## CryptoDB

### Vincent Rijmen

#### Publications

Year
Venue
Title
2020
JOFC
Linear cryptanalysis is considered to be one of the strongest techniques in the cryptanalyst’s arsenal. In most cases, Matsui’s Algorithm 2 is used for the key recovery part of the attack. The success rate analysis of this algorithm is based on an assumption regarding the bias of a linear approximation for a wrong key, known as the wrong-key-randomization hypothesis. This hypothesis was refined by Bogdanov and Tischhauser to take into account the stochastic nature of the bias for a wrong key. We provide further refinements to the analysis of Matsui’s Algorithm 2 by considering sampling without replacement. This paper derives the distribution of the observed bias for wrong keys when sampling is done without replacement and shows that less data are required in this scenario. It also develops formulas for the success probability and the required data complexity when this approach is taken. The formulas predict that the success probability may reach a peak and then decrease as more pairs are considered. We provide a new explanation for this behavior and derive the conditions for encountering it. We empirically verify our results and compare them to previous work.
2020
ASIACRYPT
ARX algorithms are a class of symmetric-key algorithms constructed by Addition, Rotation, and XOR, which achieve the best software performances in low-end microcontrollers. To evaluate the resistance of an ARX cipher against differential cryptanalysis and its variants, the recent automated methods employ constraint satisfaction solvers, such as SMT solvers, to search for optimal characteristics. The main difficulty to formulate this search as a constraint satisfaction problem is obtaining the differential models of the non-linear operations, that is, the constraints describing the differential probability of each non-linear operation of the cipher. While an efficient bit-vector differential model was obtained for the modular addition with two variable inputs, no differential model for the modular addition by a constant has been proposed so far, preventing ARX ciphers including this operation from being evaluated with automated methods. In this paper, we present the first bit-vector differential model for the n-bit modular addition by a constant input. Our model contains O(log2(n)) basic bit-vector constraints and describes the binary logarithm of the differential probability. We also represent an SMT-based automated method to look for differential characteristics of ARX, including constant additions, and we provide an open-source tool ArxPy to find ARX differential characteristics in a fully automated way. To provide some examples, we have searched for related-key differential characteristics of TEA, XTEA, HIGHT, and LEA, obtaining better results than previous works. Our differential model and our automated tool allow cipher designers to select the best constant inputs for modular additions and cryptanalysts to evaluate the resistance of ARX ciphers against differential attacks.
2019
TCHES
Cryptographic implementations on embedded systems need to be protected against physical attacks. Today, this means that apart from incorporating countermeasures against side-channel analysis, implementations must also withstand fault attacks and combined attacks. Recent proposals in this area have shown that there is a big tradeoff between the implementation cost and the strength of the adversary model. In this work, we introduce a new combined countermeasure M&amp;M that combines Masking with information-theoretic MAC tags and infective computation. It works in a stronger adversary model than the existing scheme ParTI, yet is a lot less costly to implement than the provably secure MPC-based scheme CAPA. We demonstrate M&amp;M with a SCA- and DFA-secure implementation of the AES block cipher. We evaluate the side-channel leakage of the second-order secure design with a non-specific t-test and use simulation to validate the fault resistance.
