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2013-03-26
15:17 [Pub][ePrint]

How can we encode a communication protocol between two parties to become resilient to adversarial errors on the communication channel? This question dates back to the seminal works of Shannon and Hamming from the 1940\'s, initiating the study of error-correcting codes (ECC). But, even if we encode each message in the communication protocol with a good\'\' ECC, the error rate of the encoded protocol becomes poor (namely $O(1/m)$ where $m$ is the number of communication rounds). Towards addressing this issue, Schulman (FOCS\'92, STOC\'93) introduced the notion of \\emph{interactive coding}.

We argue that whereas the method of separately encoding each message with an ECC ensures that the encoded protocol carries the same amount of information as the original protocol, this may no longer be the case if using interactive coding. In particular, the encoded protocol may completely leak a player\'s private input, even if it would remain secret in the original protocol. Towards addressing this problem, we introduce the notion of \\emph{knowledge-preserving interactive coding}, where the interactive coding protocol is required to preserve the knowledge\'\' transmitted in the original protocol. Our main results are as follows.

\\begin{itemize}

\\item The method of separately applying ECCs to each message is essentially optimal: No knowledge-preserving interactive coding scheme can have an error rate of $1/m$, where $m$ is the number of rounds in the original protocol.

\\item If restricting to computationally-bounded (polynomial-time) adversaries, then assuming the existence of one-way functions (resp. subexponentially-hard one-way functions), for every $\\epsilon>0$, there exists a knowledge-preserving interactive coding schemes with constant error rate and information rate $n^{-\\epsilon}$ (resp. $1/\\polylog(n)$) where $n$ is the security parameter; additionally to achieve an error of even $1/m$ requires the existence of one-way functions.

\\item Finally, even if we restrict to computationally-bounded adversaries, knowledge-preserving interactive coding schemes with constant error rate can have an information rate of at most $o(1/\\log n)$. This results applies even to \\emph{non-constructive} interactive coding schemes.

\\end{itemize}

15:17 [Pub][ePrint]

Since Kilian showed in 1988 that oblivious transfer (OT) is complete in the sense that every secure multi-party computation can be realized from this primitive, cryptographers are working on reduction of OT to various other primitives. A long standing open question in this context is the classification of finite stateless 2-party primitives (so-called \"cryptogates\"), i.e. trusted black boxes that can be jointly queried by two parties, have finite input and output alphabets, and do not change behavior depending on time or input history. Over the decades, completeness criteria have been found for deterministic cryptogates (i.e. primitives without internal randomness), noisy channels, and symmetric (i.e., both parties receive the same output) or asymmetric (i.e., only one party receives any output at all) randomized cryptogates. However, the known criteria for randomized primitives other than noisy channels only hold in presence of passive adversaries (i.e., even corrupted parties still follow the protocol).

We complete this line of research by providing simple but comprehensive combinatorial completeness criteria for ALL finite stateless 2-party primitives. I.e., for the first time there are completeness criteria for randomized primitives that are neither symmetric nor asymmetric (but give different outputs to the querying parties), and we overcome the limitation that previous results for randomized primitives with input from BOTH parties only regarded passive adversaries. A fundamental tool of our approach is a powerful lemma from real algebraic geometry, which allows us to base a cryptographic security proof on a rather \"game-theoretic\" approach.

As a corollary of our work, every non-complete example of a finite stateless 2-party primitive is essentially symmetric. This relationship between non-completeness and symmetric output behavior was previously only known for deterministic cryptogates.

15:17 [Pub][ePrint]

We propose here a non asymptotic complexity analysis of

some variants of information set decoding. In particular, we give this

analysis for the two recent variants { published by May, Meurer and

Thomae in 2011 and by Becker, Joux, May and Meurer in 2012 { for

which only an asymptotic analysis was available. The purpose is to

provide a simple and accurate estimate of the complexity to facilitate

the paramater selection for code-based cryptosystems. We implemented

those estimates and give a comparison at the end of the paper.

15:17 [Pub][ePrint]

Searching on remote encrypted data (commonly known as \\textit{searchable encryption}) is becoming an important technique in secure data outsourcing, since it allows users to outsource encrypted data to the third party and maintains the keyword searching on the data at the same time.

