Preaveraging and Carry Propagate Approaches to Side-Channel Analysis of HMAC-SHA256

Although HMAC-SHA has been standardized for over a decade, few published attacks on the single-cycle round implementation exist. In this research, new attack techniques are provided, for the first time, (1) to help to discriminate between values of secret intermediate variables within HMAC and (2) to reduce the large word size complexity. Preaveraging and carry propagate techniques are proposed using chosen plaintexts and shown to significantly reduce the complexity and runtimes for side-channel analysis of an Altera FPGA platform. This research is important for advancing side channel analysis of complex embedded ASICs and ensuring secure implementations in future embedded ubiquitous devices.