Does Physical Security of Cryptographic Devices Need a Formal Study?

François-Xavier Standaert, UCL Crypto Group, Belgian Fund for Scientific Research (FNRS), Brussels, Belgium

Abstract: Traditionally, cryptographic algorithms provide security against an adversary who has only black box access to cryptographic devices. That is, the only thing the adversary can do is to query the cryptographic algorithm on inputs of its choice and analyze the responses, which are always computed according to the correct original secret information. However, such a model does not always correspond to the realities of physical implementations. During the last decade, significant attention has been paid to the physical security evaluation of cryptographic devices. In particular, it has been demonstrated that actual attackers may be much more powerful than what can be captured by the black box model. They can actually get a side-channel information, based on the device physical computational steps. A large set of practical techniques for breaking and repairing (i.e., applying countermeasures) have been found in this area of physical security and further, the area is now an important part of crypto-engineering.

The issue that will be addressed in this talk is: Do we need more fundamental (perhaps more theoretical) study of the area? For this purpose, I'll start by discussing the motivations for the development of formal tools in the analysis of cryptographic hardware devices and side-channel attacks. From these motivations, I'll describe a recently introduced framework that concentrates on two important issues in physically observable cryptography, namely: (1) how to compare different leaking implementations? and (2) how to compare different side-channel adversaries. Based on practical examples, I'll highlight both the limitations in the answers one can provide to solve these questions and the advantages of a sound modeling compared to present ad hoc approaches for the evaluation of side-channel attacks. The talk will be divided in two parts in order to be accessible for a large audience. The first part will introduce side-channel attacks and the motivations for a formal model that captures them. The second part will investigate specific issues and results in the modeling of side-channel attacks. A particular attention will be paid to the statistical tools necessary for the application of the proposed framework to actual (simulated or experimental) leakage traces.

About the speaker: François-Xavier Standaert was born in Brussels, Belgium in 1978. He received the Electrical Engineering degree and PhD degree from the Université Catholique de Louvain, respectively in June 2001 and June 2004. In 2004-2005, he was a Fulbright visiting researcher at Columbia University, Department of Computer Science, Network Security Lab (September 04 to February 05) and at the MIT Medialab, Center for Bits and Atoms (February 05 to July 05). In March 2006, he was a founding member of IntoPIX  s.a. He is now an associate researcher of the Belgian Fund for Scientific Research (FNRS) at the UCL Crypto Group. His research interest includes digital electronics and FPGAs, cryptographic hardware, design of symmetric cryptographic primitives, physical security isssues and side-channel analysis.