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2013-05-28
05:22 [Pub][ePrint] The Potential of Individualized Trusted Root Stores: Minimizing the Attack Surface in the Light of CA Failures, by Johannes Braun and Gregor Rynkowski

  The security of most Internet applications relies on underlying public key infrastructures (PKIs) and thus on an ecosystem of certification authorities (CAs). The pool of PKIs responsible for the issuance and the maintenance of SSL certificates, called the Web PKI, has grown extremely large and complex. Herein, each CA is a single point of failure for the security, leading to an attack surface, the size of which is hardly assessable.

This paper approaches the issue if and how the attack surface can be reduced in order to reduce the risk of relying on a malicious certificate. In particular we consider the individualization of the set of trusted CAs. We present a tool called Rootopia, which allows to assess the respective part of the Web PKI relevant for a user.

Our analysis of browser histories of 22 Internet users reveals, that the major part of the PKI is completely irrelevant to a single user. The attack surface can be reduced by more than 90%, which shows the potential of the individualization of the set of trusted CAs. Furthermore, all the relevant CAs reside within a small set of countries. Our findings confirm, that we unnecessarily trust in a

huge number of CAs, exposing ourselves to unnecessary risks.



05:22 [Pub][ePrint] Towards a Practical Cryptographic Voting Scheme Based on Malleable Proofs, by David Bernhard and Stephan Neumann and Melanie Volkamer

  Mixnets are one of the main approaches to deploy secret and verifiable electronic elections.

General-purpose verifiable mixnets however suffer from the drawback that the amount of data to be verified by observers increases linearly with the number of involved mix nodes, the number of decryptors, and the number of voters. Chase et al. proposed a verifiable mixnet at Eurocrypt 2012 based on so-called \\emph{malleable proofs} - proofs that do not increase with the number of mix nodes. In work published at PKC 2013, the same authors adapted malleable proofs to verifiable distributed decryption, resulting in a cryptographic voting scheme. As a result, the amount of data to be verified only increases linearly with the number of voters.

However, their scheme leaves several questions open which we address in this paper:

As a first contribution, we adapt a multi-party computation protocol to build a distributed key generation protocol for the encryption scheme underlying their voting scheme. As a second contribution, we decompress their abstract scheme description, identify elementary operations, and count the number of such operations required for mixing and verification. Based on timings for elementary operations, we extrapolate the running times of the mixing and verification processes, allowing us to assess the feasibility of their scheme. For the German case, we conclude that the replacement of postal voting by cryptographic voting based on malleable proofs is feasible on an electoral district level.



05:22 [Pub][ePrint] ESPOON: Enforcing Encrypted Security Policies in Outsourced Environments, by Muhammad Rizwan Asghar and Mihaela Ion and Giovanni Russello and Bruno Crispo

  The enforcement of security policies in outsourced environments is still an open challenge for policy-based systems. On the one hand, taking the appropriate security decision requires access to the policies. However, if such access is allowed in an untrusted environment then confidential information might be leaked by the policies. Current solutions are based on cryptographic operations that embed security policies with the security mechanism. Therefore, the enforcement of such policies is performed by allowing the authorised parties to access the appropriate keys. We believe that such solutions are far too rigid because they strictly intertwine authorisation policies with the enforcing mechanism.

In this paper, we want to address the issue of enforcing security policies in an untrusted environment while protecting the policy confidentiality. Our solution ESPOON is aiming at providing a clear separation between security policies and the enforcement mechanism. However, the enforcement mechanism should learn as less as possible about both the policies and the requester attributes.



05:22 [Pub][ePrint] A Frequency Leakage Model and its application to CPA and DPA, by S. Tiran and S. Ordas and Y. Teglia and M. Agoyan and P. Maurine

  This paper introduces a leakage model in the frequency domain to

enhance the efficiency of Side Channel Attacks of CMOS circuits. While usual techniques are focused on noise removal around clock harmonics, we show that the actual leakage is not necessary located in those expected bandwidths as experimentally observed by E. Mateos and C.H. Gebotys in 2010. We start by building a theoretical modeling of power consumption and electromagnetic emanations before deriving from it a criterion to guide standard attacks. This criterion is then validated on real experiments, both on FPGA and ASIC, that show an impressive increase of the yield of SCA.



