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2013-06-25
18:17 [Pub][ePrint] Order-Preserving Encryption Secure Beyond One-Wayness, by Tal Malkin and Isamu Teranishi and Moti Yung

  Semantic-security of individual bits under a ciphertext are fundamental notion in modern cryptography. In this work we present the first results about this fundamental problem for Order-Preserving Encryption (OPE): ``what plaintext information can be semantically hidden by OPE encryptions?\'\' While OPE has gained much attention in recent years due to its usefulness in secure databases, any partial-plaintext indistinguishability (semantic security) result for it was open. Here, we propose a new indistinguishability-based security notion for OPE, which can ensure \\emph{secrecy of lower bits of a plaintext} (under essentially a random ciphertext probing setting). We then propose a new scheme satisfying this security notion (while earlier schemes do not satisfy it!). We note that the known security notions tell us nothing about the above partial- plaintext indistinguishability because they are limited to being one-way-based. In addition, we show that our security notion with specific parameters implies the known security notion called WOW, and further, our scheme achieves WOW with better parameters than earlier schemes.



18:17 [Pub][ePrint] Plug-and-Play IP Security: Anonymity Infrastructure Instead of PKI, by Yossi Gilad and Amir Herzberg

  We present the Plug-and-Play IP Security (PnP-IPsec) protocol. PnP-IPsec automatically establishes IPsec security associations between gateways, avoiding the need for manual administration and coordination between gateways, and the dependency on IPsec public key certificates - the two problems which are widely believed to have limited the use of IPsec mostly to intra-organization communication.

PnP-IPsec builds on Self-validated Public Data Distribution (SvPDD), a protocol that we present to establish secure connections between remote peers/networks, without depending on pre-distributed keys or certification infrastructure. Instead, SvPDD uses available anonymous communication infrastructures such as Tor, which we show to allow detection of MitM attacker interfering with communication. SvPDD may also be used in other scenarios lacking secure public key distribution, such as the initial connection to an SSH server.

We provide an open-source implementation of PnP-IPsec and SvPDD, and show that the resulting system is practical and secure.



18:17 [Pub][ePrint] Security Analysis of Lightweight Authentication Protocol from WISTP 2013, by Wang Shao-Hui, Xiao Fu, Chen Dan-wei, Wang Ru-chuan

  One of the key problems in Radio Frequency Identification (RFID) is security and privacy. Many RFID authentication protocols have been proposed to preserve security and privacy of the system. Nevertheless, most of these protocols are analyzed and it is shown that they can not provide security against some RFID attacks. In WISTP 2013, a new lightweight authentication protocol using AES S-box and some special function is presented. The new protocol has a good implementation in resource constrained tags. In this paper, we give the security analysis on this new authentication protocol. After impersonating the valid reader to query the tag and collecting the responses, we can deduce all the secrets shared between the reader and tag through analyzing the messages. The attack utilizes the structure of the invertible function and the property of the special function introduced in the new protocol.



18:17 [Pub][ePrint] Moduar Form Aprroach to Solving Lattice Problems, by Yuan Tian, Xueyong Zhu, Rongxin Sun

  We construct new randomized algorithms to find the exact solution to the shortest and closest vector problems (SVP and CVP) in Euclidean norm (l2) for the integral lattice. Not only the minimal norm of non-zero lattice vectors in SVP and the minimal distance in CVP, but also how many lattice vectors reach those minimums can be simultaneously computed by the algorithms. Our approach is based on some special properties of the generating function of lattice vectors\' (l2-)norms, the lattice-associated theta function, which is used in prior works mainly for hardness analysis on lattice problems but rarely for computational purposes. Such function\'s modular properties are exploited to develop our SVP and CVP solvers. In computational complexity perspective and take our SVP solver as an example, for the integral lattice family {Λn} of dimension dimΛn=n and level h=l(Λn) (the minimal positive integer such that the dual lattice Λn* scaled by h1/2 is integral) polynomial in n, the case frequently occurring in applications, this algorithm can find the minimal l2-norm of non-zero lattice vectors and the number of such shortest vectors in Λn with success probability 1-ε in asymptotic space complexity of polynomial in n and asymptotic time complexity of nO(n)log(1/ε). The only contribution to the algorithm\'s exponential time complexity nO(n)log(1/ε) comes from independently repeating a randomized lattice vector sampler nO(n)log(1/ε) times. All the rest of operations contribute to the algorithm\'s time-complexity only with an additive polynomial in n. Similar situations occur when solving the exact CVP by our algorithm. In other words, our solvers can be easily parallelized to be polynomial in time complexity. In addition, a variant of our CVP solver can solve the closest vector problem with preprocessing (CVPP) in polynomial time and nO(n)log(1/ε) space complexity.



18:17 [Pub][ePrint] Policy-Based Signatures, by Mihir Bellare and Georg Fuchsbauer

  We introduce signatures where signers can only sign messages that conform to some policy, yet privacy of the policy is maintained. We provide definitions and show that policy-based signatures provide a framework which yields a unified view of many other existing types of signatures that now appear as special cases. We also show how still other primitives are easily realized using policy-based signatures as a building block. We provide generic constructions of policy-based signatures and then show how to achieve them efficiently.



18:17 [Pub][ePrint] A novel certificateless deniable authentication protocol, by Chunhua Jin, Chunxiang Xu, Xiaojun Zhang, Qianna Xie, Fagen Li

  Deniable authenticated protocol is a new and attractive protocol compared to the traditional authentication protocol. It allows the appointed receiver to identify the source of a given message, but not to prove the identity of the sender to a third party even if the appointed receiver is willing to reveal its private key. In this paper, we first define a security model for certificateless deniable authentication protocols. Then we propose a non-interactive certificateless deniable authentication protocol, by combining deniable authentication protocol with certificateless cryptography. In addition, we prove its security in the random oracle model.



