International Association for Cryptologic Research

# IACR News Central

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2012-08-18
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.

06:17 [Pub][ePrint]

The first sender equivocable encryption scheme secure against chosen-ciphertext attack (NC-CCA) was proposed by Fehr et al. in Eurocrypt 2010. The scheme was also secure against selective opening chosen-ciphertext attack (SO-CCA), since NC-CCA security implies SO-CCA security.

The NC-CCA security proof of the scheme relies on security against substitution attack of a new primitive, cross-authentication code\'\'. However, the security of cross-authentication code can not guarantee anything when all the keys used in the code are exposed. The key observation is that in the NC-CCA game, the randomness used in the generation of the challenge ciphertext is exposed to the adversary. This random information can be used to recover all the keys involved in cross-authentication code, and forge a ciphertext (like a substitution attack of cross-authentication code) that is different from but related to the challenge ciphertext. And the response of decryption oracle leaks information. This leaked information is employed by an attack to spoil the NC-CCA security proof of the sender equivocable encryption scheme encrypting multi-bits. We also propose a new scheme encrypting single-bit plaintext, free of cross-authentication code, and prove its NC-CCA security.

06:17 [Pub][ePrint]

Functional encryption (FE) is a powerful cryptographic primitive that generalizes many asymmetric encryption systems proposed in recent years. Syntax and security definitions for general FE were recently proposed by Boneh, Sahai, and Waters (BSW) (TCC 2011) and independently by O\'Neill (ePrint 2010/556). In this paper we revisit these definitions, identify a number of shortcomings in them, and propose a new definitional approach that overcomes these limitations. Our definitions display good compositionality properties and allow us to obtain new feasibility and impossibility results for adaptive token extraction attack scenarios that shed further light on the potential reach of general FE for practical applications. The main contributions of the paper are the following:

- We show that the BSW definition of semantic security fails to reject intuitively insecure FE schemes where a ciphertext leaks more about an encrypted message than that which can be recovered from an image under the supported functionality. Our definition (as O\'Neill\'s) does not suffer from this problem.

- We introduce an orthogonal notion of {\\em setup security} that rejects all FE schemes where the master secret key may give unwanted power to the TA, allowing the recovery of extra information from images under the supported functionality. We prove FE schemes supporting {\\em all-or-nothing} functionalities are intrinsically setup-secure and further show that many well-known functionalities {\\em are} all-or-nothing.

- We extend the equivalence result of O\'Neill between indistinguishability and semantic security to restricted {\\em adaptive} token extraction attacks (the standard notion of security for, e.g., IBEs and ABEs). We establish that this equivalence holds for the large class of all-or-nothing functionalities. Conversely, we show that the proof technique used to establish this equivalence cannot be applied to schemes supporting a one-way function.

- We show that the notable {\\em inner-product} functionality introduced by Katz, Sahai, and Waters (EUROCRYPT 2008) can be used to encode a one-way function under the small integer solution problem, and hence natural approaches to prove its (restricted) adaptive security fail. This complements the equivalence result of O\'Neill for the non-adaptive case, and leaves open the question of proving the semantic security of existing inner-product encryption schemes.

06:17 [Pub][ePrint]

Direct Anonymous Attestation (DAA) is one of the most complex cryptographic protocols deployed in practice.

It allows an embedded secure processor known as a Trusted Platform Module (TPM) to attest to the configuration of its host computer without violating the owner\'s privacy.

DAA has been standardized by the Trusted Computing Group.

The security of the DAA standard and all existing schemes is analyzed in the random oracle model.

We provide the first constructions of DAA in the standard model, that is, without relying on random oracles.

As a building block for our schemes, we construct the first efficient standard-model signatures of knowledge, which have many applications beyond DAA.

2012-08-17
05:12 [Job][New]

Japan Advanced Institute of Science and Technology (JAIST) invites applicants to a five-year term assistant professor position in SCHOOL OF INFORMATION SCIENCE. The appointee is expected to start her/his academic and educational activities in JAIST on April 1st, 2013.

A primary objective of this position is to promote international research and development activities in Cryptology and Information Security, where candidates have to be highly competent in conducting research work.

Applicants have to hold Ph.D degree, and be qualified for high scientific activities through participating in international research initiatives. The salary is automatically decided depending on your experiences and age (Typical example of annual income is about 4,000,000 to 5,000,000 yen per year (including tax)). Security group in JAIST can research by making full use of the advanced parallel computer system.

2012-08-16
20:55 [Event][New]

Submission: 7 October 2012
From December 2 to December 2

07:59 [Event][New]

Submission: 8 September 2012
From February 25 to February 27
Location: Cape Town, South Africa

07:59 [Event][New]

Submission: 27 August 2012
From January 29 to February 1

07:58 [Job][New]

Topic: Lattice-based cryptography

Supervisor: Prof. Steven Galbraith

Duration: Approx 18-24 months

Salary: Approx NZ$55,000-70,000 (US$ 44K-56K) depending on the experience of the candidate and other factors

Start date: Preferably between November 2012-March 2013

Application process:

There is no formal application process. If you are interested in learning more about the position then please send a copy of your CV by email to s.galbraith (at) math.auckland.ac.nz , preferably before September 8, 2012.

Project Details:

The project will be on the security and implementation of lattice-based cryptosystems. The specific topic of the research will depend on the technical skills and experience of the successful candidate. Some possible projects might include:

• development and analysis of algorithms for lattice problems

• development and security analysis of lattice-based cryptosystems

• efficient software and/or hardware implementation of lattice systems

The successful applicant will have (or be very near to completion) a PhD in mathematics/computer science/engineering and a research track record in at least one of the following areas:

• theoretical cryptography

• computational number theory and lattices

• software/hardware implementation of cryptographic systems.