Advanced cryptographic system : design, architecture and FPGA implementation

Abstract

The field programmable gate array (FPGA) is a powerful technology, and since its introduction broad prospects have opened up for engineers to creatively design and implement complete systems in various fields. One such area that has a long history in information and network security is cryptography, which is considered in this thesis. The challenge for engineers is to design secure cryptographic systems, which should work efficiently on different platforms with the levels of security required. In addition, cryptographic functionalities have to be implemented with acceptable degrees of complexity while demanding lower power consumption. The present work is devoted to the design of an efficient block cipher that meets contemporary security requirements, and to implement the proposed design in a configurable hardware platform. The cipher has been designed according to Shannon’s principles and modern cryptographic theorems. It is an iterated symmetric-key block cipher based on the substitution permutation network and number theoretic transform with variable key length, block size and word length. These parameters can be undisclosed when determined by the system, making cryptanalysis almost impossible. The aim is to design a more secure, reliable and flexible system that can run as a ratified standard, with reasonable computational complexity for a sufficient service time. Analyses are carried out on the transforms concerned, which belong to the number theoretic transforms family, to evaluate their diffusion power, and the results confirm good performance in this respect mostly of a minimum of 50%. The new Mersenne number transform and Fermat number transform were included in the design because their characteristics meet the basic requirements of modern cryptographic systems. A new 7×7 substitution box (S-box) is designed and its non-linear properties are evaluated, resulting in values of 2-6 for maximum difference propagation probability and 2-2.678 for maximum input-output correlation. In addition, these parameters are calculated for all S-boxes belonging to the previous and current standard algorithms. Moreover, three extra S-boxes are derived from the new S-box and another three from the current standard, preserving the same non-linear properties by reordering the output elements. The robustness of the proposed cipher in terms of differential and linear cryptanalysis is then considered, and it is proven that the algorithm is secure against such well-known attacks from round three onwards regardless of block or key length. A number of test vectors are run to verify the correctness of the algorithm’s implementation in terms of any possible error, and all results were promising. Tests included the known answer test, the multi-block message test, and the Monte Carlo test. Finally, efficient hardware architectures for the proposed cipher have been designed and implemented using the FPGA system generator platform. The implementations are run on the target device, Xilinx Virtex 6 (XC6VLX130T-2FF484). Using parallel loop-unrolling architecture, a high throughput of 44.9 Gbits/sec is achieved with a power consumption of 1.83W and 8030 slices for implementing the encryption module with key and block lengths of 16×7 bits. There are a variety of outcomes when the cipher is implemented on different FPGA devices as well as for different block and key lengths.