International Association for Cryptologic Research

# IACR News Central

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2014-04-07
10:55 [Job][New]

The Reliable Communication Group at the University of Bergen invites applications for a 3-year researcher position in Boolean functions. The position is supposed to start in October 2014.

The candidate is expected to have PhD degree in mathematics or computer science or related disciplines, and have considerable publications in discrete functions.

We are seeking an active researcher with expertise in Boolean functions, discrete mathematics and symmetric cryptography to work within the recently funded project “Discrete functions and their applications in cryptography and mathematics”. The prime objectives of this project are Boolean functions with optimal resistance to various cryptographic attacks (differential, linear, algebraic et al.) and their applications in discrete mathematics (such as commutative semifields, o-polynomials, difference sets, dual hyperovals, regular graphs, m-sequences, codes et al.).

2014-04-05
18:17 [Pub][ePrint]

Achterbahn stream cipher is proposed as a candidate for ECRYPT eSTREAM project which deals with key of length 80-bit. The linear distinguishing attack,which aims at distinguishing the keystream from purely random keystream,is employed to Achterbahn stream cipher. A linear distinguishing attack is based on linear sequential circuit approximation technique which distinguishes statistical bias in the keystream. In order to build the distinguisher, linear approximations of both non-linear feedback shift register (NLFSR) and the non-linear Boolean combining function R:F_2^8→F_2 are used. The keystream sequence generated by this algorithm consist a distinguisher with its probability bias〖 2〗^(-1809). Thus, to distinguish the Achterbahn, we only need 1/ε^2 =〖〖(2〗^1809)〗^2=2^3618 keystream bits and the time complexity is about 10/ε^2 =2^3621.3 which is much higher than the exhaustive key search O(2^80).

2014-04-03
15:32 [Job][New]

The Engineering Cryptographic Protocols Group at TU Darmstadt is looking for a doctoral student in Engineering Cryptographic Protocols for Cloud Computing.

Our group is involved in the two main research centers for IT security in Darmstadt, the Center for Advanced Security Research Darmstadt (CASED) and the European Center for Security and Privacy by Design (EC SPRIDE). We develop new methods and tools to optimize and automatically generate cryptographic protocols. See http://encrypto.de for details.

The candidate will work in the EU FP 7 research project PRACTICE (Privacy-Preserving Computation in the Cloud), http://www.practice-project.eu, with the goal of developing, optimizing, and automatically generating secure computation protocols for cloud computing.

The candidate is expected to have a completed Master (or equivalent) degree with excellent grades in IT security, computer science, electrical engineering, mathematics, or a closely related field. Solid knowledge in IT security, applied cryptography, and programming skills is required. Additional knowledge in cryptographic protocols, parallel computing, compiler construction, programming languages, and software engineering is a plus.

Review of applications starts immediately until the position is filled.

Please consult the webpage given below for more details and how to apply.

2014-04-02
17:11 [Event][New]

Submission: 1 June 2014
From September 1 to September 2
Location: Istanbul, Turkey

17:10 [Event][New]

Submission: 20 May 2014
From September 10 to September 11
Location: Wroclaw, Poland

2014-04-01
09:17 [Pub][ePrint]

The ZigBee specification is an emerging wireless technology designed to address the specific needs of low-cost, low-power wireless sensor networks and is built upon the physical and medium access control layers defined in IEEE 802.15.4 standard for wireless personal area networks (WPANs). A key component for the wide-spread success and applicability of ZigBee-based networking solutions will be its ability to provide enhanced security mechanisms that can scale to hundreds of nodes. Currently, however, an area of concern is the ZigBee key management scheme, which uses a centralized approach that introduces well-known issues of limited scalability and a single point of vulnerability. Moreover, ZigBee key management uses a public key infrastructure. Due to these limitations, we suggest replacing ZigBee key management with a better candidate scheme that is decentralized, symmetric, and scalable while addressing security requirements. In this work, we investigate the feasibility of implementing Localized Encryption and Authentication Protocol (LEAP+), a distributed symmetric based key management. LEAP+ is designed to support multiple types of keys based on the message type that is being exchanged. In this paper, we first conduct a qualitative security analysis of LEAP+ and the current ZigBee key management scheme. Using the QualNet 5.0.2 simulator, we implement LEAP+ on the ZigBee platform for the very first time. Experimental results show that a distributed key management scheme such as LEAP+ provides improved security and offers good scalability.

09:17 [Pub][ePrint]

An isogeny graph is a graph whose vertices are principally polarized

abelian varieties and whose edges are isogenies between these varieties. In

his thesis, Kohel described the structure of isogeny graphs for elliptic

curves and showed that one may compute the endomorphism ring of an elliptic

curve defined over a finite field by using a depth first search algorithm

in the graph. In dimension 2, the structure of isogeny graphs is less understood and existing algorithms for computing endomorphism rings are very expensive.

