*06:58*[Job][New] Post-Doc,

*Ben-Gurion University of the Negev, Israel*

The research will be in the scopes of:

Securing and preserving private computation in the cloud.

Cyber security.

Distributed computing.

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The research will be in the scopes of:

Securing and preserving private computation in the cloud.

Cyber security.

Distributed computing.

Let $E$ be an elliptic curve over a finite field ${\\mathbb F}_q$ with a power of prime $q$, $r$ a prime dividing $\\#E({\\mathbb F}_q)$, and $k$ the smallest positive integer satisfying $r | \\Phi_k(p)$, called embedding degree. Then a bilinear map $t: E({\\mathbb F}_q)[r] \\times E({\\mathbb F}_{q^k})/rE({\\mathbb F}_{q^k}) \\rightarrow {\\mathbb F}_{q^k}^*$ is defined, called the Tate pairing. And the Ate pairing and other variants are obtained by reducing the domain for each argument and raising it to some power.

In this paper we consider the {\\em Fixed Argument Pairing Inversion (FAPI)} problem for the Tate pairing and its variants. In 2012, considering FAPI for the Ate$_i$ pairing, Kanayama and Okamoto formulated the {\\em Exponentiation Inversion (EI)} problem. However the definition gives a somewhat vague description of the hardness of EI. We point out that the described EI can be easily solved, and hence clarify the description so that the problem does contain the actual hardness connection with the prescribed domain for given pairings.

Next we show that inverting the Ate pairing (including other variants of the Tate pairing) defined on the smaller domain is neither easier nor harder than inverting the Tate pairing defined on the lager domain. This is very interesting because it is commonly believed that the structure of the Ate pairing is so simple and good (that is, the Miller length is short, the solution domain is small and has an algebraic structure induced from the Frobenius map) that it may leak some information, thus there would be a chance for attackers to find further approach to solve FAPI for the Ate pairing, differently from the Tate pairing.

In a digital signature scheme with message recovery, rather than transmitting the message $m$ and its signature $\\sigma$, a single enhanced signature $\\tau$ is transmitted. The verifier is able to recover $m$ from $\\tau$ and at the same time

verify its authenticity. The two most important parameters of such a scheme are its security and the overhead $|\\tau|-|m|$. A simple argument shows that for any scheme with ``$n$ bits security\" $|\\tau|-|m|\\ge n$, i.e., the overhead is at least the security. The best previous constructions required an overhead of $2n$. In this paper we show that the $n$ bit lower bound can basically be matched. Concretely, we propose a new simple RSA-based digital signature scheme that, for $n=80$ bits security in the random oracle model, has an overhead of $\\approx 90$ bits.

At the core of our security analysis is an almost tight upper bound for the expected number of edges of the densest ``small\'\' subgraph of a random Cayley graph, which may be of independent interest.

At NDSS 2012, Yan et al. analyzed the security of several challenge-response type user authentication protocols against passive observers, and proposed a generic counting based statistical attack to recover the secret of some counting based protocols given a number of observed authentication sessions. Roughly speaking, the attack is based on the fact that secret (pass) objects appear in challenges with a different probability from non-secret (decoy) objects when the responses are taken into account. Although they mentioned that a protocol susceptible to this attack should minimize this difference, they did not give details as to how this can be achieved barring a few suggestions.

In this paper, we attempt to fill this gap by generalizing the attack with a much more comprehensive theoretical analysis. Our treatment is more quantitative which enables us to describe a method to theoretically estimate a lower bound on the number of sessions a protocol can be safely used against the attack. Our results include 1) two proposed fixes to make counting protocols practically safe against the attack at the cost of usability, 2) the observation that the attack can be used on non-counting based protocols too as long as challenge generation is contrived, 3) and two main design principles for user authentication protocols which can be considered as extensions of the principles from Yan et al. This detailed theoretical treatment can be used as a guideline during the design of counting based protocols to determine their susceptibility to this attack. The Foxtail protocol, one of the protocols analyzed by Yan et al., is used as a representative to illustrate our theoretical and experimental results.

Image compression and image encryption are pivotal to proper storage and transmission of images over MANET. Simultaneous image compression and encryption aims at achieving enhanced bandwidth utilization and security at the same time. The Number Theory based Image Compression and Quasigroup Encryption (NTICQE) algorithm employs number theoretic paradigm - Chinese Remainder Theorem and Quasigroup Encryption, to solve congruencies and hence realize the twin ideals of compression and encryption simultaneously. Quasigroup encryptor that has very good data-scrambling properties and, therefore, it has potential uses in symmetric cryptography.

