International Association for Cryptologic Research

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2014-08-05
21:17 [Pub][ePrint]

In this paper we revisit the notion of generalized universal composability (GUC)

introduced by Canetti, Dodis, Pass and Walfish in 2007. The GUC model was

intended to model a practical setting where setup parameters, like a PKI or a CRS,

are made public once and for all and then used by many different protocols.

We show that there exist protocols which can be proven secure in the GUC model,

but which are obviously insecure in practice, in the setting that the GUC model was

intended to capture. We then proceed to revise the GUC model to a version that

better models the intended practical setting. We call the new notion strong generalized

UC. We finally prove that the GUC protocols proposed by Canetti, Dodis, Pass and Walfish

are also strong GUC secure, i.e., whereas there is a problem with the model, the

protocols seem to be secure in the intended setting.

21:17 [Pub][ePrint]

In the last few years garbled circuits (GC) have been elevated from being merely a component in Yao\'s protocol for secure two-party computation, to a cryptographic primitive in its own right, following the growing number applications that use GCs.

Zero-Knowledge (ZK) protocols is one of these examples: In a recent paper Jawurek et al. [JKO13] showed that GCs can be used to construct efficient ZK for unstructured languages. In this work we show that due to the property of this particular scenario (i.e., one of the party knows all the secret input bits, and therefore all intermediate values in the computation), we can construct more efficient garbled schemes specifically tailored to this goal.

As a highlight of our result, in one of our constructions only one encryption per gate needs to be communicated, and XOR gates never require any cryptographic operation.

In addition to making a step forward towards more practical ZK, we believe that our contribution is also interesting from a conceptual point of view: in the terminology of Bellare et al. [BHR12] our garbling schemes achieve authenticity, but no privacy nor obliviousness, therefore representing the first natural separation between those notions.

21:17 [Pub][ePrint]

Lattice-based cryptographic primitives are believed to offer resilience against attacks by quantum computers. We demonstrate the practicality of post-quantum key exchange by constructing ciphersuites for the Transport Layer Security (TLS) protocol that provide key exchange based on the ring learning with errors (R-LWE) problem; we accompany these ciphersuites with a rigorous proof of security. Our approach ties lattice-based key exchange together with traditional authentication using RSA or elliptic curve digital signatures: the post-quantum key exchange provides forward secrecy against future quantum attackers, while authentication can be provided using RSA keys that are issued by today\'s commercial certificate authorities, smoothing the path to adoption.

Our cryptographically secure implementation, aimed at the 128-bit security level, reveals that the performance price when switching from non-quantum-safe key exchange is not too high. With our R-LWE ciphersuites integrated into the OpenSSL library and using the Apache web server on a 2-core desktop computer, we could serve 506 RLWE-ECDSA-AES128-GCM-SHA256 HTTPS connections per second for a 10 KiB payload. Compared to elliptic curve Diffie--Hellman, this means an 8 KiB increased handshake size and a reduction in throughput of only 21%. This demonstrates that post-quantum key-exchange can already be considered practical.

2014-08-04
21:40 [Job][New]

A 4 year PhD student position is available at the Department of Informatics of the University of Bergen. Some of the possible research directions are coding theory, cryptography, Boolean functions, sequence design.

Information on application requirements and work conditions can be found at http://www.jobbnorge.no/ledige-stillinger/stilling/103925/stipendiat-i-informatikk

00:17 [Pub][ePrint]

A machine is said to be {\\em oblivious} if the sequences of memory accesses made by the machine for two inputs with the same running time are identically (or close to identically) distributed. Oblivious RAM (ORAM) compilers -- compilers that turn any RAM program $\\Pi$ into an oblivious RAM $\\Pi\'$, while incurring only a \"small\", polylogarithmic, slow-down -- have been extensively studied since the work of Goldreich and Ostrovsky (JACM 1996), and have numerous fundamental applications. These compilers, however, do not leverage parallelism: even if $\\Pi$ can be heavily parallelized, $\\Pi\'$ will be inherently sequential.

In this work, we present the first {\\em Oblivious Parallel RAM (OPRAM)} compiler, which compiles any PRAM into an oblivious PRAM while incurring only a polylogarithmic slowdown.