05:22 [Pub][ePrint] Pinocchio: Nearly Practical Verifiable Computation, by Bryan Parno and Craig Gentry and Jon Howell and Mariana Raykova

  To instill greater confidence in computations outsourced to the cloud, clients should be able to verify the correctness of the results returned. To this end, we introduce Pinocchio, a built system for efficiently verifying general computations while relying only on cryptographic assumptions. With Pinocchio, the client creates a public evaluation key to describe her computation; this setup is proportional to evaluating the computation once. The worker then evaluates the computation on a particular input and uses the evaluation key to produce a proof of correctness. The proof is only 288 bytes, regardless of the computation performed or the size of the inputs and outputs. Anyone can use a public verification key to check the proof. Pinocchio achieves strong asymptotic efficiency by refining the Quadratic Arithmetic Programs of Gennaro, Gentry, Parno, and Raykova (EuroCrypt 2013).

Crucially, our evaluation on seven applications demonstrates that Pinocchio is efficient in practice too. Pinocchio\'s verification time is typically 10ms: 5-7 orders of magnitude less than previous work; indeed Pinocchio is the first general-purpose system to demonstrate per-instance verification cheaper than native execution (for some apps). Pinocchio also reduces the worker\'s proof effort by an additional 19-60x. As an additional feature, Pinocchio generalizes to zero-knowledge proofs at a negligible cost over the base protocol. Finally, to aid development, Pinocchio provides an end-to-end toolchain that compiles a subset of C into programs that implement the verifiable computation protocol.



05:22 [Pub][ePrint] Path ORAM: An Extremely Simple Oblivious RAM Protocol, by Emil Stefanov and Marten van Dijk and Elaine Shi and Christopher Fletcher and Ling Ren and Xiangyao Yu and Srinivas Devadas

  We present Path ORAM, an extremely simple Oblivious RAM protocol with a small amount of client storage. Partly due to its simplicity, Path ORAM is the most practical ORAM scheme known to date. We formally prove that Path ORAM requires O(log^2 N / k) bandwidth overhead for block size B = k * log N. For block sizes bigger than O(log^2 N) bits, Path ORAM is asymptotically better than the best known ORAM scheme with small client storage. Due to its practicality, Path ORAM has been adopted in the design of secure processors since its proposal.



05:22 [Pub][ePrint] Adapting Lyubashevsky\'s Signature Schemes to the Ring Signature Setting, by Carlos Aguilar-Melchor and Slim Bettaieb and Xavier Boyen and Laurent Fousse and Philippe Gaborit

  Basing signature schemes on strong lattice problems has been a long standing open issue. Today, two families of lattice-based signature schemes are known: the ones based on the hash-and-sign construction of Gentry et al.; and Lyubashevsky\'s schemes, which are based on the Fiat-Shamir framework.

In this paper we show for the first time how to adapt the schemes of Lyubashevsky to the ring signature setting. In particular we transform the scheme of ASIACRYPT 2009 into a ring signature scheme that provides strong properties of security under the random oracle model. Anonymity is ensured in the sense that signatures of different users are within negligible statistical distance even under full key exposure. In fact, the scheme satisfies a notion which is stronger than the classical full key exposure setting as even if the keypair of the signing user is adversarially chosen, the statistical distance between signatures of different users remains negligible.

Considering unforgeability, the best lattice-based ring signature schemes provide either unforgeability against arbitrary chosen subring attacks or insider corruption in log-sized rings. In this paper we present two variants of our scheme. In the basic one, unforgeability is ensured in those two settings. Increasing signature and key sizes by a factor k (typically 80 − 100), we provide a variant in which unforgeability is ensured against insider corruption attacks for arbitrary rings. The technique used is pretty general and can be adapted to other existing schemes.



