International Association for Cryptologic Research

# IACR News Central

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2013-01-12
10:17 [Pub][ePrint]

The simulation paradigm, introduced by Goldwasser, Micali and Rackoff, is of fundamental importance to modern cryptography. In a breakthrough work from 2001, Barak (FOCS\'01) introduced a novel non-black-box simulation technique. This technique enabled the construction of new cryptographic primitives, such as resettably-sound zero-knowledge arguments, that cannot be proven secure using just black-box simulation techniques.

The work of Barak and its follow-ups, however, all require stronger cryptographic hardness assumptions than the minimal assumption of one-way functions: the work of Barak requires the existence of collision-resistant hash functions, and a very recent result by Bitansky and Paneth (FOCS\'12) instead requires the existence of an Oblivious Transfer protocol.

In this work, we show how to perform non-black-box simulation assuming just the existence of one-way functions. In particular, we demonstrate the existence of a constant-round resettably-sound zero-knowledge argument based only on the existence of one-way functions. Using this technique, we determine necessary and sufficient assumptions for several other notions of resettable security of zero-knowledge proofs. An additional benefit of our approach is that it seemingly makes practical implementations of non-black-box zero-knowledge viable.

10:17 [Pub][ePrint]

An ever-increasing number of personal photos is stored online. This trend can be problematic, because face recognition software can undermine user privacy in unexpected ways. Face de-identification aims to prevent automatic recognition of faces thus improving user privacy, but previous work alters the image in a way that makes them indistinguishable for both computers and humans, which prevents a wide-spread use.

We propose a method for de-identification of images that effectively prevents face recognition software (using the most popular and effective algorithms) from identifying people, but still allows human recognition. We evaluate our method experimentally by adapting the CSU framework and using the FERET database. We show that we are able to achieve strong de-identification while maintaining reasonable image quality.

10:17 [Pub][ePrint]

In this short note, we demonstrate that the existence of one-way functions implies the existence of an $\\omega(1)$-round simultaneously resettable witness indistinguishable argument.

10:17 [Pub][ePrint]

Using simulated annealing, we derive several equivalence classes of balanced Boolean functions with optimum algebraic immunity, fast algebraic resistance, and maximum possible algebraic degree. For numbers n of input bits less than 16, these functions also possess superior nonlinearity to all Boolean functions so far obtained with said properties.

10:17 [Pub][ePrint]

We employ tropical algebras as platforms for several cryptographic

schemes that would be vulnerable to linear algebra attacks were they

based on usual\" algebras as platforms.

10:17 [Pub][ePrint]

Secure Multiparty Computation (SMC) enables a set of users to evaluate certain functionalities on their respective inputs while keeping these inputs encrypted throughout the computation. In many scenarios, however, outsourcing these computations to an untrusted server is desirable, so that the server can perform the computation on behalf of the users. Unfortunately, existing solutions are either inefficient, rely heavily on user interaction, or require the inputs to be encrypted under the same key - drawbacks making the employment in practice very limited.

We propose the first general-purpose construction that avoids all these drawbacks: it is efficient, it requires no user interaction whatsoever (except for data up- and download), and it allows evaluating any dynamically chosen function on inputs encrypted under different independent public keys. Our solution assumes the existence of two non-colluding but untrusted servers that jointly perform the computation by means of a cryptographic protocol. This protocol is provably secure in the semi-honest model. We demonstrate the applicability of our result in two real-world scenarios from different domains: Privacy-Preserving Face Recognition and Private Smart Metering. Finally, we give a performance analysis of our general-purpose construction to highlight its practicability.

2013-01-11
22:17 [Pub][ePrint]

NTRUEncrypt, proposed in 1996 by Hoffstein, Pipher and Silverman, is the fastest known lattice-based encryption scheme. Its moderate key-sizes, excellent asymptotic performance and conjectured resistance to quantum computers make it a desirable alternative to factorisation and discrete-log based encryption schemes. However, since its introduction, doubts have regularly arisen on its security and that of its digital signature counterpart. In the present work, we show how to modify NTRUEncrypt and NTRUSign to make them provably secure in the standard (resp. random oracle) model, under the assumed quantum (resp. classical) hardness of standard worst-case lattice problems, restricted to a family of lattices related to some cyclotomic fields.

Our main contribution is to show that if the secret key polynomials of the encryption scheme are selected from discrete Gaussians, then the public key, which is their ratio, is statistically indistinguishable from uniform over its range. We also show how to rigorously extend the encryption secret key into a signature secret key. The security then follows from the already proven hardness of the R-SIS and R-LWE problems.

22:17 [Pub][ePrint]

This paper is devoted to the design of a 258- bit multiplier for computing pairings over Barreto-Naehrig (BN) curves at 128-bit security level. The proposed design is optimized for Xilinx field programmable gate array (FPGA).

Each 258-bit integer is represented as a polynomial with five,65 bit signed integer, coefficients . Exploiting this splitting we designed a pipelined 65-bit multiplier based on new Karatsuba-Ofman variant using non-standard splitting to fit to the Xilinx embedded digital signal processor (DSP) blocks.

Our architecture is able to compute 258-bit multiplication suitable for BN curves using only 11 in-built DSP blocks available on Virtex-6

Xilinx FPGA devices. It is the least DSP blocks consumption in the known literature. This work can be extended to efficiently compute pairings at higher security levels.

22:17 [Pub][ePrint]

Recently, Isalam and Biswas proposed a new group key agreement (GKA) protocol for imbalanced mobile networks. In this letter, we will show that Isalam et al.\'s GKA protocol is not secure.

22:17 [Pub][ePrint]

We find a one to one correspondence between quadratic APN functions without linear and constant terms and a special kind of matrices (We call such matrices as QAMs). Based on the nice mathematical structures of the QAMs, we have developed efficient algorithms to construct quadratic APN functions. On $\\mathbb{F}_{2^7}$, we have found more than 470 classes of new CCZ-inequivalent quadratic APN functions, which is 20 times more than the known ones. Before this paper, there are only 23 classes of CCZ-inequivalent APN functions on $\\mathbb{F}_{2^{8}}$ have been found. With our method, we have found more than 1000 classes of new CCZ-inequivalent quadratic APN functions, and this number is still arising quickly.

2013-01-07
13:55 [Event][New]

Submission: 20 May 2013