2018
TCHES
Glitches entail a great issue when securing a cryptographic implementation in hardware. Several masking schemes have been proposed in the literature that provide security even in the presence of glitches. The key property that allows this protection was introduced in threshold implementations as non-completeness. We address crucial points to ensure the right compliance of this property especially for low-latency implementations. Specifically, we first discuss the existence of a flaw in DSD 2017 implementation of Keccak by Gross et al. in violation of the non-completeness property and propose a solution. We perform a side-channel evaluation on the first-order and second-order implementations of the proposed design where no leakage is detected with up to 55 million traces. Then, we present a method to ensure a non-complete scheme of an unrolled implementation applicable to any order of security or algebraic degree of the shared function. By using this method we design a two-rounds unrolled first-order Keccak-
2016
EUROCRYPT
2016
CRYPTO
2016
CHES
2015
JOFC
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
FSE
2015
CRYPTO
2015
EUROCRYPT
2014
EPRINT
2014
EPRINT
2014
ASIACRYPT
2014
FSE
2013
ASIACRYPT
2013
FSE
2012
CHES
2012
ASIACRYPT
2011
JOFC
2010
EPRINT
We introduce the rebound attack as a variant of differential cryptanalysis on hash functions and apply it to the hash function Whirlpool, standardized by ISO/IEC. We give attacks on reduced variants of the Whirlpool hash function and the Whirlpool compression function. Next, we introduce the subspace problems as generalizations of near-collision resistance. Finally, we present distinguishers based on the rebound attack, that apply to the full compression function of Whirlpool and the underlying block cipher $W$.
2010
EPRINT
A new attack on AES-128.
2010
FSE
2009
ASIACRYPT
2008
EPRINT
This is the first article analyzing the security of SHA-256 against fast collision search which considers the recent attacks by Wang et al. We show the limits of applying techniques known so far to SHA-256. Next we introduce a new type of perturbation vector which circumvents the identified limits. This new technique is then applied to the unmodified SHA-256. Exploiting the combination of Boolean functions and modular addition together with the newly developed technique allows us to derive collision-producing characteristics for step-reduced SHA-256, which was not possible before. Although our results do not threaten the security of SHA-256, we show that the low probability of a single local collision may give rise to a false sense of security.
2007
ASIACRYPT
2007
ASIACRYPT
2006
FSE
2006
FSE
2006
EPRINT
In this paper we study the probability of differentials and characteristics over 2 rounds of the AES with the objective to understand how the components of the AES round transformation interact. We extend and correct the analysis of the differential properties of the multiplicative inverse in GF($2^n$). We show that AES has characteristics with a fixed-key probability that is many times larger than the EDP. For instance, in the case of 2-round AES, we measured factors up to $2^{100}$. We study the number of characteristics with EDP $>0$ whose probability adds up to the probability of a differential and derive formulas that allow to produce a close estimate of this number for any differential. We show how the properties discovered in our study can be used to explain the values of the differentials with the largest EDP values and to construct new distinguishers using truncated differentials.
2006
EPRINT
In this article, we present a second preimage attack on a double block-length hash proposal presented at FSE 2006. If the hash function is instantiated with DESX as underlying block cipher, we are able to construct second preimages deterministically. Nevertheless, this second preimage attack does not render the hash scheme insecure. For the hash scheme, we only show that it should not be instantiated with DESX but AES should rather be used. However, we use the instantiation of this hash scheme with DESX to introduce a new property of iterated hash functions, namely a so-called b-block bypass. We will show that if an iterated hash function possesses a b-block bypass, then this implies that second preimages can be constructed. Additionally, the attacker has more degrees of freedom for constructing the second preimage.
2006
EPRINT
MAC algorithms can provide cryptographically secure authentication services. One of the most popular algorithms in commercial applications is HMAC based on the hash functions MD5 or SHA-1. In the light of new collision search methods for members of the MD4 family including SHA-1, the security of HMAC based on these hash functions is reconsidered. We present a new method to recover both the inner- and the outer key used in HMAC when instantiated with a concrete hash function by observing text/MAC pairs. In addition to collisions, also other non-random properties of the hash function are used in this new attack. Among the examples of the proposed method, the first theoretical full key recovery attack on NMAC-MD5 is presented. Other examples are distinguishing, forgery and partial or full key recovery attacks on NMAC/HMAC-SHA-1 with a reduced number of steps (up to 61 out of 80). This information about the new, reduced security margin serves as an input to the selection of algorithms for authentication purposes.
2005
FSE
2005
FSE
2005
EPRINT
We report on the experiments we performed in order to assess the security of SHA-1 against the attack by Chabaud and Joux. We present some ideas for optimizations of the attack and some properties of the message expansion routine. Finally, we show that for a reduced version of SHA-1, with 53 rounds instead of 80, it is possible to find collisions in less than $2^{80}$ operations.
