International Association for Cryptologic Research

# IACR News Central

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2012-12-18
13:17 [Pub][ePrint]

We introduce the notion of covert security with public verifiability, building on the covert security model introduced by Aumann and Lindell (TCC 2007). Protocols that satisfy covert security guarantee that the honest parties involved in the protocol will notice any cheating attempt with some constant probability $\\epsilon$. The idea behind the model is that the fear of being caught cheating will be enough of a deterrent to prevent any cheating attempt. However, in the basic covert security model, the honest parties are not able to persuade any third party (say, a judge) that a cheating occurred.

We propose (and formally define) an extension of the model where, when an honest party detects cheating, it also receives a certificate that can be published and used to persuade other parties, without revealing any information about the honest party\'s input. In addition, malicious parties cannot create fake certificates in the attempt of framing innocents.

Finally, we construct a secure two-party computation protocol for any functionality $f$ that satisfies our definition, and our protocol is almost as efficient as the one of Aumann and Lindell. We believe that the fear of a public humiliation or even legal consequences vastly exceeds the deterrent given by standard covert security. Therefore, even a small value of the deterrent factor $\\epsilon$ will suffice in discouraging any cheating attempt.

As the overall complexity of covert security and the parameter $\\epsilon$ are inversely proportional to each other, we believe that the small price to pay to get the public verifiability property on top of covert security will be dominated by the efficiency gain obtained by using a smaller value $\\epsilon$.

2012-12-17
14:09 [Job][New]

LACS at the University of Luxembourg is looking for a post-doctoral researcher in the area of lightweight cryptography. The successful candidate will contribute to a research project entitled Applied Cryptography for the Internet of Things (ACRYPT), which is funded by the Fonds National de la Recherche (FNR). Besides conducting high-quality research, the tasks associated with this position include the co-supervision of a Ph.D. student and the dissemination of research results. The ACRYPT project is led by Prof. Alex Biryukov and expected to start in summer 2013.

Candidates must hold a Ph.D. degree (or be in the final stages of a Ph.D. program) in cryptography or a closely related discipline. Applications from researchers with experience in embedded systems security, network security, privacy/anonymity, or mobile/wireless security will also be considered. Preference will be given to candidates with a strong publication record including papers in top-tier crypto/security conference proceedings or journals. Candidates with an interest to conduct leading-edge research in one of the following areas are particularly encouraged to apply:

• Design and analysis of symmetric cryptographic primitives
• Efficient implementation of cryptosystems in hardware and/or software
• Physical attacks (SPA, DPA, fault attacks, etc.) and countermeasures

The position is offered on basis of a fixed-term contract for a duration of three years, which includes a probation period of six months. The monthly salary is roughly 3,600 € net (i.e. after deduction of taxes and social security contributions). Interested candidates are invited to submit their application by email to lacs.acrypt(at)gmail.com. The application material should contain a cover letter explaining the candidate\'s motivation and research interests, a detailed CV (including photo), a list of publications, copies of diploma certificates, and names and contact detai

07:01 [Event][New]

Submission: 15 January 2013
From July 3 to July 5
Location: Taichung, Taiwan

2012-12-15
13:12 [Event][New]

Submission: 17 March 2013
From July 10 to July 12
Location: Tarragona, Catalonia, Spain

13:11 [Job][Update]

The Government Communications Headquarters (GCHQ) in Cheltenham has agreed in principle to sponsor a PhD/Doctoral Studentship at CSIT, Queens University Belfast in the area of Novel Application of Advanced Machine Learning Techniques for use in Side Channel Analysis Attacks.

This GCHQ-sponsored PhD studentship provides funding for 3.5 years and commences on 31 September 2013 with a proposed end date of March/April 2017. GCHQ will cover the costs of university fees and will provide an annual stipend to the student corresponding to the National Minimum Stipend (currently £13,590 per annum) plus an additional sum of £7,000 per annum (both tax free). For comparison this is equivalent to approx. £26,555 annual salary. A further £5k of funding will also be available per annum for travel to conferences, collaborative partners, and GCHQ visits.

The studentship is only open to UK nationals and the successful candidate will be required to spend in the region of 2 - 4 weeks per year at GCHQ headquarters in Cheltenham. To be considered for this studentship, candidates must therefore be prepared to undergo GCHQ\\\'s security clearance procedures.

13:11 [Job][New]

The Government Communications Headquarters (GCHQ) in Cheltenham has agreed in principle to sponsor a PhD/Doctoral Studentship at CSIT, Queens University Belfast in the area of Novel Application of Advanced Machine Learning Techniques for use in Side Channel Analysis Attacks.

This GCHQ-sponsored PhD studentship provides funding for 3.5 years and commences on 31 September 2013 with a proposed end date of March/April 2017. GCHQ will cover the costs of university fees and will provide an annual stipend to the student corresponding to the National Minimum Stipend (currently £13,590 per annum) plus an additional sum of £7,000 per annum (both tax free). For comparison this is equivalent to approx. £26,555 annual salary. A further £5k of funding will also be available per annum for travel to conferences, collaborative partners, and GCHQ visits.

