Abstract. In a recent work, Mangard et al. showed that under certain assumptions, the (so-called) standard univariate side-channel attacks using a distance-of-means test, correlation analysis and Gaussian templates are essentially equivalent. In this paper, we show that in the context of multivariate attacks against masked implementations, this conclusion does not hold anymore. While a single distinguisher can be used to compare the susceptibility of different unprotected devices to first-order DPA, understanding second-order attacks requires to carefully investigate the information leakages and the adversaries exploiting these leakages, separately. Using a framework put forward by Standaert et al. at Eurocrypt 2009, we provide the first analysis that explores these two topics in the case of a masked implementation exhibiting a Hamming weight leakage model. Our results lead to refined intuitions regarding the efficiency of various practically-relevant distinguishers. Further, we also investigate the case of second-and third-order masking (i.e. using three and four shares to represent one value). This evaluation confirms that higher-order masking only leads to significant security improvements if the secret sharing is combined with a sufficient amount of noise. Eventually, we show that an information theoretic analysis allows determining this necessary noise level, for different masking schemes and target security levels, with high accuracy and smaller data complexity than previous methods.

The market for RFID technology has grown rapidly over the past few years. Going along with the proliferation of RFID technology is an increasing demand for secure and privacy-preserving applications. In this context, RFID tags need to be protected against physical attacks such as Differential Power Analysis (DPA) and fault attacks. The main obstacles towards secure RFID are the extreme constraints of passive tags in terms of power consumption and silicon area, which makes the integration of countermeasures against physical attacks even more difficult than for other types of embedded systems. In this paper we propose a fresh re-keying scheme that is especially suited for challenge-response protocols such as used to authenticate tags. We evaluate the resistance of our scheme against fault and side-channel analysis, and introduce a simple architecture for VLSI implementation on RFID tags. In addition, we estimate the cost of our scheme in terms of area and execution time for various sec... Abstract. The market for RFID technology has grown rapidly over the past few years. Going along with the proliferation of RFID technology is an increasing demand for secure and privacy-preserving applications. In this context, RFID tags need to be protected against physical attacks such as Differential Power Analysis (DPA) and fault attacks. The main obstacles towards secure RFID are the extreme constraints of passive tags in terms of power consumption and silicon area, which makes the integration of countermeasures against physical attacks even more difficult than for other types of embedded systems. In this paper we propose a fresh re-keying scheme that is especially suited for challenge-response protocols such as used to authenticate tags. We evaluate the resistance of our scheme against fault and side-channel analysis, and introduce a simple architecture for VLSI implementation on RFID tags. In addition, we estimate the cost of our scheme in terms of area and execution time for various security/performance trade-offs. Our experimental results show that the proposed re-keying scheme provides better security (and does so at less cost) than other state-of-the-art countermeasures.

Abstract. Together with masking, shuffling is one of the most frequently considered solutions to improve the security of small embedded devices against side-channel attacks. In this paper, we provide a comprehensive study of this countermeasure, including improved implementations and a careful information theoretic and security analysis of its different variants. Our analyses lead to important conclusions as they moderate the strong security improvements claimed in previous works. They suggest that simplified versions of shuffling (e.g. using random start indexes) can be significantly weaker than their counterpart using full permutations. We further show with an experimental case study that such simplified versions can be as easy to attack as unprotected implementations. We finally exhibit the existence of "indirect leakages" in shuffled implementations that can be exploited due to the different leakage models of the different resources used in cryptographic implementations. This suggests the design of fully shuffled (and efficient) implementations, were both the execution order of the instructions and the physical resources used are randomized, as an interesting scope for further research.

Leakage-resilient constructions have attracted significant attention over the last couple of years. In practice, pseudorandom functions are among the most important such primitives, because they are stateless and do not require a secure initialization as, e.g. stream ciphers. However, their deployment in actual applications is still limited by security and efficiency concerns. This paper contributes to solve these issues in two directions. On the one hand, we highlight that the condition of bounded data complexity, that is guaranteed by previous leakage-resilient constructions, may not be enough to obtain practical security. We show experimentally that, if implemented in an 8-bit microcontroller, such constructions can actually be broken. On the other hand, we present tweaks for tree-based leakage-resilient PRFs that improve their efficiency and their security, by taking advantage of parallel implementations. Our security analyses are based on worst-case attacks in a noise-free setting and suggest that under reasonable assumptions, the side-channel resistance of our construction grows super-exponentially with a security parameter that corresponds to the degree of parallelism of the implementation. In addition, it exhibits that standard DPA attacks are not the most relevant tool for evaluating such leakage-resilient constructions and may lead to overestimated security. As a consequence, we investigate more sophisticated tools based on lattice reduction, which turn out to be powerful in the physical cryptanalysis of these primitives. Eventually, we put forward that the AES is not perfectly suited for integration in a leakage-resilient design. This observation raises interesting challenges for developing block ciphers with better properties regarding leakage-resilience.

No abstract