In their paper ``A Quasigroup Based Random Number Generator for Resource Constrained Environments\", the authors Matthew Battey and Abhishek Parakh propose the pseudo random number generator LOQG PRNG 256. We show several highly efficient attacks on LOQG PRNG 256.

Physically Unclonable Functions (PUFs) exploit the physical characteristics of silicon and provide an alternative to storing digital encryption keys in non-volatile memory. A PUF maps a unique set of digital inputs to a corresponding set of digital outputs. In this paper, the use of asynchronous logic and design techniques to implement PUFs is advocated for Asynchronous Physically Unclonable Functions (APUFs). A new method of using asynchronous rings to implement PUFs is described called ASYNCPUF which features inherent field programmability. It is both a novel and holistic PUF design compared to the existing state-of-the-art as it naturally addresses the two challenges facing PUFs to-date that prevent wide-spread adoption: robustness and entropy. Results of electrical simulation in a 90 nano-meter lithography process are presented and discussed.

2012-11-22

Abstract We provide a more general and, in our eyes, simpler variant of Prabhakaran, Rosen and Sahai’s (FOCS ’02, pp. 366–375, 2002) analysis of the concurrent zero-knowledge simulation technique of Kilian and Petrank (STOC ’01, pp. 560–569, 2001).

- Content Type Journal Article
- Pages 1-22
- DOI 10.1007/s00145-012-9137-2
- Authors
- Rafael Pass, Cornell University, Ithaca, NY 14853, USA
- Wei-Lung Dustin Tseng, Google Inc., 747 6th street, Kirkland, WA, USA
- Muthuramakrishnan Venkitasubramaniam, University of Rochester, 621 Computer Sciences Building, Rochester, NY 14627-0226, USA

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

2012-11-21

This article introduces a definition of privacy for Direct Anonymous Attestation schemes. The definition is expressed as an equivalence property suited to automated reasoning using ProVerif and the practicality of the definition is demonstrated by analysing the RSA-based Direct Anonymous Attestation protocol by Brickell, Camenisch & Chen. The analysis discovers a vulnerability in the RSA-based scheme which can be exploited by a passive adversary and, under weaker assumptions, corrupt administrators. A security fix is identified and the revised protocol is shown to satisfy our definition of privacy.

Data access control is an effective way to ensure the data security in the cloud. Due to data outsourcing and untrusted cloud servers, the data access control becomes a challenging issue in cloud storage systems.

Ciphertext-Policy Attribute-based Encryption (CP-ABE), as a promising technique for access control of encrypted data, is very suitable for access control in cloud storage systems due to its high efficiency and expressiveness.

However, the existing CP-ABE schemes cannot be directly applied to data access control for cloud storage systems because of the attribute revocation problem. In this paper, we consider the problem of attribute revocation in multi-authority cloud storage systems where the users\' attributes come from different domains each of which is managed by a different authority.

We propose TAAC (Temporal Attribute-based Access Control), an efficient data access control scheme for multi-authority cloud storage systems, where the authorities are independent from each other and no central authority is needed. TAAC can efficiently achieve temporal access control on attribute-level rather than on user-level. Moreover, different from the existing schemes with attribute revocation functionality, TAAC does not require re-encryption of any ciphertext when the attribute revocation happens, which means great improvement on the efficiency of attribute revocation. The analysis results show that TAAC is highly efficient, scalable, and flexible to applications in practice.

We consider the problem of constructing protocols for secure computation that achieve strong concurrent and composable notions of security in the plain model. Unfortunately UC-secure secure computation protocols are impossible in this setting, but the Angel-Based Composable Security notion offers a promising alternative. Until now, however, under standard (polynomial-time) assumptions, only protocols with polynomially many rounds were known to exist.

In this work, we give the first $\\tilde{O}(\\log n)$-round secure computation protocol in the plain model that achieves angel-based composable security in the concurrent setting, under standard assumptions. We do so by constructing the first $\\tilde{O}(\\log n)$-round CCA-secure commitment protocol. Our CCA-secure commitment protocol is secure based on the minimal assumption that one-way functions exist.

A central tool in obtaining our result is a new \\emph{robust concurrent extraction lemma} that we introduce and prove, based on the minimal assumptions that one-way functions exist. This robust concurrent extraction lemma shows how to build concurrent extraction procedures that work even in the context of an ``external\'\' protocol that cannot be rewound by the extractor. We believe this lemma can be used to simplify many existing works on concurrent security, and is of independent interest. In fact, our lemma when used in conjunction with the concurrent-simulation schedule of Pass and Venkitasubramaniam (TCC\'08), also yields a constant round construction based additionally on the existence of quasi-polynomial time (\\pqt) secure one-way functions.