Mbps on a real FPGA and an efficiency of SCFB mode is 100%. The marker-based mode can reach the speed of 113 Mbps and has an efficiency of 94%. Although the system of marker-based mode is a little faster and has less hardware complexity than SCFB mode, it is limited in its synchronization recovery. In contrast, SCFB mode can regain synchronization for any number of bit slips. Hence, SCFB mode is more suitable for high speed physical layer security. -- The performance analysis of SCFB mode and marker-based mode is also provided with respect to characteristics of synchronization recovery delay (SRD) and error propagation factor (EPF). In particular, through the simulation of SRD and EPF versus varying sync patterns, we have found the best sync pattern format for SCFB mode. The best sync patterns are uncorrelated, that is, the shifted version of the sync pattern do not match the bits from the original sync pattern. In our research, we have used the sequence "10000000" as the sync pattern for SCFB mode implementation and as the marker for marker-based synchronous stream cipher implementation.

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