Diseño de circuitos integrados y seguridad de circuitos criptográficos frente a ataques

Muchos sistemas electrónicos incorporan dispositivos criptográficos que implementan algoritmos que cifran la información almacenada. Pero aun cuando los algoritmos sean muy seguros, estos dispositivos pueden llegar a revelar cierta información debido a su implementación física, mediante el empleo de los llamados ataques laterales. Estos ataques hacen uso de información obtenida durante del funcionamiento del circuito para obtener información sobre la clave utilizada. Por lo tanto, hay que cuidar la implementación física de los dispositivos criptográficos, para minimizar la posibilidad de pérdida de información mediante estos ataques. En nuestras líneas de investigación estamos trabajando en analizar la vulnerabilidad de implementaciones de circuitos criptográficos, fundamentalmente cifradores de clave privada, frente a ataques laterales pasivos y activos. Estos ataques obtienen información de la clave almacenada mediante la medida de magnitudes físicas como el consumo de potencia o la radiación electromagnética durante el funcionamiento del circuito o alterando las condiciones de funcionamiento para introducirles fallos y comparar las salidas sin y con fallos. En esta comunicación presentamos un breve resumen del estado del arte en los ataques laterales sobre implementaciones hardware de cifradores, algunos de los temas en los que estamos trabajando y algunos resultados obtenidos por nuestro grupo de investigación.Many electronic systems include devices that implement cryptographic algorithms that encrypt stored information. But even if the algorithms are very safe, these devices can reveal some information because of its physical implementation, through the use of so-called side channel attacks. These attacks make use of information obtained during the operation of the circuit to obtain information of the used key. Therefore, we must take care of the physical implementation of cryptographic devices to minimize the possibility of loss of information through these types of attacks. In our research we are working on analyzing the vulnerability of implementations of cryptographic circuits, mainly private key ciphers, against side channel attacks, passive and active. These attacks obtain key information stored by measuring physical quantities such as power consumption or electromagnetic radiation during operation of the circuit, or altering the operating conditions to introduce faults and compare the output with and without faults. In this paper we present a brief summary of the state of art of side channel attacks on ciphers hardware implementations, some of the topics we are working and some results obtained by our research group.Junta de Andalucía CRIPTO-BIO (Diseño Microelectrónico para Autenticación Cripto-Biométrica)Ministerio de Ciencia y Tecnología (España) P08-TIC3674, CITIES (Circuitos Integrados para transmisión de información especialmente segura)Ministerio de Economía y Competitividad (España) TEC2010-16870 y CESAR (Circuitos microelectrónicos seguros frente a ataques laterales) y TEC2013-45523-

Multiple Bytes Differential Fault Analysis on CLEFIA

This paper examines the strength of CLEFIA against multiple bytes differential fault attack. Firstly, it presents the principle of CLEFIA algorithm and differential fault analysis; then, according to injecting faults into the rth,r-1th,r-2th CLEFIA round three conditions, proposes three fault models and corresponding analysis methods; finally, all of the fault model and analysis methods above have been verified through software simulation. Experiment results demonstrate that: CLEFIA is vulnerable to differential fault attack due to its Feistel structure and S-box feature, 5-6,6-8,2 faults are needed to recover CLEFIA-128 based on the three fault models in this paper respectively, multiple byte faults model can greatly improve the attack practicality and even the attack efficiency, and the fault analysis methods in this paper can provide some fault analysis ideas on other block ciphers using S-box

Floating Fault analysis of Trivium under Weaker Assumptions

Trivium is a hardware-oriented stream cipher, and one of the finally chosen ciphers by eSTREAM project. Michal Hojsik and Bohuslav Rudolf presented an effective attack to Trivium, named floating fault analysis, at INDOCRYPT 2008. Their attack makes use of the fault injection and the fault float. In this paper, we present an improvement of this attack. Our attack is under following weaker and more practical assumptions.The fault injection can be made for the state at a random time.The positions of the fault bits are from random one of 3 NFSRs, and from a random area within 8 neighboring bits.We present a checking method, by which either the injecting time and fault positions can be determined, or the state differential at a known time can be determined. Each of these two determinations is enough for floating attack. After the determination, the attacker can averagely obtain 67.167 additional linear equations from 82 original quadratic equations, and obtain 66 additional quadratic equations from 66 original cubic equations