The studentship is only open to UK nationals and the successful candidate will be required to spend in the region of 2 - 4 weeks per year at GCHQ headquarters in Cheltenham. To be considered for this studentship, candidates must therefore be prepared to undergo GCHQ\'s security clearance procedures.

2012-12-14
22:17 [Pub][ePrint]

RAKAPOSHI is a hardware oriented stream cipher designed by Carlos Cid et al. in 2009. The stream cipher is based on Dynamic Linear Feedback Shift Registers, with a simple and potentially scalable design, and is particularly suitable for hardware applications with restricted resources. The RAKAPOSHI stream cipher offers 128-bit security. In this paper, we point out some weaknesses in the cipher. Firstly, it shows that there are 2^192 weak (key, IV) pairs in RAKAPOSHI stream cipher. Secondly, for weak (key, IV) pairs of RAKAPOSHI, they are vulnerable to linear distinguishing attack and algebraic attack. Finally, we propose a real time related key chosen IV attack on RAKAPOSHI. The attack on RAKAPOSHI recovers the 128-bit secret key of with a computational complexity of 2^37, requiring 47 related keys, 2^8 chosen IVs and 2^14.555 keystream bits. The success probability of this attack is 0.999, which is quite close to 1. The experimental results corroborate our assertion.

22:17 [Pub][ePrint]

In order to guarantee a fair and transparent voting process, electronic voting schemes must be verifiable. Most of the time, however, it is important that elections also be anonymous. The notion of a verifiable shuffle describes how to satisfy both properties at the same time: ballots are submitted to a public bulletin board in encrypted form, verifiably shuffled by several mix servers (thus guaranteeing anonymity), and then verifiably decrypted by an appropriate threshold decryption mechanism. To guarantee transparency, the intermediate shuffles and decryption results, together with proofs of their correctness, are posted on the bulletin board throughout this process.

In this paper, we present a verifiable shuffle and threshold decryption scheme in which, for security parameter k, L voters, M mix servers, and N decryption servers, the proof that the end tally corresponds to the original encrypted ballots is only O(k(L + M + N)) bits long. Previous verifiable shuffle constructions had proofs of size O(kLM + kLN), which, for elections with thousands of voters, mix servers, and decryption servers, meant that verifying an election on an ordinary computer in a reasonable amount of time was out of the question.

The linchpin of each construction is a controlled-malleable proof (cm-NIZK), which allows each server, in turn, to take a current set of ciphertexts and a proof that the computation done by other servers has proceeded correctly so far. After shuffling or partially decrypting these ciphertexts, the server can also update the proof of correctness, obtaining as a result a cumulative proof that the computation is correct so far. In order to verify the end result, it is therefore sufficient to verify just the proof produced by the last server.

22:17 [Pub][ePrint]

In this paper we consider the problem of secure pattern matching that allows

single-character wildcards and substring matching in the malicious (stand-alone) setting.

Our protocol, called 5PM, is executed between

two parties: Server, holding a text of length $n$, and

Client, holding a pattern of length $m$ to be matched

against the text, where our notion of matching is more general and includes non-binary alphabets, non-binary Hamming distance and non-binary substring matching.

5PM is the first secure expressive pattern matching protocol designed to optimize round complexity by carefully specifying the entire protocol round by round. In the malicious model, 5PM requires $O((m+n)k^2)$ bandwidth and $O(m+n)$ encryptions, where $m$ is the pattern length and $n$ is the text length. Further, 5PM can hide pattern size with no asymptotic additional costs in either computation or bandwidth. Finally, 5PM requires only two rounds of communication

in the honest-but-curious model and eight rounds in the malicious model. Our techniques reduce

pattern matching and generalized Hamming distance problems to a novel linear algebra formulation that allows for generic solutions based on any additively homomorphic encryption. We believe our efficient algebraic techniques are of independent interest.

22:17 [Pub][ePrint]

We conduct a practically oriented study of the cryptosystem suggested by Alekhnovich based on the Learning Parity with Noise (LPN) problem. We consider several improvements to the scheme, inspired by similar existing variants of Regev\'s LWE-based cryptosystem. Our conclusion is that LPN-based public-key cryptography indeed seems practical. Based on known attacks on LPN, we found that for 80-bit security, while making very conservative choices of parameters for LPN, the timings for transmitting a key for a symmetric cryptosystem are somewhat worse than for RSA, but not prohibitive for practical use.

22:17 [Pub][ePrint]

We present a general framework for efficient, universally composable oblivious transfer (OT) protocols in which a single, global common reference string (CRS) can be used for multiple invocations of oblivious transfer, by arbitrary pairs of parties. In addition:

* Our framework is round-efficient. In particular, under the DLIN or SXDH assumptions we achieve (round-optimal) two-round protocols with static security, or three-round protocols with adaptive security (assuming erasure).

* Our protocols are more efficient than any known previously, and in particular yield protocols for string OT using O(1) exponentiations and sending O(1) group elements. Our result improves upon that of Peikert et al. (Crypto 2008) which requires a CRS of length

linear in the number of parties and achieves only static security. Compared to Garay et al. (Crypto 2009), we achieve better efficiency and can rely on a larger class of assumptions.