International Association for Cryptologic Research

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2013-09-05
06:04 [Job][New]

As part of our participation in the just starting EU FP7 project PRIPARE on privacy engineering and privacy by design, we have an open PhD position in this area.

Evaluation of applications is continuing until the position is filled.

06:04 [Job][New]

I am looking for a PhD student to join the DemTech research project (www.demtech.dk). DemTech\\\'s broad mission is about the role of technology in democratic processes. We work on topics ranging from software engineering and requirements engineering, information security, and program verification, cryptography, in particular ever lasting privacy, but also logic methods, concurrency, and computational social choice. The successful candidate will join an international group consisting of faculty, post-docs, and PhD students. DemTech is working with many governmental institutions around the world. The position runs for three or four years. The application deadline is

13th October 2013, at 23:59 CET

2013-09-04
15:17 [Pub][ePrint]

This paper presents early results of a (very) experimental implementation of the elliptic curve and stream cipher calculations of the Networking and Cryptography library (NaCl), on the TRS-80 Model I. Needless to say, the demonstration that such a library, which has been optimized for many modern platforms including leading edge desktops, servers and, recently, modern microcontrollers, is even feasible on such early home microcomputers is, at best, to be considered a recreation rather than as a practical application of technology. In the process, however, lessons were learned in implementing trade-offs for basic cryptographic primitives and, more importantly maybe, in experimenting with some transformative aspects of retrocomputing.

15:17 [Pub][ePrint]

Counting the number of active S-boxes is a common way to evaluate the security of symmetric key cryptographic schemes against differential attack. Based on Mixed Integer Linear Programming (MILP), Mouha et al proposed a method to accomplish this task automatically for word-oriented symmetric-key ciphers with SPN structures. However, this method can not be applied directly to block ciphers of SPN structures with bitwise permutation diffusion layers (S-bP structures), due to its ignorance of the diffusion effect derived collaboratively by nonlinear substitution layers and bitwise permutation layers. Moreover, the MILP constrains presented in Mouha et al\'s method are not enough to describe the differential propagation behaviour of a linear diffusion layer constructed from a non-MDS code, even an almost MDS code. In this paper we extend Mouha et al\'s method for S-bP structures by introducing new representations for exclusive-or (XOR) differences to describe bit/word level differences simultaneously and by taking the collaborative diffusion effect of S-boxes and bitwise permutations into account. Our method is applied to the block cipher PRESENT-80, an international standard for lightweight symmetric key cryptography, to automatically evaluate its security against differential attacks. We obtain lower bounds on the numbers of active S-boxes in the single-key model for full 31-round PRESENT-80 and in related-key model for round-reduced PRESENT-80 up to 12 rounds, and therefore automatically prove that the full-round PRESENT-80 is secure against single-key differential attack, and the cost of related-key differential attack on the full-round PRESENT-80 is close to that of an exhaustive search: the best related-key differential characteristic for full PRESENT-80 is upper bounded by $2^{-72}$.

15:17 [Pub][ePrint]

We give an algorithm for decomposing given element of Jacobian gruop

into the sum of the decomposed factor, which consists of certain subset of the points of curve.

15:17 [Pub][ePrint]

Faug\\\'ere et al. shows that the decomposition problem of an element of elliptic curve over binary field $F_{2^n}$ reduces to solving low degree equations system over $bF_2$ coming from Weil descent. Using this method, the discrete logarithm problem of elliptic curve over $F_{2^n}$ reduces to linear constrains, i.e., solving equations system using linear algebra of monomial modulo field equations, and its complexity is expected to be subexponential of input size $n$. However, it is pity that at least using linear constrains, it is exponential.

Petit et al. shows that assuming first fall degree assumption and using Gr\\\"obner basis computation, its complexity is heuristically subexponential.

On the other hands, the author shows that the decomposition problem of Jacobian of plane curve over $F_{p^n}$ also essentially reduces to solving low degree equations system over $F_p$ coming from Weil descent.

In this paper, we generalize ($p>2$ cases, Jacobian cases) and revise (precise estimation of first fall degree) the results of Petit et al. and show that the discrete logarithm problem

of elliptic curve over small characteristic field $F_{p^n}$ is subexponential of input size $n$, and the discrete logarithm problem of Jacobian of small genus curve over small characteristic field $F_{p^n}$ is also subexponential of input size $n$,

under first fall degree assumption.

