International Association for Cryptologic Research

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10:16 [Job][New] Lecturer (Assistant/Associate Professor equivalent), University of Bristol, United Kingdom of Greater Britan and Norther Ireland, EU

  Four positions in Computer Science

  • Two in any area of CS

  • One in theory and algorithms

  • One in HCI

You will have demonstrated that you are on track to become an outstanding researcher, carrying out innovative research to complement that currently being pursued in the Department. You will have already achieved international recognition and have a significant number of high quality publications in top venues. Our strategy is to grow our research portfolio and you will be expected to take a major role in achieving that goal.

In addition, you will be expected to take an active role in providing high quality and innovative teaching in areas of Computer Science according to your experience. We are looking to enhance our teaching in core computer science; both theoretical aspects (such as formal methods, complexity, information theory, theory of programming languages, automated theorem proving/protocol analysis), as well as engineering aspects (such as programming languages, operating systems, distributed computing and software engineering). Interest in developing innovative ways of integrating teaching and research, and linking our teaching with the general computing industry, is particularly welcomed. The Department operates a reduced teaching load policy for new staff to enable their research activities to be established.

Please include in your CV and covering letter two one page statements; One on your research plans and how they will impact on the research profile of the Department and one on the contributions that you can make to teaching in the Department, especially in respect of innovation in delivery and content.

09:17 [Pub][ePrint] Secret and Verifiable Delegated Voting for Wide Representation, by Yefim Leifman

  This paper combines cryptographic voting and web page ranking and proves that it is possible to hold elections so as not to limit a voter by a list of candidates, to benefit from voter\'s personal experience in dealing with people, to make wide and proportional representation, and to achieve secrecy, including incoercibility, and verifiability of cryptographic voting systems.

09:17 [Pub][ePrint] Multi-Vendor PayWord with Payment Approval, by Andrea Huszti

  One of the most well known micropayment scheme is the PayWord scheme. It is designed to be onevendor, so if we apply it for multiple vendors, it does not protect against double spending. We extended the PayWord scheme, it supports shopping at multiple vendors without an on-line broker or an on-line secure database. The proposed credit-based system uses one hash chain, hence besides the secret signature key only the seed and a random value should be securely stored. Our scheme is analyzed in applied pi calculus, we prove that it fulfills payment approval, secure payment authorization, secrecy of payment information and unreusability.

18:17 [Pub][ePrint] Proposing Individualization of the design of cryptographic hardware accelerators as countermeasure against structure and side channel analysis, by Zoya Dyka, Thomas Basmer, Christian Wittke and Peter

  Side channel and fault attacks take advantage from the fact that the behavior of crypto implementations can be observed and provide hints that simplify revealing keys. These attacks are normally prepared by analyzing devices that are identical to the real target. Here we propose to individualize the design of cryptographic devices in order to prevent attacks that use identical devices. We implemented three different designs that provide exactly the same cryptographic function, i.e. an ECC kP multiplication. The synthesis and power simulation results show clear differences in the area consumed as well as in the power traces. We envision that this type of protection mechanism is relevant e.g. for wireless sensor networks from which devices can easily be stolen for further analysis in the lab.

18:17 [Pub][ePrint] New Results on Solving Linear Equations Modulo Unknown Divisors and its Applications, by Yao Lu and Rui Zhang and Dongdai Lin

  We revisit the problem of finding small solutions to a collection of linear equations modulo an unknown divisor $p$ for a known composite integer $N$. In Asiacrypt\'08, Herrmann and May introduced a heuristic algorithm for this problem, and their algorithm has many interesting applications, such as factoring with known bits problem, fault attacks on RSA signatures, etc. In this paper, we consider two variants of Herrmann-May\'s equations, and propose some new techniques to solve them. Applying our algorithms, we obtain a few by far the best analytical/experimental results for RSA and its variants. Specifically,


\\item We improve May\'s results (PKC\'04) on small secret exponent attack on RSA variant with moduli $N = p^rq$ ($r\\geq 2$).

\\item We extend Nitaj\'s result (Africacrypt\'12) on weak encryption exponents of RSA and CRT-RSA.


18:17 [Pub][ePrint] Toward Robust Hidden Volumes using Write-Only Oblivious RAM, by Erik-Oliver Blass and Travis Mayberry and Guevara Noubir and Kaan Onarlioglu

  With sensitive data being increasingly stored on mobile devices and

laptops, hard disk encryption is more important than ever. In

particular, being able to plausibly deny that a hard disk contains

certain information is a very useful and interesting research

goal. However, it has been known for some time that existing

``hidden volume\'\' solutions, like TrueCrypt, fail in the face of an

adversary who is able to observe the contents of a disk on multiple,

separate occasions. In this work, we explore more robust

constructions for hidden volumes and present HIVE, which is

resistant to more powerful adversaries with multiple-snapshot

capabilities. In pursuit of this, we propose the first security

definitions for hidden volumes, and prove HIVE secure under these

definitions. At the core of HIVE, we design a new write-only

Oblivious RAM. We show that, when only hiding writes, it is

possible to achieve ORAM with optimal O(1) communication complexity

and only poly-logarithmic user memory. This is a significant

improvement over existing work and an independently interesting

result. We go on to show that our write-only ORAM is specially

equipped to provide hidden volume functionality with low overhead

and significantly increased security. Finally, we implement HIVE as

a Linux kernel block device to show both its practicality and

usefulness on existing platforms.

18:17 [Pub][ePrint] Private Database Access With HE-over-ORAM Architecture, by Craig Gentry and Shai Halevi and Charanjit Jutla and Mariana Raykova

  Enabling private database queries is an important and challenging research problem with many real-world applications. The goal is for the client to obtain the results of its queries without learning anything else about the database, while the outsourced server learns nothing about the queries or data, including access patterns. The secure-computation-over-ORAM architecture offers a promising approach to this problem, permitting sub-linear time processing of the queries (after pre-processing) without compromising security.

