Unprotected Implementation Research Articles

A New Second-Order Side Channel Attack Based on Linear Regression

Since the preliminary works of Kocher et al. in the nineties, studying and enforcing the resistance of cryptographic implementations against side channel analysis (SCA) is became a dynamic and prolific area of embedded security. Stochastic attacks, introduced by Schindler et al., form one of the main families of SCA and they offer a valuable alternative to template attacks which are known to be among the most efficient ones. However, stochastic attacks, as long as template attacks, have been initially designed for adversaries with a perfect copy of the target device in hand. Such a prerequisite makes them a pertinent tool when studying the implementations resistance against the most powerful adversaries, but it limits their pertinence as a cryptanalytic technique. Indeed, getting open access to a copy of the device under attack is difficult in practice and, even when possible, it remains difficult to exploit templates acquired on one device to attack another one. In light of this observation, several papers have been published to adapt stochastic attacks for contexts where the above prerequisite is no longer needed. They succeeded in defining practical attacks against unprotected implementations but no work was published until now to explain how stochastic attacks can be applied against secure implementations. In this paper, we deal with this issue. We first extend the previous analyses of stochastic attacks to highlight their core foundations. Then, we explain how they can be generalized to defeat first-order masking techniques, which are the main SCA countermeasures. Eventually, we illustrate the interest of the new attack by a series of experiments on simulated and real curves.

Leakage Mapping

We propose a generalized framework to evaluate the side-channel information leakage of symmetric block ciphers. The leakage mapping methodology enables the systematic and efficient identification and mitigation of problematic information leakages by exhaustively considering relevant leakage models. The evaluation procedure bounds the anticipated resistance of an implementation to the general class of univariate differential side-channel analysis techniques. Typical applications are demonstrated using the well-known Hamming weight and Hamming distance leakage models, with recommendations for the incorporation of more accurate models. The evaluation results are empirically validated against correlation-based differential side-channel analysis attacks on two typical unprotected implementations of the Advanced Encryption Standard.

Side channel analysis attacks using AM demodulation on commercial smart cards with SEED

We investigate statistical side channel analysis attacks on the SEED block cipher implemented in two commercial smart cards used in a real-world electronic payment system. The first one is a contact-only card and the second one is a combination card. Both cards have no masking scheme at algorithm level and the combination card supports only hiding techniques in hardware level. Our results show that an unprotected implementation of SEED allows one to recover the secret key with low number of power or electromagnetic traces. Moreover, this paper clearly confirms that, although hiding countermeasures such as random current and random noise may increase the number of power traces needed for a successful attack, it is difficult to provide sufficient resistance to side channel attacks for itself. We believe that our results in this research will also be beneficial to the analysis and protection of other algorithms and commercial smart cards.

Mutual Information Analysis: a Comprehensive Study

Mutual Information Analysis is a generic side-channel distinguisher that has been introduced at CHES 2008. It aims to allow successful attacks requiring minimum assumptions and knowledge of the target device by the adversary. In this paper, we compile recent contributions and applications of MIA in a comprehensive study. From a theoretical point of view, we carefully discuss its statistical properties and relationship with probability density estimation tools. From a practical point of view, we apply MIA in two of the most investigated contexts for side-channel attacks. Namely, we consider first-order attacks against an unprotected implementation of the DES in a full custom IC and second-order attacks against a masked implementation of the DES in an 8-bit microcontroller. These experiments allow to put forward the strengths and weaknesses of this new distinguisher and to compare it with standard power analysis attacks using the correlation coefficient.

A FAST AND SECURE ELLIPTIC CURVE SCALAR MULTIPLICATION ALGORITHM OVER GF(pm)

ABSTRACT This paper presents an innovative method for accelerating the elliptic curve scalar multiplication algorithm over GF(pm). The technique uses the substitution of multiplication with squaring and other cheaper operations by exploiting the fact that field squaring is generally less costly than multiplication. Applying this substitution to the traditional formulae, we obtain faster scalar multiplication in unprotected sequential implementations. We also show the significant impact our method has in protecting against simple side channel attacks(SSCA). We modify the ECC scalar multiplication to achieve a faster atomic structure when applying side channel atomicity protection. In contrast to previous atomic operations that assume squarings are indistinguishable from multiplications, our new atomic structure offers true SSCA-protection because it includes squaring in its formulation. In the scalar multiplication using NAF, our atomic blocks speed-up computation up to 30% in contrast to previous atomic implementations.

Differential Side Channel Analysis Attacks on FPGA Implementations of ARIA

In this paper, we first investigate the side channel analysis attack resistance of various FPGA hardware implementations of the ARIA block cipher. The analysis is performed on an FPGA test board dedicated to side channel attacks. Our results show that an unprotected implementation of ARIA allows one to recover the secret key with a low number of power or electromagnetic measurements. We also present a masking countermeasure and analyze its second-order side channel resistance by using various suitable preprocessing functions. Our experimental results clearly confirm that second-order differential side channel analysis attacks also remain a practical threat for masked hardware implementations of ARIA.

Low-cost solutions for preventing simple side-channel analysis: side-channel atomicity

We introduce simple methods to convert a cryptographic algorithm into an algorithm protected against simple side-channel attacks. Contrary to previously known solutions, the proposed techniques are not at the expense of the execution time. Moreover, they are generic and apply to virtually any algorithm. In particular, we present several novel exponentiation algorithms, namely, a protected square-and-multiply algorithm, its right-to-left counterpart, and several protected sliding-window algorithms. We also illustrate our methodology applied to point multiplication on elliptic curves. All these algorithms share the common feature that the complexity is globally unchanged compared to the corresponding unprotected implementations.