15:17 [Pub][ePrint]

At Eurocrypt 2013, Joye and Libert proposed a method for constructing public key cryptosystems (PKCs) and lossy trapdoor functions (LTDFs) from $(2^\\alpha)^{th}$-power residue symbols. Their work can be viewed as non-trivial extensions of the well-known PKC scheme due to Goldwasser and Micali, and the LTDF scheme due to Freeman et al., respectively. In this paper, we will demonstrate that this kind of work can be extended \\emph{more generally}: all related constructions can work for any $k^{th}$ residues if $k$ only contains small prime factors, instead of $(2^\\alpha)^{th}$-power residues only. The resultant PKCs and LTDFs are more efficient than that from Joye-Libert method in terms of decryption speed with the same message length.

15:17 [Pub][ePrint]

This document describes the symmetric encryption algorithm called Puzzle. It is free and open. The objective of this paper is to get an opinion about its security from the cryptology community. It is separated in two parts, a technical description of the algorithm and its cryptanalysis. The algorithm has some interesting properties :

The block size is variable and unknown from an attacker. The size of the key has no limit and is unknown from an attacker. The key size does not affect the algorithm speed (using a 256 bit key is the same as using a 1024 bit key). The algorithm is much faster than the average cryptographic function. Experimental test showed 600 Mo/s - 4 cycles/byte on an Intel Core 2 Duo P8600 2.40GHz and 1,2 Go/s - 2 cycles/byte on an Intel i5-3210M 2.50GHz. Both CPU had only 2 cores.

15:17 [Pub][ePrint]

Protocols for secure computation enable parties to compute a joint function on their private inputs without revealing anything but the result. A foundation for secure computation is oblivious transfer (OT), which traditionally requires expensive public key cryptography. A more efficient way to perform many OTs is to extend a small number of base OTs using OT extensions based on symmetric cryptography.

In this work we present optimizations and efficient implementations of OT and OT extensions in the semi-honest model. We propose a novel OT protocol with security in the standard model and improve OT extensions with respect to communication complexity, computation complexity, and scalability. We also provide specific optimizations of OT extensions that are tailored to the secure computation protocols of Yao and Goldreich-Micali-Wigderson and reduce the communication complexity even further. We experimentally verify the efficiency gains of our protocols and optimizations. By applying our implementation to current secure computation frameworks, we can securely compute a Levenshtein distance circuit with 1.29 billion AND gates at a rate of 1.2 million AND gates per second. Moreover, we demonstrate the importance of correctly implementing OT within secure computation protocols by presenting an attack on the FastGC framework.

15:17 [Pub][ePrint]

All known protocols implementing broadcast from synchronous point-to-point channels tolerating any $t < n$ Byzantine corruptions have communication complexity at least $\\Omega(\\ell n^2)$. We give cryptographically secure and information-theoretically secure protocols for $t < n$ that communicate $O(\\ell n)$ bits in order to broadcast sufficiently long $\\ell$ bit messages. This matches the optimal communication complexity bound for any protocol allowing to broadcast $\\ell$ bit messages. While broadcast protocols with the optimal communication complexity exist in cases where $t < n/3$ (by Liang and Vaidya in PODC \'11) or $t < n/2$ (by Fitzi and Hirt in PODC \'06), this paper is the first to present such protocols for $t < n$.

15:17 [Pub][ePrint]

In his keynote speech at CHES 2004, Kocher advocated that side-channel attacks were an illustration that formal cryptography was not as secure as it was believed because some assumptions (e.g., no auxiliary information is available during the computation) were not modeled.

This failure is due to the fact that formal methods work with models rather than implementations.

Of course, we can use formal methods to prove non-functional security properties such as the absence of side-channel leakages.

But a common obstacle is that those properties are very low-level and appear incompatible with formalization.

To avoid the discrepancy between the model and the implementation, we apply formal methods directly on the implementation.

Doing so, we can formally prove that an assembly code is leak-free, provided that the hardware it runs on satisfies a finite (and limited) set of properties that we show are realistic.

We apply this technique to prove that a PRESENT implementation in 8~bit AVR assembly code is leak-free.
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