*21:17* [Pub][ePrint]
Official Arbitration and its Application to Secure Cloud Storage, by Alptekin Küpçü
Many cryptographic protocols exist that enable two parties to exchange items (e.g., e-commerce) or agree on something (e.g., contract-signing). In such settings, disputes may arise. Official arbitration refers to the process of resolving disputes between two (or more) parties by a trusted and authorized Judge, based on evidence provided. As an example, consider the secure cloud storage scenario where there needs to be an official arbitration process between the client and the server in case of data loss or corruption. Without such a mechanism that can be officially used by the Judge in the court, the barrier on the enterprise adoption of such systems is high.In this paper we first formally define official arbitration, and then provide several general purpose official arbitration protocols. Later, we focus on secure cloud storage, and provide efficient official arbitration schemes that can be used on top of any secure cloud storage scheme. We furthermore present a completely automated system where the Judge can just be a computer instead of a human being. All our constructions have security proofs, and we conclude with performance measurements showing that our overhead for official arbitration is roughly 2 ms and 80 bytes for each update on the stored data.

*21:17* [Pub][ePrint]
Cyptanalysis CDHP , BDHP and Tate pairing under certain conditions The Tate pairing is less secure than Weil, by Rkia Aouinatou (1) Mostafa Belkasmi (2)
This work fall within the cadre of Cryptanalysis. Because, undercertain condition, we would give a fairly simple method to solve

the CDHP (the Problem Computational of Diffie and Hellman) and

others problems associated to it. Since, solving this problem, will help

us to provide a solution to the BDH (Problem Bilinear of Diffie and

Hellman). The CDHP and BDHP are the heart of many cryptosystems

in the point of view security, so solving it may be a threat to this

cryptosystem\'s. To elucidate this, we use a concept of geometry

algebraic named Tate Pairing.

This work is purely theoretical, we give firstly an overview on the

idea and we illustrate it by an examples to see its efficiency.

*21:17* [Pub][ePrint]
Concurrent Zero Knowledge in the Bounded Player Model, by Abhishek Jain, Rafail Ostrovsky, Silas Richelson, Ivan Visconti
In this paper we put forward the Bounded Player Model for secure computation. In this new model, the number of players that will ever be involved in secure computations is bounded, but the number of computations has no a-priori bound. Indeed, while the number of devices and people on this planet can be realistically estimated and bounded, the number of computations these devices will run can not be realistically bounded.We stress that in the Bounded Player model, in addition to no apriori bound on the number of sessions, there is no synchronization barrier, no trusted party, and simulation must be performed in polynomial time.

In this setting, we achieve concurrent Zero Knowledge (cZK) with sub-logarithmic round complexity.

Our security proof is (necessarily) non-black-box, our simulator is straight-line and works as long as the number of rounds is $\\omega(1)$.

We further show that unlike previously studied relaxations of the standard model (e.g., timing assumptions, super-polynomial simulation), concurrent-secure computation is impossible to achieve in the Bounded Player model. This gives evidence that our model is closer to the standard model than previously studied models, and we believe might have additional applications.

*21:17* [Pub][ePrint]
Publicly Verifiable Delegation of Large Polynomials and Matrix Computations, with Applications, by Dario Fiore and Rosario Gennaro
Outsourced computations (where a client requests a server to perform some computation on its behalf) are becoming increasingly important due to the rise of Cloud Computing and the proliferation of mobile devices. Since cloud providers may not be trusted, a crucial problem is the verification of the integrity and correctness of such computation, possibly in a {\\em public} way, i.e., the result of a computation can be verified by any third party, and requires no secret key -- akin to a digital signature on a message.

We present new protocols for publicly verifiable secure outsourcing of

{\\em Evaluation of High Degree Polynomials} and {\\em Matrix Multiplication}. Compared to previously

proposed solutions, ours improve in efficiency and offer security in a stronger model.

The paper also discusses several practical applications of our protocols.

*21:17* [Pub][ePrint]
Some properties of q-ary functions based on spectral analysis, by Deep Singh and Maheshanand Bhaintwal
In this paper, we generalize some existing results on Booleanfunctions to the $q$-ary functions defined over $\\BBZ_q$, where

$q\\geq 2$ is an integer, and obtain some new characterization of

$q$-ary functions based on spectral analysis. We provide a

relationship between Walsh-Hadamard spectra of two $p$-ary functions

$f$ and $g$ (for $p$ a prime) and their derivative $D_{f, g}$. We

provide a relationship between the Walsh-Hadamard spectra and the

decompositions of any two $p$-ary functions. Further, we investigate

a relationship between the Walsh-Hadamard spectra and the

autocorrelation of any two $q$-ary functions.

*21:17* [Pub][ePrint]
Efficient UC-Secure Authenticated Key-Exchange for Algebraic Languages, by Olivier Blazy and Céline Chevalier and David Pointcheval and Damien Vergnaud
Authenticated Key Exchange (AKE) protocols enable two parties toestablish a shared, cryptographically strong key over an insecure network using various authentication means, such as cryptographic keys, short (i.e. low-entropy) secret keys or credentials. In this paper, we provide a general framework that encompasses several previous AKE primitives such as Password-Authenticated Key Exchange or Secret Handshakes. We call it LAKE for Language-Authenticated Key Exchange.

We first model this general primitive in the Universal Composability (UC) setting. Thereafter, we show that the Gennaro-Lindell approach can efficiently address this goal. But we need smooth projective hash functions on new languages, whose efficient implementations are of independent interest. We indeed provide such hash functions for languages defined by combinations of linear pairing product equations.

Combined with an efficient commitment scheme, derived from the highly-efficient UC-secure Lindell\'s commitment, we obtain a very practical realization of Secret Handshakes, but also Credential-Authenticated Key Exchange protocols.

All the protocols are UC-secure, in the standard model with a common reference string, under the classical Decisional Linear assumption.