International Association for Cryptologic Research

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2012-09-06
18:17 [Pub][ePrint]

In this paper we provide a corrected and generalized version of the scheme presented at SOFSEM\'2012 in our paper Optimizing Segment Based Document Protection\'\' (SOFSEM 2012: Theory and Practice of Computer Science, LNCS 7147, pp. 566-575).

We develop techniques for protecting documents with restricted access rights. In these documents so called \\emph{segments} are encrypted. Different segments may be encrypted with different keys so that different user may be given different \\emph{access rights}. Hierarchy of access rights is represented by means of a directed acyclic \\emph{access graph}. The segments are encrypted with keys - where each key corresponds to one node in the access graph. The main feature of the access graph is that if there is an arch $\\overrightarrow{AB}$ in the graph, then all segments labelled with $B$ can be decrypted with the key corresponding to node $A$.

We show how to minimize the space overhead necessary for auxiliary keying information stored in the document. We provide an algorithm based on node disjoint paths in the access graph and key derivation based on one-way functions. Our current solution, based on maximal weighted matchings, provides an optimal solution for creating subdocuments, in case when frequency of creating each subdocument is known.

18:17 [Pub][ePrint]

We construct a functional encryption scheme secure against an a priori bounded polynomial number of collusions for the class of all polynomial-size circuits. Our constructions require only semantically secure public-key encryption schemes and pseudo-random generators computable by small-depth circuits (known to be implied by

most concrete intractability assumptions). For certain special cases such as predicate encryption schemes with public index, the construction requires only semantically secure encryption schemes, which is clearly the minimal necessary assumption.

Our constructions rely heavily on techniques from secure multiparty computation and randomized encodings. All our constructions are secure under a strong, adaptive simulation-based definition of functional encryption.

18:17 [Pub][ePrint]

We investigate False Positive (FP) accusation probabilities for

q-ary Tardos codes in the Restricted Digit Model.

We employ a computation method recently introduced by us,

to which we refer as Convolution and Series Expansion (CSE).

We present a comparison of several collusion attacks on q-ary codes: majority voting, minority voting, Interleaving, $\\tilde\\mu$-minimizing and Random Symbol (the q-ary equivalent of the Coin Flip strategy).

The comparison is made by looking at the FP rate at approximately fixed False Negative rate.

In nearly all cases we find that the strongest attack is either

minority voting or $\\tilde\\mu$-minimizing, depending on the exact setting of parameters such as alphabet size, code length, and coalition size.

Furthermore, we present results on the convergence speed of the CSE method, and we show how FP rate computations for the Random Symbol strategy can be sped up by a pre-computation step.

18:17 [Pub][ePrint]

It is well-known that one-way permutations (and even one-to-one one-way functions) imply the existence of non-interactive commitments. Furthermore the construction is black-box (i.e., the underlying one-way function is used as an oracle to implement the commitment scheme, and an adversary attacking the commitment scheme is used as an oracle in the proof of security).

We rule out the possibility of black-box constructions of non interactive commitments from general (possibly not one-to-one) one-way functions. As far as we know, this is the first result showing a natural cryptographic task that can be achieved in a black-box way from one-way permutations but not from one-way functions.

We next extend our black-box separation to constructions of non-interactive commitments from a stronger notion of one-way functions, which we refer to as \\emph{hitting} one-way functions. Perhaps surprisingly, Barak, Ong, and Vadhan (Siam JoC \'07) showed that there does exist a non-black-box construction of non-interactive commitments from hitting one-way functions. As far as we know, this is the first result to establish a separation\'\' between the power of black-box and non-black-box use of a primitive to implement a natural cryptographic task.

We finally show that unless the complexity class NP has program checkers, the above separations extend also to non-interactive instance-based commitments, and 3-message public-coin honest-verifier zero-knowledge protocols with O(log n)-bit verifier messages. The well-known classical zero-knowledge proof for NP fall into this category.

12:51 [Job][New]

The position is located at the Department of Information and Computer Science (http://ics.aalto.fi/ ), and is open to outstanding individuals who hold a doctorate and have excellent potential for a successful scientific career. Research fields compatible with the call are algorithms, logic and complexity. Within these fields the areas of cryptology, combinatorial algorithms, computational logic, and distributed computing are currently represented at the Department.

Aalto University (http://www.aalto.fi/en/) is a new university created in 2010 from the merger of the Helsinki University of Technology TKK, Helsinki School of Economics and the University of Art and Design Helsinki. The University’s cornerstones are its strengths in education and research, with 20,000 basic degree and graduate students, and a staff of 5 000 of whom 350 are professors.

12:51 [Job][New]

Resistance against side channel and fault attacks is a fast evolving research field.

We propose, in collaboration with an industrial partner, a funded PhD thesis on these topics. The student will be based in the Paris area and will benefit from an academic R&D environment in which several PhD students work already.

The candidate should have good knowledge instrumentation and programming and a creative mindset. Good mastery of mathematics in general and of signal processing in particular is a plus.

