International Association for Cryptologic Research

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2012-08-20
00:17 [Pub][JoC]

Abstract  We devise a notion of polynomial runtime suitable for the simulation-based security analysis of multi-party cryptographic protocols. Somewhat surprisingly, straightforward notions of polynomial runtime lack expressivity for reactive tasks and/or lead to an unnatural simulation-based security notion. Indeed, the problem has been recognized in previous works, and several notions of polynomial runtime have already been proposed. However, our new notion, dubbed reactive polynomial time, is the first to combine the following properties: –  it is simple enough to support simple security/runtime analyses, –  it is intuitive in the sense that all intuitively feasible protocols and attacks (and only those) are considered polynomial-time, –  it supports secure composition of protocols in the sense of a universal composition theorem. We work in the Universal Composability (UC) protocol framework. We remark that while the UC framework already features a universal composition theorem, we develop new techniques to prove secure composition in the case of reactively polynomial-time protocols and attacks.

• Content Type Journal Article
• Pages 1-67
• DOI 10.1007/s00145-012-9127-4
• Authors

• Dennis Hofheinz, Karlsruhe Institute of Technology, Karlsruhe, Germany
• Dominique Unruh, University of Tartu, Tartu, Estonia
• Jörn Müller-Quade, Karlsruhe Institute of Technology, Karlsruhe, Germany

• Journal Journal of Cryptology
• Online ISSN 1432-1378
• Print ISSN 0933-2790

From: Thu, 16 Aug 2012 16:03:17 GMT

2012-08-19
17:48 [Conf][Crypto]

CRYPTO 2012 starts today!!

If you have any conference-related stories or photos to share, please email crypto2012@iacr.org.

2012-08-18
06:17 [Pub][ePrint]

Optimizing the maximum, or average, length of the shares in relation to the length of the secret for every given access structure is a difficult and long-standing open problem in cryptology. Most of the known lower bounds on these parameters have been obtained by implicitly or explicitly using that every secret sharing scheme defines a polymatroid related to the access structure. The best bounds that can be obtained by this combinatorial method can be determined by using linear programming, and this can be effectively done for access structures on a small number of participants.

By applying this linear programming approach, we improve some of the known lower bounds for the access structures on five participants and the graph access structures on six participants for which these parameters were still undetermined. Nevertheless, the lower bounds that are obtained by this combinatorial method are not tight in general. For some access structures, they can be improved by adding

to the linear program non-Shannon information inequalities as new constraints. We obtain in this way new separation results for some graph access structures on eight participants and for some ports of non-representable matroids. Finally, we prove that, for two access structures on five participants, the combinatorial lower bound cannot be attained by any linear secret sharing scheme.

06:17 [Pub][ePrint]

RFID-based tag matching allows a reader Rk to determine whether two tags Ti and Tj store

some attributes that jointly fulfill a boolean constraint. The challenge in designing a matching mechanism

is tag privacy. While cheap tags are unable to perform any computation, matching has to be

achieved without revealing the tags\' attributes. In this paper, we present T-MATCH, a protocol for secure

and privacy preserving RFID tag matching. T-MATCH involves a pair of tags Ti and Tj , a reader

Rk, and a backend server S. To ensure tag privacy against Rk and S, T-MATCH employs a new technique

based on secure two-party computation that prevents Rk and S from disclosing tag attributes. For

tag privacy against eavesdroppers, each tag Ti in T-MATCH stores an IND-CPA encryption of its attribute.

Such an encryption allows Rk to update the state of Ti by merely re-encrypting Ti\'s ciphertext.

T-MATCH targets cheap tags that cannot perform any computation, but are only required to store 150

bytes.

06:17 [Pub][ePrint]

We investigate how information leakage reduces computational entropy of a random variable X. Recall that HILL and metric computational entropy are parameterized by quality (how distinguishable is X from a variable Z that has true entropy) and quantity (how much true entropy is there in Z).

We prove an intuitively natural result: conditioning on an event of probability p reduces the quality of metric entropy by a factor of p and the quantity of metric entropy by log 1/p note that this means that the reduction in quantity and quality is the same, because the quantity of entropy is measured on logarithmic scale). Our result improves previous bounds of Dziembowski and Pietrzak (FOCS 2008), where the loss in the \\emph{quantity} of entropy was related to its original quality. The use of metric entropy simplifies the analogous the result of Reingold et. al. (FOCS 2008) for HILL entropy.

Further, we simplify dealing with information leakage by investigating conditional metric entropy. We show that, conditioned on leakage of \\lambda bits, metric entropy gets reduced by a factor 2^\\lambda in quality and \\lambda in quantity.