In this work we examine the feasibility of this approach, focusing specifically on secure-computation protocols based on somewhat-homomorphic encryption (SWHE). We devised and implemented secure two-party protocols in the semi-honest model for the path-ORAM protocol of Stefanov et al. This provides access by index or keyword, which we extend (via pre-processing) to limited conjunction queries and range queries. Some of our sub-protocols may be interesting in their own right, such as our new protocols for encrypted comparisons and blinded permutations.

We implemented our protocols on top of the HElib homomorphic encryption library. Our basic single-threaded implementation takes about 30 minutes to process a query on a database with $2^{22}$ records and 120-bit long keywords, providing a cause for optimism about the viability of this direction, and we expect a better optimized implementation to be much faster.

18:17 [Pub][ePrint] Time-Memory Trade-offs for Index Calculus in Genus 3, by Kim Laine and Kristin Lauter

  In this paper, we present a variant of Diem\'s $\\widetilde{O}(q)$ index calculus algorithm to attack the discrete logarithm problem (DLP) in Jacobians of genus 3 non-hyperelliptic curves over a finite field $\\mathbb{F}_q$. We implement this new variant in C++ and study the complexity in both theory and practice, making the logarithmic factors and constants hidden in the $\\widetilde{O}$-notation precise.

Our variant improves the computational complexity at the cost of a moderate increase in memory consumption, but we also improve the computational complexity even when we limit the memory usage to that of Diem\'s original algorithm. Finally, we examine how parallelization can help to reduce both the memory cost per computer and the running time for our algorithms.

18:17 [Pub][ePrint] One-Way Functions and (Im)perfect Obfuscation, by Ilan Komargodski and Tal Moran and Moni Naor and Rafael Pass and Alon Rosen and Eylon Yogev

  A program obfuscator takes a program and outputs an \"scrambled\" version of it, where the goal is that the obfuscated program will not reveal much

about its structure beyond what is apparent from executing it. There are several ways of formalizing this goal. Specifically, in

indistinguishability obfuscation, first defined by Barak et al. (CRYPTO 2001), the requirement is that the results of obfuscating any two

functionally equivalent programs (circuits) will be computationally indistinguishable. Recently, a fascinating candidate construction for

indistinguishability obfuscation was proposed by Garg et al. (FOCS 2013). This has led to a flurry of discovery of intriguing constructions of

primitives and protocols whose existence was not previously known (for instance, fully deniable encryption by Sahai and Waters, STOC 2014). Most

of them explicitly rely on additional hardness assumptions, such as one-way functions.

Our goal is to get rid of this extra assumption. We cannot argue that indistinguishability obfuscation of all polynomial-time circuits implies

the existence of one-way functions, since if $P = NP$, then program obfuscation (under the indistinguishability notion) is possible. Instead, the

ultimate goal is to argue that if $P \\neq NP$ and program obfuscation is possible, then one-way functions exist.

Our main result is that if $NP \\not\\subseteq ioBPP$ and there is an efficient (even imperfect) indistinguishability obfuscator, then there are

one-way functions. In addition, we show that the existence of an indistinguishability obfuscator implies (unconditionally) the existence of SZK-

arguments for NP. This, in turn, provides an alternative version of our main result, based on the assumption of hard-on-the average NP problems.

To get some of our results we need obfuscators for simple programs such as CNF formulas.

18:17 [Pub][ePrint] A Simple Cast-as-Intended E-Voting Protocol by Using Secure Smart Cards, by Helger Lipmaa

  We propose a simple cast-as-intended remote e-voting protocol where the security is based on the use of secure (and trusted) smart cards that incorporate incard numeric keyboards and LCD displays, and can perform a limited number of cryptographic operations (like encryption, signing, and random number generation). The protocol, while very simple, is significantly more secure (in the sense of ``cast-as-intended\'\') and convenient to use than the e-voting protocol currently used in Norway. The protocol is developed primarily with the idea of deploying it in Estonia within the next $3$ to $10$ years. Since in Estonia, a vast majority of the population already has ID-cards with digital signing and authentication functionality, and the use of ID-cards is a required prerequisite to participate in Estonian e-voting anyway, our assumption of every voter having a secure hardware token makes sense in this concrete context.

18:17 [Pub][ePrint] Zerocash: Decentralized Anonymous Payments from Bitcoin, by Eli Ben-Sasson and Alessandro Chiesa and Christina Garman and Matthew Green and Ian Miers and Eran Tromer and Madars Virza

  Bitcoin is the first digital currency to see widespread adoption. While payments are conducted between pseudonyms, Bitcoin cannot offer strong privacy guarantees: payment transactions are recorded in a public decentralized ledger, from which much information can be deduced. Zerocoin (Miers et al., IEEE S&P 2013) tackles some of these privacy issues by unlinking transactions from the payment\'s origin. Yet, it still reveals payments\' destinations and amounts, and is limited in functionality.

In this paper, we construct a full-fledged ledger-based digital currency with strong privacy guarantees. Our results leverage recent advances in zero-knowledge Succinct Non-interactive ARguments of Knowledge (zk-SNARKs).

First, we formulate and construct decentralized anonymous payment schemes (DAP schemes). A DAP scheme enables users to directly pay each other privately: the corresponding transaction hides the payment\'s origin, destination, and transferred amount. We provide formal definitions and proofs of the construction\'s security.

Second, we build Zerocash, a practical instantiation of our DAP scheme construction. In Zerocash, transactions are less than 1 kB and take under 6 ms to verify --- orders of magnitude more efficient than the less-anonymous Zerocoin and competitive with plain Bitcoin.