Our setting considers genus 2 jacobians with complex multiplication,

with the assumptions that the real multiplication subring is maximal and

has class number one. We fully describe the isogeny graphs in that

case.

Over finite fields, we derive a depth first search algorithm for computing endomorphism rings locally at prime numbers, if the real multiplication is maximal. To the best of our knowledge, this is the first DFS-based algorithm in genus 2.

09:17 [Pub][ePrint]

Cloud storage is very popular since it has many advantages, but there is a new threat to cloud storage that was not considered before. {\\it Self-updatable encryption} that updates a past ciphertext to a future ciphertext by using a public key is a new cryptographic primitive introduced by Lee, Choi, Lee, Park, and Yung (Asiacrypt 2013) to defeat this threat such that an adversary who obtained a past-time private key can still decrypt a (previously unread) past-time ciphertext stored in cloud storage. Additionally, an SUE scheme can be combined with an attribute-based encryption (ABE) scheme to construct a powerful revocable-storage ABE (RS-ABE) scheme introduced by Sahai, Seyalioglu, and Waters (Crypto 2012) that provides the key revocation and ciphertext updating functionality for cloud storage.

In this paper, we propose an efficient SUE scheme and its extended schemes. First, we propose an SUE scheme with short public parameters in prime-order bilinear groups and prove its security under a $q$-type assumption. Next, we extend our SUE scheme to a time-interval SUE (TI-SUE) scheme that supports a time interval in ciphertexts. Our TI-SUE scheme has short public parameters and also secure under the $q$-type assumption. Finally, we propose the first large universe RS-ABE scheme with short public parameters in prime-order bilinear groups and prove its security in the selective revocation list model under a $q$-type assumption.

09:17 [Pub][ePrint]

We present a private information retrieval (PIR) scheme based on a somewhat homomorphic encryption (SWHE). In particular, we customize an NTRU-based SWHE scheme in order to evaluate a specific class of fixed depth circuits relevant for PIR implementation, thus achieving a more practical implementation. In practice, a SWHE that can evaluate a depth 5 circuit is sufficient to construct a PIR capable of retrieving data from a database containing 4 billion rows. We leverage this property in order to produce a more practical PIR scheme. Com- pared to previous results, our implementation achieves a significantly lower bandwidth cost (more than 1000 times smaller). The computational cost of our implementation is higher than previous proposals for databases containing a small number of bits in each row. However, this cost is amortized as database rows become wider.

09:17 [Pub][ePrint]

We present the homomorphic evaluation of the Prince block cipher. Our leveled implementation is based on a generalization of NTRU. We are motivated by the drastic bandwidth savings that may be achieved by scheme conversion. To unlock this advantage we turn to lightweight ciphers such as Prince. These ciphers were designed from scratch to yield fast and compact implementations on resource constrained embedded platforms. We show that some of these ciphers have the potential to enable near practical homomorphic evaluation of block ciphers. Indeed, our analysis shows that Prince can be implemented using only a 24 level deep circuit. Using an NTRU based implementation we achieve an evaluation time of 3.3 seconds per Prince block - one and two orders of magnitude improvement over homomorphic AES implementations achieved using NTRU, and BGV-style homomorphic encryption libraries, respectively.

09:17 [Pub][ePrint]

Oblivious RAM (ORAM) is an established technique to hide the access pattern to an untrusted storage system.

With ORAM, a curious adversary cannot tell what data address the user is accessing when observing the bits moving between the user and the storage system.

All existing ORAM schemes achieve obliviousness by adding redundancy to the storage system, i.e., each access is turned into multiple random accesses.

Such redundancy incurs a large performance overhead.

Though traditional data prefetching techniques successfully hide memory latency in DRAM based systems, it turns out that they do not work well for ORAM.

In this paper, we exploit ORAM locality by taking advantage of the ORAM internal structures.

Though it might seem apparent that obliviousness and locality are two contradictory concepts, we challenge this intuition by exploiting data locality in ORAM without sacrificing provable security.

In particular, we propose an ORAM prefetching technique called dynamic super block scheme and comprehensively explore its design space.

The dynamic super block scheme detects data locality in the program\'s working set at runtime, and exploits the locality in a data-independent way.

% based on the key observation that position map ORAMs have better locality than the data ORAM.

Our simulation results show that with dynamic super block scheme, ORAM performance without super blocks can be significantly improved. After adding timing protection to ORAM, the average performance gain is 25.5\\% (up to 49.4\\%) over the baseline ORAM and 16.6\\% (up to 30.1\\%) over the best ORAM prefetching technique proposed previously.