Design Space Exploration of a Reconfigurable HMAC-Hash Unit

In this paper, a design space exploration of a reconfigurable HMAC-hash unit is discussed. This unit implements one of six standard hash algorithms, namely, MD5, SHA-1, RIPEMD-160, HMAC-MD5, HMAC-SHA-1, and HMAC-RIPEMD-160. The design space exploration of this unit is done using the Handel-C language. We propose key reuse mechanism for successive messages in order to improve the HMAC throughput. In addition, we explore the design space by providing two implementations of the HMAC algorithm, one for a general key size and another for a fixed key size. In each implementation, we use standard key use and the proposed key reuse mechanisms, and that results in four different implementations. The performance of these four implementations is analyzed with respect to three design metrics: area, delay, and throughput. We found that the proposed key reuse mechanism improves the HMAC throughput significantly when a large key is reused, with negligible increase in area and delay. In addition, we found that the implementation of HMAC for fixed key size is better in area, delay, and throughput than the HMAC implementation for general key size.