International Association
for Cryptologic Research

Differential Power Analysis (DPA) is a powerful technique for revealing secret data of cryptographic algorithms such as DES, AES and RSA implemented on a specific platform. In recent years, Correlation Power Analysis (CPA) allowed to better formalize the differential approaches of DPA with the use of a power model. We propose here two methods in order to optimize the power model for the targeted bits of the analysed algorithm. We will consider that all the targeted bits do not give the same contribution to the power consumption. Our first method consists in finding out the optimal ratio among the bits of a specific device. The second method is based on a statistical analysis of attack results while applying different possible ratios among the bits. The experimental electromagnetic radiation signals intercepted from an ASIC during DES operations show that our proposed methods allow to improve significantly the attack performance.

Cryptographic devices are vulnerable against the now well-known side channel leakage analysis. Secret data, such as keys, can be revealed by attacks like DPA, DEMA, CPA. However, this kind of attacks also exhibits wrong keys, this phenomenon being known as the "ghost peaks" problem and has been brie?y explained in CPA. We give here a comprehension and analysis of the ghost peak problem that occurs in differential analysis regarding to different power consumption model and various weighting techniques.