Computer Science & Engineering: An International Journal (CSEIJ), Vol.3, No.1, February 2013 DOI : 10.5121/cseij.2013.3101 1 THROUGHPUT/AREA TRADE-OFFS OF LOOP- UNROLLING,FUNCTIONAL, AND STRUCTURAL PIPELINE FOR SKEIN HASH FUNCTION George S. Athanasiou 1 , Elias Tsingkas 1 , Harris E. Michail 2 , George Theodoridis 1 and Costas E. Goutis 1 1 Department of Electrical and Computer Engineering, University of Patras, Greece gathanas@ece.upatras.gr 2 Department of Electrical Engineering, Computer Engineering and Informatics, Cyprus University of Technology, Limassol, Cyprus ABSTRACT In this paper, a design space exploration is performed aiming at developing high-performance hardware architectures for the new cryptographic hash function Skein-512. Three well-known design optimization techniques namely, the loop unrolling, the structural and functional pipeline, are applied, while several design alternatives have been explored to derive optimized FPGA implementations. The proposed architectures have been implemented and evaluated in three Xilinx technologies (Virtex-4, Virtex-5, and Virtex-6). Based on the experimental results, when all the three techniques are applied, the best architecture is the 8-round_unroll one with two functional and three structural pipeline stages. To the best of the authors’ knowledge, it is the first time that all these three techniques are studied and exploited together for the Skein algorithm. Also, the proposed architectures outperform the corresponding existing ones in terms of Throughput/Area factor from 27% up to 192%, respectively. KEYWORDS Security, Authentication, Hash functions, Skein, FPGA 1. INTRODUCTION 21st century is considered to be the era of mass communication and electronic information exchange. However, this advancement goes in parallel with serious considerations regarding the security of the exchanged information, especially when this information is sensitive and/or confidential. To overcome this problem, advanced security mechanisms are included in modern communication protocols as well as in data transmission and communication systems. Typical examples are the encryption and authentication which are performed in every transmitted data packet by the forthcoming Internet Protocol version 6 (IPv6) [1] via the Internet Protocol Security (IPSec) [2]. Regarding authentication, which is an important feature of IPSec, it is realized using a standard hash algorithm [3]. Beyond that, hash functions are among the crucial building blocks of many popular security systems and applications like Secure Electronic Transactions (SET) [4], IEEE 802.16 standard [5] for Local and Metropolitan Networks, digital signature schemes [6] and web protocols [7]. Skein [10], [17] is a new cryptographic hash function, introduced in the end of 2010. It combines speed, security, simplicity, and a great deal of flexibility in a modular package that is easy to