06:17 [Pub][ePrint]

We get two kinds of new results on nonexistence of generalized bent function. The first one is Based on Feng\'s results by using Schmidt\'s field descent method. For the second kind, considering special property of the field $\\mathbb{Q}(\\zeta_{23^e})$, We get new nonexistence results of generalized bent functions with type $[3,2\\cdot23^e]$.

06:17 [Pub][ePrint]

Functional encryption is an emerging paradigm for public-key encryption that enables fine-grained control of access to encrypted data. In this work, we present new perspectives on security definitions for functional encryption, as well as new lower bounds on what can be achieved. Our main contributions are as follows:

* We show a lower bound for functional encryption that satisfies a weak (non-adaptive) simulation-based security notion, via pseudo-random functions. This is the first lower bound that exploits unbounded collusions in an essential way.

* We put forth and discuss a simulation-based notion of security for functional encryption, with an unbounded simulator (called USIM). We show that this notion interpolates indistinguishability and simulation-based security notions, and has strong correlations to results and barriers in the zero-knowledge and multi-party computation literature.

06:17 [Pub][ePrint]

This paper presents a new security notion, called \\emph{perfect keyword privacy (PKP)}, for non-interactive public-key encryption with keyword search (PEKS) \\cite{bcop04}. Although the conventional security notion for PEKS guarantees that a searchable ciphertext leaks no information about keywords, it gives no guarantee concerning leakage of a keyword from the trapdoor. PKP is a notion for overcoming this fatal deficiency. Since the trapdoor has verification functionality, the popular concept of indistinguishability\'\' is inadequate for capturing the notion of keyword privacy from the trapdoor. Hence, our formalization of PKP depends on the idea of formalizing a perfectly one-way hash function \\cite{can97,cmr98}. We also present \\emph{IND-PKP security} as a useful notion for showing that a given PEKS scheme has PKP. Furthermore, we present PKP+ and IND-PKP+ as enhanced notions of PKP and IND-PKP, respectively. Finally, we present several instances of an IND-PKP or IND-PKP+ secure PEKS scheme, in either the random oracle model or the standard model.

06:17 [Pub][ePrint]

In this paper we present some interesting connections between primitive roots and quadratic non-residues modulo a prime. Using these correlations, we improve the existing randomized algorithm for generating primitive roots and we propose a polynomial deterministic algorithm for generating primitive roots for primes

with special forms (for example, for safe primes). The key point of our improvement is the fact that the evaluation of Legendre-Jacobi symbol is much faster than an exponentiation.

06:17 [Pub][ePrint]

This paper proposes a pseudo random number generator (PRNG) based on quasigroups. The proposed PRNG has low memory requirements, is autonomous and the quality of the output stream of random numbers is better than other available standard PRNG implementations (commercial and open source) in majority of the tests. Comparisons are done using the benchmark NIST Statistical Test Suite and compression tools. Results are presented for quality of raw stream of random numbers and for encryption results using these random numbers.

06:17 [Pub][ePrint]

Several masking schemes to protect cryptographic implementations against side-channel attacks have been proposed. A few considered the glitches, and provided security proofs in presence of such inherent phenomena happening in logic circuits. One which is based on multi-party computation protocols and utilizes Shamir\'s secret sharing scheme was presented at CHES 2011. It aims at providing security for hardware implementations - mainly of AES - against those sophisticated side-channel attacks that also take glitches into account. One part of this article deals with the practical issues and relevance of the aforementioned masking scheme. We first provide a guideline on how to implement the scheme for the simplest settings, and address some pitfalls in the scheme which prevent it to be practically realized. Solving the problems and constructing an exemplary design of the scheme, we provide practical side-channel evaluations based on a 65nm-technology Virtex-5 FPGA. We still observe univariate side-channel leakage, which is not expected according to the proven security of the scheme. We believe that the leakage is due to a combination of static power consumption and glitches in the circuit which is observed for the first time in practice. Dependency of static power consumption of nano-scale devices on processed data - which was warned before to be problematic - becomes now critical. Our result does not invalidate the given security proof of the scheme itself, but instead shows that the underlying model to obtain the proofs no longer fits to the reality. This is true not only for the scheme showcased here, but also for most other known masking schemes. As a result, due to the still ongoing technology shrinkage most of the available data-randomizing side-channel countermeasures will not be able to completely prevent univariate side-channel leakage of hardware implementations. Our work shows that new models must be created under which the security of new schemes can be proven considering leakages through both dynamic and static power consumption.