An Improved Differential Fault Attack on Camellia

The S-box lookup is one of the most important operations in cipher algorithm design, and also is the most effective part to prevent traditional linear and differential attacks, however, when the physical implementation of the algorithm is considered, it becomes the weakest part of cryptosystems. This paper studies an active fault based implementation attack on block ciphers with S-box. Firstly, it proposes the basic DFA model and then presents two DFA models for Feistel and SPN structure block ciphers. Secondly, based on the Feistel DFA model, it presents several improved attacks on Camellia encryption and proposes new attacks on Camellia key schedule. By injecting one byte random fault into the r-1th round left register or the the r-1th round key, after solving 8 equations to recover 5 or 6 propagated differential fault of the rth round left register, 5 or 6 bytes of the rth equivalent subkey can be recovered at one time. Simulation experiments demonstrate that about 16 faulty ciphertexts are enough to obtain Camellia-128 key, and about 32, 24 ciphertexts are required to obtain both Camellia-192/256 key with and without FL/FL-1 layer respectively. Compared with the previous study by ZHOU Yongbin et. al. by injecting one byte fault into the rth round left register to recover 1 equivalent subkey byte and obtaining Camellia-128 and Camellia-192/256 with 64 and 96 faulty ciphertexts respectively, our attacks not only extend the fault location, but also improve the fault injection efficiency and decrease the faulty ciphertexts number, besides, our DFA model on Camellia encryption can be easily extended to DFA on Camellia key schedule case, while ZHOU’s can not. The attack model proposed in this paper can be adapted into most of the block ciphers with S-boxes. Finally, the contradictions between traditional cryptography and implementation attacks are analyzed, the state of the art and future directions of the DFA on Block ciphers with S-boxes are discussed

Impossible Fault Analysis of RC4 and Differential Fault Analysis of RC4

Abstract. In this paper we introduce the notion of impossible fault analysis, and present an impossible fault analysis of RC4, whose complexity 2 21 is smaller than the previously best known attack of Hoch and Shamir (2 26), along with an even faster fault analysis of RC4, based on different ideas, with complexity smaller than 2 16.

ANALYSIS OF CRYPTOGRAPHIC ALGORITHMS AGAINST THEORETICAL AND IMPLEMENTATION ATTACKS

This thesis deals with theoretical and implementation analysis of cryptographic functions. Theoretical attacks exploit weaknesses in the mathematical structure of the cryptographic primitive, while implementation attacks leverage on information obtained by its physical implementation, such as leakage through physically observable parameters (side-channel analysis) or susceptibility to errors (fault analysis). In the area of theoretical cryptanalysis, we analyze the resistance of the Keccak-f permutations to differential cryptanalysis (DC). Keccak-f is used in different cryptographic primitives: Keccak (which defines the NIST standard SHA-3), Ketje and Keyak (which are currently at the third round of the CAESAR competition) and the authenticated encryption function Kravatte. In its basic version, DC makes use of differential trails, i.e. sequences of differences through the rounds of the primitive. The power of trails in attacks can be characterized by their weight. The existence of low-weight trails over all but a few rounds would imply a low resistance with respect to DC. We thus present new techniques to effciently generate all 6-round differential trails in Keccak-f up to a given weight, in order to improve known lower bounds. The limit weight we can reach with these new techniques is very high compared to previous attempts in literature for weakly aligned primitives. This allows us to improve the lower bound on 6 rounds from 74 to 92 for the four largest variants of Keccak-f. This result has been used by the authors of Kravatte to choose the number of rounds in their function. Thanks to their abstraction level, some of our techniques are actually more widely applicable than to Keccak-f. So, we formalize them in a generic way. The presented techniques have been integrated in the KeccakTools and are publicly available. In the area of fault analysis, we present several results on differential fault analysis (DFA) on the block cipher AES. Most DFA attacks exploit faults that modify the intermediate state or round key. Very few examples have been presented, that leverage changes in the sequence of operations by reducing the number of rounds. In this direction, we present four DFA attacks that exploit faults that alter the sequence of operations during the final round. In particular, we show how DFA can be conducted when the main operations that compose the AES round function are corrupted, skipped or repeated during the final round. Another aspect of DFA we analyze is the role of the fault model in attacks. We study it from an information theoretical point of view, showing that the knowledge that the attacker has on the injected fault is fundamental to mount a successful attack. In order to soften the a-priori knowledge on the injection technique needed by the attacker, we present a new approach for DFA based on clustering, called J-DFA. The experimental results show that J-DFA allows to successfully recover the key both in classical DFA scenario and when the model does not perfectly match the faults effect. A peculiar result of this method is that, besides the preferred candidate for the key, it also provides the preferred models for the fault. This is a quite remarkable ability because it furnishes precious information which can be used to analyze, compare and characterize different specific injection techniques on different devices. In the area of side-channel attacks, we improve and extend existing attacks against the RSA algorithm, known as partial key exposure attacks. These attacks on RSA show how it is possible to find the factorization of the modulus from the knowledge of some bits of the private key. We present new partial key exposure attacks when the countermeasure known as exponent blinding is used. We first improve known results for common RSA setting by reducing the number of bits or by simplifying the mathematical analysis. Then we present novel attacks for RSA implemented using the Chinese Remainder Theorem, a scenario that has never been analyzed before in this context