2014-08-03
13:39 [Job][Update]

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You can be part of an ambitious team of professionals operating in an incredibly exciting industry to help the world be more connected and more secure.

We are looking for passionate, talented experts in the field of Crypto & Security. Examplary roles include:

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• Currently we are hiring in San Jose (US), Eindhoven (NL), Glasgow (UK), Gratkorn (AT), Hamburg (DE) and Leuven (BE). There are more than 30 Crypto & Security positions for all sort of experience levels!

We are looking forward to your application via our Crypto & Security career website on LinkedIn.

2014-07-31
21:42 [Event][New]

Submission: 6 October 2014
From March 23 to March 25
Location: Warsaw, Poland

21:17 [Pub][ePrint]

This paper presents new speed records for multiprecision multiplication on the AVR ATmega family of 8-bit microcontrollers. For example, our software takes only 1976 cycles for the multiplication of two 160-bit integers; this is more than 15% faster than previous work. For 256-bit inputs, our software is not only the first to break through the 6000-cycle barrier; with only 4797 cycles it also breaks through the 5000-cycle barrier and is more than 21% faster than previous work.We achieve these speed records by carefully optimizing the Karatsuba multiplication technique for AVR ATmega. One might expect that subquadratic-complexity Karatsuba multiplication is only faster than algorithms with quadratic complexity for large inputs. This paper shows that it is in fact faster than fully unrolled product-scanning multiplication already for surprisingly small inputs, starting at 48 bits. Our results thus make Karatsuba multiplication the method of choice for high-performance implementations of elliptic-curve cryptography on AVR ATmega microcontrollers.

21:17 [Pub][ePrint]

The paper is about algorithms for the inhomogeneous short integer solution problem: Given A, b to find a short vector s such that As \\equiv b (mod q). We consider algorithms for this problem due to Camion and Patarin; Wagner; Schroeppel and Shamir; Howgrave-Graham and Joux; Becker, Coron and Joux. Our main results include: Applying the Hermite normal form (HNF) to get faster algorithms; A heuristic analysis of the HGJ and BCJ algorithms in the case of density greater than one; An improved cryptanalysis of the SWIFFT hash function.

12:17 [Pub][ePrint]

Structure-preserving signature schemes can be very useful in the construction of new cryptographic operations like blind signatures. Recently several of these schemes have been proposed. The security of signature-preserving signature schemes is still proved by hand, which can be a laborious task. One of the ways to prove security of these schemes algebraic analysis can be used. We present an approach to perform this analysis and the first tool, CheckSPS, that can do an algebraic security analysis of these schemes, using SMT solvers as backend. This can help in constructing new schemes and analyse existing schemes. Our tool can handle all the common security objectives for signature schemes, i.e. existential unforgeability and strong existential unforgeability, and all the common capabilities for adversaries, i.e. random message attacks, non-adaptive chosen message attacks and adaptive chosen message attacks. The tool is sound, so if an attack is found it is actually possible to construct a forged signature.

12:17 [Pub][ePrint]

Discrete Gaussian sampling is an integral part of many lattice

based cryptosystems such as public-key encryption, digital signature schemes and homomorphic encryption schemes. In this paper we propose a compact and fast Knuth-Yao sampler for sampling from a narrow discrete Gaussian distribution with very high precision. The designed samplers have a maximum statistical distance of $2^{-90}$ to a true discrete Gaussian distribution. In this paper we investigate various optimization techniques to achieve minimum area and cycle requirement. For the standard deviation 3.33, the most area-optimal implementation of the bit-scan operation based Knuth-Yao sampler consumes 30 slices on the Xilinx Virtex 5 FPGAs, and requires on average 17 cycles to generate a sample. We improve the speed of the sampler by using a precomputed table that directly maps the initial random bits into samples with very high probability. The fast sampler consumes 35 slices and spends on average 2.5 cycles to generate a sample. However the sampler architectures are not secure against timing and power analysis based attacks. In this paper we propose a random shuffle method to protect the Gaussian distributed polynomial against such attacks. The side channel attack resistant sampler architecture consumes 52 slices and spends on average 420 cycles to

generate a polynomial of 256 coefficients.