05:22 [Pub][ePrint] Three Snakes in One Hole: A 67 Gbps Flexible Hardware for SOSEMANUK with Optional Serpent and SNOW 2.0 Modes, by Goutam Paul and Anupam Chattopadhyay

  With increasing usage of hardware accelerators in modern heterogeneous

System-on-Chips (SoCs), the distinction between hardware and software is no longer rigid. The domain of cryptography is no exception and efficient hardware design of so-called software ciphers are becoming increasingly popular. In this paper, for the first time we propose an efficient hardware accelerator design for SOSEMANUK, one of the finalists of the eSTREAM stream cipher competition in the software category. Since SOSEMANUK combines the design principles of the block cipher Serpent and the stream cipher SNOW 2.0, we make our design

flexible to accommodate the option for independent execution of Serpent and SNOW 2.0. In the process, we identify interesting design points and explore different levels of optimizations. We perform a detailed experimental evaluation of the performance figures of each design point and in each case our figures by far outperform the existing benchmarks. The best throughput achieved by the combined design is 67.84 Gbps for SOSEMANUK, 33.92 Gbps for SNOW 2.0 and 2.12 Gbps for Serpent. The throughput for SOSEMANUK by far outperforms all existing benchmarks on the eSTREAM candidates.



05:22 [Pub][ePrint] Function-Private Identity-Based Encryption: Hiding the Function in Functional Encryption, by Dan Boneh and Ananth Raghunathan and Gil Segev

  We put forward a new notion, function privacy, in identity-based encryption and, more generally, in functional encryption. Intuitively, our notion asks that decryption keys reveal essentially no information on their corresponding identities, beyond the absolute minimum necessary. This is motivated by the need for providing predicate privacy in public-key searchable encryption. Formalizing such a notion, however, is not straightforward as given a decryption key it is always possible to learn some information on its corresponding identity by testing whether it correctly decrypts ciphertexts that are encrypted for specific identities.

In light of such an inherent difficulty, any meaningful notion of function privacy must be based on the minimal assumption that, from the adversary\'s point of view, identities that correspond to its given decryption keys are sampled from somewhat unpredictable distributions. We show that this assumption is in fact sufficient for obtaining a strong and realistic notion of function privacy. Loosely speaking, our framework requires that a decryption key corresponding to an identity sampled from any sufficiently unpredictable distribution is indistinguishable from a decryption key corresponding to an independently and uniformly sampled identity.

Within our framework we develop an approach for designing function-private identity-based encryption schemes, leading to constructions that are based on standard assumptions in bilinear groups (DBDH, DLIN) and lattices (LWE). In addition to function privacy, our schemes are also anonymous, and thus yield the first public-key searchable encryption schemes that are provably keyword private: A search key sk_w enables to identify encryptions of an underlying keyword w, while not revealing any additional information about w beyond the minimum necessary, as long as the keyword w is sufficiently unpredictable.



05:22 [Pub][ePrint] A Secure Paper-Based Electronic Voting With No Encryption, by Asghar Tavakkoli, Reza Ebrahimi Atani

  Abstract: We present a paper-based voting method that attempts to achieve the privacy of voters and election universal verifiability and integrity with only paper ballots and without using any cryptography method. The voting procedure is easy and it needs only selecting the intention of voter over screen of an electronic device. The rest of the voting procedure will be carried out by the device. Voter gets a receipt that can be used to verify that his vote has been counted in final tally as he intended. However the receipt cannot help voter to reveal who he voted for. Also vote selling or coercion is not possible even with the voter\'s cooperation. The ballot in our voting method has two side, one positive and one negative. Ballots have been prepared for voting in prepackaged form (i.e. 5 ballots per package). Some bubbles of each ballot are prefilled in random way. Numbers of positive and negative filled bubbles are equal with each other and also for each candidate in a package. For example if every package has 30 filled bubbles and if there are three candidates, there would be 10 filled bubbles for each candidate in a package. As it is clear half of those are positive and the other half are negative. The procedure of OneBallot voting is as follows: Voter puts the ballot inside of an electronic device and then he chooses his candidate on the device screen. Then device print another ballot exact same as the original one by one difference; the device fills one positive bubble or unfills one negative bubbles for the selected candidate. First action can be done on the original ballot but the second one needs to print new ballot inevitably. Then device makes a copy from new ballot as voter\'s receipt and transfers original ballot to the ballot box. After election, there will be a copy from all of ballots in a public board (i.e. a website).



05:22 [Pub][ePrint] A Novel Proof on Weil Pairing, by Sutirtha Sanyal

  In this paper we will prove a basic property of weil pairing which helps in evaluating its value. We will show that the weil pairing value as

computed from the definition is equivalent with the ratio formula based on the miller function. We prove a novel theorem (Theorem 2) and use it

to establish the equivalence. We further validate our claims with actual random examples.