International Association for Cryptologic Research

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2013-05-28
05:21 [Pub][ePrint]

Recent advances in lattice cryptography, mainly stemming from the

development of ring-based primitives such as ring-$\\lwe$, have made it

possible to design cryptographic schemes whose efficiency is

competitive with that of more traditional number-theoretic ones, along

with entirely new applications like fully homomorphic encryption.

Unfortunately, realizing the full potential of ring-based cryptography

has so far been hindered by a lack of practical algorithms and

analytical tools for working in this context. As a result, most

previous works have focused on very special classes of rings such as

power-of-two cyclotomics, which significantly restricts the possible

applications.

We bridge this gap by introducing a toolkit of fast, modular

algorithms and analytical techniques that can be used in a wide

variety of ring-based cryptographic applications, particularly those

built around ring-\\lwe. Our techniques yield applications that work

in \\emph{arbitrary} cyclotomic rings, with \\emph{no loss} in their

underlying worst-case hardness guarantees, and very little loss in

computational efficiency, relative to power-of-two cyclotomics. To

demonstrate the toolkit\'s applicability, we develop two illustrative

applications: a public-key cryptosystem and a somewhat homomorphic\'\'

symmetric encryption scheme. Both apply to arbitrary cyclotomics, have

tight parameters, and very efficient implementations.

05:21 [Pub][ePrint]

Measuring power consumption for side-channel analysis typically uses an oscilloscope, which measures the data relative to an internal timebase. By synchronizing the sampling clock to the clock of the target device, the data storage and sampling requirements are considerably relaxed; the attack will succeed with a much lower sample rate. Previous work has demonstrated this on a system with a fixed and easily available clock; but real devices will often have an inaccessible internal oscillator, and may purposely vary the frequency this oscillator runs at (the Varying Clock countermeasure).

This work measures the performance of a synchronous sampling system attacking a modern microcontroller running a software AES implementation. This attack is characterized under three conditions: with a stable clock, with a clock that randomly varies between 4.5~MHz--12.7~MHz, and with an internal oscillator that randomly varies between 7.41~MHz--7.49~MHz.

Traces captured with the synchronous sampling technique can be processed with a standard Differential Power Analysis (DPA) style attack in all three cases, whereas when an oscilloscope is used only the stable oscillator setup is successful. This work also develops the required hardware to recover the internal clock of a device which does not have an externally available clock.

05:21 [Pub][ePrint]

For security applications in wireless sensor networks (WSNs), choosing best algorithms in terms of energy-efficiency and of small memory requirements is a real challenge because the sensor networks must be autonomous. In \\cite{EisenbarthGGHIKKNPRSO12,LawDH06}, the authors have benchmarked on a dedicated platform some block-ciphers and have deduced the best candidates to use in the context of small embedded platforms.

This article proposes to study on a dedicated platform of sensors most of the recent lightweight block ciphers as well as some conventional block ciphers. First, we describe the design of the chosen block ciphers with a security summary and we then present some implementation tests performed on our platform.

05:21 [Pub][ePrint]

We consider a class of two-party function evaluation protocols in which the parties are allowed to use ideal functionalities as well as a set of powerful primitives, namely commitments, homomorphic encryption, and certain zero-knowledge proofs. We illustrate that with these it is possible to capture protocols for oblivious transfer, coin-flipping, and generation of multiplication-triple.

We show how any protocol in our class can be compiled to a symbolic representation expressed as a process in an abstract process calculus, and prove a general computational soundness theorem implying that if the protocol realises a given ideal functionality in the symbolic setting, then the original version also realises the ideal functionality in the standard computational UC setting. In other words, the theorem allows us to transfer a proof in the abstract symbolic setting to a proof in the standard UC model.

Finally, we show that the symbolic interpretation is simple enough in a number of cases for the symbolic proof to be partly automated using the ProVerif tool.

05:21 [Pub][ePrint]

Lattice-based signature schemes constitute an interesting alternative to RSA and discrete logarithm based systems which may become insecure in the future, for example due to the possibility of quantum attacks. A particularly interesting scheme in this context is the GPV signature scheme [GPV08] combined with the trapdoor construction from Micciancio and Peikert [MP12] as it admits strong security proofs and is believed to be very efficient in practice. This paper confirms this belief and shows how to improve the GPV scheme in terms of space and running time and presents an implementation of the optimized scheme. A ring variant of this scheme is also introduced which leads to a more efficient construction. Experimental results show that GPV with the new trapdoor construction is competitive to the signature schemes that are currently used in practice.