2005
EPRINT
We present a collision attack on the recently proposed hash function SMASH. The attack uses negligible resources and we conjecture that it works for all hash functions built following the design method of SMASH.
2005
EPRINT
At FSE 2005 we presented a new MAC Construction called Alred and a Specific Instance Alpha-MAC. In the presentation we announced a variant of Alpha-MAC under the (working) name Beta-MAC, that can be seen as an optimized version of Alpha-MAC. We have renamed Beta-MAC to Pelican and present its design in this paper. Pelican is based on Rijndael and a factor 2.5 more efficient than CBC-MAC with Rijndael, while providing a comparable claimed security level.
2005
EPRINT
In this paper, we derive the probability distributions of difference propagation probabilities and input-output correlations for random functions and block ciphers, for several of them for the first time. We show that these parameters have distributions that are well-studied in the field of probability such as the normal, Poisson, Gamma and extreme value distributions. For Markov ciphers there exists a solid theory that expresses bounds on the complexity of differential and linear cryptanalysis in terms of average difference propagation probabilities and average correlations, where the average is taken over the keys. The propagation probabilities and correlations exploited in differential and linear cryptanalysis actually depend on the key and hence so does the attack complexity. The theory of Markov ciphers does not make statements on the distributions of these fixed-key properties but rather makes the assumption that their values will be close to the average for the vast majority of keys. This assumption is made explicit in the form of the hypothesis of stochastic equivalence. In this paper, we study the distributions of propagation properties that are relevant in the resistance of {\em key-alternating ciphers} against differential and linear cryptanalysis. Key-alternating ciphers are basically iterative ciphers where round keys are applied by an XOR operation in between unkeyed rounds and are a sub-class of Markov ciphers. We give the distributions of fixed-key difference propagation probability and fixed-key correlation of iterative ciphers. We show that for key-alternating ciphers, the hypothesis of stochastic equivalence can be discarded. In its place comes the explicit formulation of the distribution of fixed-key \emph{differential probability (DP)} of a differential in terms of its \emph{expected differential probability (EDP)} and the distribution of the fixed-key \emph{linear probability} (or rather \emph{potential}) (\emph{LP}) of a linear approximation (or hull) in terms of its \emph{expected linear probability (ELP)}. Here the ELP and EDP are defined by disregarding the key schedule of the block cipher and taking the average over independently selected round keys, instead of over all cipher keys. Proving these distributions requires no assumptions standardly made in Markov cipher theory as perfectly uniform behavior, independently acting rounds or the technique of averaging over keys. For key-alternating ciphers, we show that if the EDP is equal to $2^{-n}$ with $n$ the block length, the fixed-key DP has a distribution that is very close to that in a random $n$-bit cipher. The same holds for the ELP and the corresponding fixed-key LP. Finally we present a technique for computing bounds on the EDP based on the distribution of probabilities of differential characteristics and of the ELP based on the distribution of LP of linear characteristics.
2002
EUROCRYPT
2001
FSE
2001
FSE
2001
FSE
1999
ASIACRYPT
1999
FSE
1999
FSE
1998
ASIACRYPT
1998
FSE
1998
FSE
1997
EUROCRYPT
1997
FSE
1997
FSE
1996
FSE
1994
FSE
1994
FSE
1993
CRYPTO

Eurocrypt 2019
Eurocrypt 2018
FSE 2015
Asiacrypt 2013
FSE 2013
Eurocrypt 2012
FSE 2012
Crypto 2011
Eurocrypt 2011
Asiacrypt 2010
Asiacrypt 2009
FSE 2008
Asiacrypt 2008
Asiacrypt 2005
Eurocrypt 2004
Asiacrypt 2004
Asiacrypt 2003
CHES 2003
FSE 2003
FSE 2002
Eurocrypt 2001
Asiacrypt 2001