The successful candidate should have a Master’s degree in computer science, metrology or a related field. Knowledge of cryptography and hardware security is an asset. Knowledge of French is not required.

12:51 [Job][New]

Biometric authentication (1 to 1 matching) and identification (1 to many) are becoming increasingly popular. To speed-up these operations, we wish to explore the design of dedicated hardware accelerators for fingerprint matching. We propose, in collaboration with an industrial partner, a funded PhD thesis on this topic. The student will be based in the south of France (Aix en Provence area) and will benefit from an academic R&D environment in which several PhD students work already.

The candidate should have good knowledge of HDL design and a creative mindset. Good mastery of mathematics in general and of signal processing in particular is a plus.

The successful candidate should have a Master’s degree in hardware design or in microelectronics or a related field. Knowledge of cryptography and hardware security is an asset. Knowledge of French is not required.

12:50 [Job][New]

Very frequently open source microprocessors are used to derive secure versions. The hardening of such devices against attacks can be done either invasively (by physically changing the device) or non-invasively (by adding circuits around the device and software inside it). We propose, in collaboration with an industrial partner, a funded PhD thesis on this topic. The student will be based in the Paris area and will benefit from an R&D environment in which several PhD students work already.

The candidate should have good knowledge of HDL design and a creative mindset.

The successful candidate should have a Master’s degree in hardware design or in microelectronics or a related field. Knowledge of cryptography and hardware security is an asset. Knowledge of French is not required.

12:50 [Job][New]

The Computer Science Department at University College London has an open postdoctoral research position under the supervision of Dr Jens Groth. The Research Associate is funded by an ERC Starting Grant on Efficient Cryptographic Arguments and Proofs with a flexible start date and a duration of up to 3 years.

Candidates must have a PhD with a strong publication record in cryptography or theoretical computer science. Research experience in zero-knowledge proofs, probabilistically checkable proofs or lattice-based cryptography will be considered a plus.

University College London is one of Europe\'s highest ranked universities and has recently been recognized by the EPSRC and GCHQ as one of UK\'s Academic Centres of Excellence in Cyber Security Research. The Computer Science Department is one of the largest in the UK and is located at UCL\'s main campus in the centre of London.

09:17 [Pub][JoC]

Abstract  In a proof-of-retrievability system, a data storage center must prove to a verifier that he is actually storing all of a client’s data. The central challenge is to build systems that are both efficient and provably secure—that is, it should be possible to extract the client’s data from any prover that passes a verification check. In this paper, we give the first proof-of-retrievability schemes with full proofs of security against arbitrary adversaries in the strongest model, that of Juels and Kaliski. Our first scheme, built from BLS signatures and secure in the random oracle model, features a proof-of-retrievability protocol in which the client’s query and server’s response are both extremely short. This scheme allows public verifiability: anyone can act as a verifier, not just the file owner. Our second scheme, which builds on pseudorandom functions (PRFs) and is secure in the standard model, allows only private verification. It features a proof-of-retrievability protocol with an even shorter server’s response than our first scheme, but the client’s query is long. Both schemes rely on homomorphic properties to aggregate a proof into one small authenticator value.

• Content Type Journal Article
• Pages 1-42
• DOI 10.1007/s00145-012-9129-2
• Authors

• Hovav Shacham, University of California, San Diego, La Jolla, CA, USA
• Brent Waters, University of Texas at Austin, Austin, TX, USA

• Journal Journal of Cryptology
• Online ISSN 1432-1378
• Print ISSN 0933-2790

From: Sun, 02 Sep 2012 03:14:04 GMT

08:12 [Job][New]

The Cryptographic Algorithms (CA) group in the Computer Science Department of Saarland University is currently offering a PhD position. The CA group is part of the newly established Center for IT-Security, Privacy and Accountability (CISPA). CISPA actively supports collaborations with other research centers worldwide, and offers young researchers an ideal working environment in every respect. The close connection of the CISPA to the department of computer science, the Max-Planck-Institute (MPI) for Informatics, the MPI for Software Systems, the German Research Center for Artificial Intelligence (DFKI), the Cluster of Excellence on Multimodal Computing and Interaction (MMCI), the Saarbrücken Graduate School of Computer Science and the Intel Visual Computing Institute (IVCI) is crucial for the success of the location. All of these institutes are in close proximity on the campus.

The CA group conducts research in various aspects of cryptography. Topics of particular interest include, but are not limited to design of cryptographic algorithms and protocols as well as foundational research.

Applicants are required to have completed (or be close to completing) a Bachelor, Master, or Diplom with outstanding grades in Computer Science, Mathematics, or closely related areas. Additional knowledge in related disciplines such as, e.g., complexity theory is welcome. We stress that PhD applications immediately after the Bachelor degree are possible and welcome, as part of the Saarbruecken Graduate CS School. The working and teaching language is English.

Please send your application to Dominique Schroeder via e-mail. Applications should contain a CV, copies of transcripts and certificates, and (if possible) names of references. Applications will be accepted until the position has been filled.