It has been widely accepted in the literature that searchable encryption techniques should leak as little information as possible to the third party. An early classical method called oblivious RAM hides all information at the cost of poly-logarithmic computation and communication overheads, which turns out to be impractical in the real world applications (e.g., cloud computing). A number of efficient searchable encryption schemes have been proposed under weaker security guarantees afterwards, however, such schemes leak statistical information about the user\'s search pattern.

In this paper, we show that the search pattern leakage can result in non-trivial risks. As pioneer work, we present two concrete attack models exploiting user\'s search pattern and some auxiliary background knowledge aiming to disclose the underlying keywords of user\'s queries. To resist these attacks, we develop two new searchable encryption constructions that hide the search pattern. Our constructions are designed to be independent from the underlying searchable encryption scheme. Our experiments, which are based on the real world dataset, demonstrate the effectiveness and efficiency of proposed attack models and new constructions.

15:17 [Pub][ePrint]

In this paper we present the (to the best of our knowledge) first LWE-based encryption scheme that removes the need of Gaussian sampling for the error, i.e. the discrete Gaussian distribution is replaced by the uniform distribution on a (small) set, which at the same time preserves the underlying worst-case hardness. This shows that provable security and efficiency do not necessarily have to mutually exclude each other. We give an asymptotic parameter instantiation for our scheme, as well as some hardness results for LWE which might be of independent interest.

2013-03-25
15:31 [Event][New]

Submission: 8 May 2013
From June 20 to June 21
Location: Leuven, Belgium

15:29 [Event][New]

Submission: 1 July 2013
From September 20 to September 21
Location: Ankara, Turkey

15:29 [Event][New]

Submission: 3 June 2013
From October 23 to October 25
Location: La Rochelle, France

15:28 [Event][New]

From May 4 to May 8
Location: Copenhagen, Denmark

15:27 [Job][New]

ESCRYPT is a leading company in the area of applied data security. Our clients include all global auto makers as well as leading global players in the area of machinery, automation, semiconductors and high-tech companies.

Develop customized software for client projects in the areas concerning embedded data security and engage in product development; Design various software applications including the design of secure systems, specification of Application Programming Interfaces (API) development of software in typical programming languages C, C++, Java) and use of development environments (e.g. Eclipse); Maintain and develop documentation and testing of the developed software; Apply cryptographic mechanisms (e.g. RSA, Elliptic Curve Cryptography and AES) and of security protocols such as TLS; Provide solutions to clients and educating same to properly use the software. The position requires familiarity in the use of Windows and Linux, and in the set-up of a development environment (e.g. setting up an environment with virtual machines and databases). The position also requires rationalizing design decisions to clients and co-ordinating sub tasks of larger projects.

PROFESSIONAL REQUIREMENTS

Must have Master’s Degree in Computer Science, Information Technology or Information Security; Five (5) years of experience in such positions as Network Engineer, Information Security Administrator and/or Network Security Analyst. Must have certificate in IS training.

PERSONAL REQUIREMENTS

-Willing to work in a flexible team

-Reliability

-Independent and thoughtful

-Pleasant communication skills

WE OFFER

We take your career seriously and offer the possibility to grow with us in a highly qualified, internationally experienced team. Our work environment is harmonic and team oriented, and at the same time challenging and interesting. We always look to achieve best results, and

15:25 [Job][New]

Applications are invited for one PhD position in the Security Group at the Computer Laboratory to work with Dr Steven Murdoch. Funding for this position is provided by the Engineering and Physical Sciences Research Council (EPSRC) in collaboration with the Royal Society.

The successful candidate will undertake research on methods to analyse the security of anonymous communication systems and privacy enhancing technologies. This broad research topic falls within an EPSRC priority area and provides considerable scope for the PhD candidate to find his or her own research direction.

Candidates should possess, or who will shortly obtain, at least an upper 2nd class honours degree in computer science, software engineering or a related discipline, and ideally, a Masters degree in a computer-science related field. Strong mathematical and programming skills, along with a keen interest in privacy and anonymous communications, are essential. A good understanding of networking and operating systems is highly desirable.

Funding (covering approved fees and living expenses for one person) is available for 3 years, and the successful candidate must be able to start on 30 September 2013. Candidates should be UK or EU citizens, or have appropriate permissions to work in the UK.