18:17 [Pub][ePrint] Short collision search in arbitrary SL2 homomorphic hash functions, by Ciaran Mullan and Boaz Tsaban

  We study homomorphic hash functions into SL2(q), the 2x2 matrices with determinant 1 over the

field with q elements.

Modulo a well supported number theoretic hypothesis, which holds in particular for all concrete

homomorphisms proposed thus far, we prove that

a random homomorphism is at least as secure as any concrete homomorphism.

For a family of homomorphisms containing several concrete proposals in the literature,

we prove that collisions of length O(log q) can be found in running time O(sqrt q).

For general homomorphisms we offer an algorithm that, heuristically and according to experiments,

in running time O(sqrt q) finds collisions of length O(log q) for q even, and length O(log^2 q/loglog q) for arbitrary q.

For any conceivable practical scenario, our algorithms are substantially faster than all earlier algorithms

and produce much shorter collisions.



18:17 [Pub][ePrint] Computational Fuzzy Extractors, by Benjamin Fuller and Xianrui Meng and Leonid Reyzin

  Fuzzy extractors derive strong keys from noisy sources. Their security is defined information- theoretically, which limits the length of the derived key, sometimes making it too short to be useful. We ask whether it is possible to obtain longer keys by considering computational security, and show the following.

-Negative Result: Noise tolerance in fuzzy extractors is usually achieved using an information reconciliation component called a \"secure sketch.\" The security of this component, which directly affects the length of the resulting key, is subject to lower bounds from coding theory. We show that, even when defined computationally, secure sketches are still subject to lower bounds from coding theory. Specifically, we consider two computational relaxations of the information-theoretic security requirement of secure sketches, using conditional HILL entropy and unpredictability entropy. For both cases we show that computational secure sketches cannot outperform the best information-theoretic secure sketches in the case of high-entropy Hamming metric sources.

-Positive Result: We show that the negative result can be overcome by analyzing computational fuzzy extractors directly. Namely, we show how to build a computational fuzzy extractor whose output key length equals the entropy of the source (this is impossible in the information-theoretic setting). Our construction is based on the hardness of the Learning with Errors (LWE) problem, and is secure when the noisy source is uniform or symbol-fixing (that is, each dimension is either uniform or fixed). As part of the security proof, we show a result of independent interest, namely that the decision version of LWE is secure even when a small number of dimensions has no error.



18:17 [Pub][ePrint] The Improved Cube Attack on Grain-v1, by Yongjuan Wang and Liren Ding and Wenbao Han and Xiangyu Wang

  The crucial problem of cube attack is the selection of cube set, which also being the most time-consuming process. This paper designs a new search algorithm which generates several linear equations through one cube set and applies cube attack to simplified version of Grain-v1algorithem. Our attack directly recovers 14 bits of the secret key when the initialization rounds in Grain-v1is 75 and finds 5 linear expressions about another 28 bits of the key.



18:17 [Pub][ePrint] Unconditional Tightness Bounds for Generic Reductions: The Exact Security of Schnorr Signatures, Revisited, by Nils Fleischhacker and Tibor Jager and Dominique Schröder

  A long line of research investigates the existence of tight security reductions for the Schnorr signature scheme. Most of these works presented lower tightness bounds, most recently Seurin (Eurocrypt 2012) showed that under certain assumptions the non-tight security proof for Schnorr signatures by Pointcheval and Stern (Eurocrypt 1996) is essentially optimal. All previous works in this direction share the same restrictions: The results hold only under the interactive one-more discrete logarithm assumption, they only consider algebraic reductions, and they only rule out tight reductions from the (one-more) discrete logarithm problem. The existence of a tight reduction from weaker computational problems, like CDH or DDH, remained open.

In this paper we introduce a new meta-reduction technique, which allows to prove lower bounds for the large and very natural class of generic reductions. A generic reduction is independent of a particular representation of group elements. Most reductions in state-of-the-art security proofs have this desirable property. This new approach allows to show unconditionally that there is no tight generic reduction from any natural computational problem \\Pi defined over algebraic groups (including even interactive problems) to breaking Schnorr signatures, unless solving \\Pi is easy.



16:43 [Job][New] Assistant Professor (tenure track), Technische Universiteit Eindhoven

  We are looking for a candidate who meets the following requirements:

  • A PhD degree in Mathematics or Computer Science;

  • Research experience in coding theory or coding theory;

  • Outstanding research achievements and promise for the future;

  • Excellent track record of international publications in leading journals and high-ranked conferences;

  • High potential for the acquisition of external research funds;

  • Readiness to supervise PhD projects;

  • Teaching experience and good teaching skills;

  • Good English speaking and writing skills, and a willingness to learn Dutch (all Master\\\'s and some Bachelor courses are given in English);

  • Basic Teaching Qualification (BKO): if the candidate in question is not in possession of a BKO certificate, he or she is required to meet this requirement within a maximum period of three years.

    The Department of Mathematics and Computer Science of the Eindhoven University of Technology (TU/e) has a vacancy for a Tenure Track Assistant Professor position for five years in the Coding and Crypto group (section Discrete Mathematics, DM).

    The tenure-track nature of the position will be as follows. The successful candidate will first be appointed for a fixed period of five years. Before the start of the contract, the department and the candidate negotiate a list of conditions for successful conversion. If the candidate meets these conditions at the end of the five years, the position becomes permanent; if not, the temporary position is not continued.