05:21 [Pub][ePrint]

The development of a standardised testing methodology for side-channel resistance of cryptographic devices is an issue that has received recent focus from standardisation bodies such as NIST. Statistical techniques such as hypothesis and significance testing appear to be ideally suited for this purpose. In this work we evaluate the candidacy of three such tests: a \\emph{t}-test proposed by Cryptography Research Inc., and two mutual information-based tests. We compare the detection tests in a theoretical setting by conducting an \\emph{a priori} statistical power analysis, covering previously unforeseen problems arising from multiple hypothesis testing, and analyse the practical application of the tests through a case study using an implementation of the AES on an ARM7 microcontroller, demonstrating a trade-off between test genericity and data and computational complexity.

05:21 [Pub][ePrint]

We describe a quasi-linear algorithm for computing Igusa class polynomials of Jacobians of genus 2 curves via complex floating-point approximations of their roots. After providing an explicit treatment of the computations in quartic CM fields and their Galois closures, we pursue an approach due to Dupont for evaluating ϑ-constants in quasi-linear time using Newton iterations on the Borchardt mean. We report on experiments with our implementation and present an example with class number 17608.

05:21 [Pub][ePrint]

Composite-order bilinear groups provide many structural features that have proved useful for both constructing cryptographic primitives and as a technique in security reductions. Despite these convenient features, however, composite-order bilinear groups are less desirable than prime-order bilinear groups for reasons of efficiency. A recent line of work has therefore focused on translating these structural features from the composite-order to the prime-order setting; much of this work focused on two such features, projecting and canceling, in isolation, but a recent result due to Seo and Cheon showed that both features can be obtained simultaneously in the prime-order setting.

In this paper, we reinterpret the construction of Seo and Cheon in the context of dual pairing vector spaces, a tool previously used to simulate other desirable features of composite-order groups in the prime-order setting. In this way, we are able to obtain a unified framework that simulates all of the known composite-order features in the prime-order setting. We demonstrate the strength of this framework by showing that the addition of even a weak form of projecting on top of the pre-existing uses of dual pairing vector spaces can be leveraged to \"boost\" a fully IND-CPA secure identity-based encryption scheme to one that is fully IND-CCA1 secure.

05:21 [Pub][ePrint]

CLEFIA is a 128-bit block cipher proposed by Sony Corporation in 2007. Our paper introduces a new chosen text attack, impossible differential-linear attack, on iterated cryptosystems. The attack is efficient for full-round CLEFIA without whitening keys. In the paper, we construct a 14-round impossible differential distinguisher. Based on the distinguisher, we present an effective attack on full-round CLEFIA-128 with data complexity of $2^{126.52}$, recovering 91-bit subkeys in total. Besides, the results of 15/16/17-round CLEFIA-128 are given in the Appendix B/C/D. Our attack can also applied to CLEFIA-192 and CLEFIA-256.

05:21 [Pub][ePrint]

Few days ago Grigoriev and Shpilrain have proposed to build a system for transmission of information without a shared secret, or essentially a sort of public key cryptosystem, based on properties of physical systems.

In this paper we show that their second scheme based on capacitors is insecure and extremely easy to break in practice.

05:21 [Pub][ePrint]

In hardware, substitution boxes for block ciphers can be saved already masked in the implementation.

The masks must be chosen under two constraints:

their number is determined by the implementation area and their properties should allow to deny high-order zero-offset attacks of highest degree.

First, we show that this problem translates into a known trade-off in Boolean functions, namely

finding correlation-immune functions of lowest weight.

For instance, this allows to prove that a byte-oriented block cipher such as AES can be protected with only $16$ mask values against zero-offset correlation power attacks of orders $1$, $2$ and $3$.

Second, we study $d$th-order correlation-immune Boolean functions $\\F_2^n \\to \\F_2$ of low-weight

and exhibit such functions of minimal weight found by a satisfiability modulo theory tool.

In particular, we give the minimal weight for $n \\leq 10$.

Some of these results were not known previously, such as the minimal weight for

$(n=9, d=4)$ and

$(n=10, d \\in \\{4,5,6\\})$.

These results set new bounds for the minimal number of lines of binary orthogonal arrays.

In particular, we point out that the minimal weight $w_{n,d}$ of a $d$th-order correlation-immune function might not be increasing with the number of variables $n$.