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2015-07-18
15:17 [Pub][ePrint]

Mobile application spoofing is an attack where a malicious mobile application

mimics the visual appearance of another one. If such an attack is successful,

the integrity of what the user sees as well as the confidentiality of what she

inputs into the system can be violated by the adversary. A common example of

mobile application spoofing is a phishing attack where the adversary tricks the

user into revealing her password to a malicious application that resembles the

legitimate one.

In this work, we propose a novel approach for addressing mobile application

spoofing attacks by leveraging the visual similarity of application screens. We

use deception rate as a novel metric for measuring how many users would confuse

a spoofing application for the genuine one. We conducted a large-scale online

study where participants evaluated spoofing samples of popular mobile

applications. We used the study results to design and implement a prototype

spoofing detection system, tailored to the estimation of deception rate for

15:17 [Pub][ePrint]

Storage requirements for visual data have been increasing in recent years, following the emergence of many new highly interactive multimedia services and applications for both personal and corporate use. This has been a key driving factor for the adoption of cloud-based data outsourcing solutions. However, outsourcing data storage to the Cloud also leads to new challenges that must be carefully addressed, especially regarding privacy. In this paper we propose a secure framework for outsourced privacy-preserving storage and retrieval in large image repositories. Our proposal is based on IES-CBIR, a novel Image Encryption Scheme that displays Content-Based Image Retrieval properties. Our solution enables both encrypted storage and searching using CBIR queries while preserving privacy. We have built a prototype of the proposed framework, formally analyzed and proven its security properties, and experimentally evaluated its performance and precision. Our results show that IES-CBIR is provably secure, allows more efficient operations than existing proposals, both in terms of time and space complexity, and enables more reliable practical application scenarios.

15:17 [Pub][ePrint]

The aim of this work is to find large S-Boxes, typically operating on 8

bits, having both good cryptographic properties and a low implementation

cost. Such S-Boxes are suitable building-blocks in many lightweight

block ciphers since they may achieve a better security level than

designs based directly on smaller S-Boxes. We focus on S-Boxes

corresponding to three rounds of a balanced Feistel and of a balanced

MISTY structure, and generalize the recent results by Li and Wang on the

best differential uniformity and linearity offered by such a

construction. Most notably, we prove that Feistel networks supersede

MISTY networks for the construction of 8-bit permutations. Based on

these results, we also provide a particular instantiation of an 8-bit

permutation with better properties than the S-Boxes used in several

ciphers, including Robin, Fantomas or CRYPTON.

15:17 [Pub][ePrint]

It has long been known (Shoup and Gennaro 1998) that non-interactive proofs in the Random Oracle model that rely on rewinding extractors can be problematic.

Recent results by Seurin and Treger and Bernhard et al. formally confirmed such limitations for proofs derived from the Schnorr protocol via the Fiat-Shamir transform.

The limitations relate to the concept of adaptive proofs where an extractor needs to recover witnesses from proofs selected adaptively, as opposed to the standard setting where the extractor needs to work just for one proof.

Their main result is a separation between these two settings: under the one-more discrete log assumption, no efficient adaptive extractor can recover all witnesses from non-interactive Schnorr proofs (selected adaptively).

In this paper we generalize, strengthen and extend these results.

First we show that the above separation result holds for generic Sigma-protocols under the natural generalization of the one-more dlog assumption.

Next, we strengthen the theorem by weakening the hypothesis.

Our new assumption, which we call Sigma-one-wayness, says that a dishonest verifier in a single execution of an interactive Sigma protocol cannot recover the witness.

This assumption is incomparable to zero-knowledge, as we will explain.

The main result of this paper clarifies the relation between adaptive proofs of knowledge (with rewinding) and other existing notions.

Bernhard et al. introduced adaptive proofs as a new concept lying

between proofs of knowledge (PoKs, with a rewinding extractor) and

straight-line extractable proofs. They showed a separation between PoKs and

adaptive proofs but left open the question whether adaptive proofs are always

straight-line.

against the honest prover. This means that adaptive proofs are not a new class

of proofs after all but simply another way to describe proofs with

straight-line extractors.

Finally, we ask ourselves whether the result could be extended to a

reduction to one-wayness of the function concerned -- for Schnorr, this would

mean solving the discrete logarithm (DLOG) problem. Our answer is negative: if

there is any generic metareduction from adaptivity of Fiat-Shamir-Schnorr to

DLOG then there is also a meta-metareduction breaking DLOG directly.

15:17 [Pub][ePrint]

This paper offers a new version of the hHB protocol denoted Light-hHB. This proposal uses the same framework as hHB, that is a two stages protocol: the first one for the establishment of a session key between the reader and the tag and the second one similar to HB+. We also introduce in this paper a novel and lightweight key exchange protocol inspired by the BB84 protocol named the non-quantum key exchange protocol. With the use of a practical implementation of the latter protocol in the first stage of Light-hHB, the transmission cost is drastically reduced compared to the one of hHB, which is its main drawback. In the context of RFID tags, Light-hHB is significantly more practical than hHB and achieves the same security goals.

15:17 [Pub][ePrint]

In this paper, we first present a new class of code based public key cryptosystem(PKC) based on Reed-Solomon code over $\\mathbb{F}_{2^m}$, referred to as K(XVI)SE(1)PKC.

We then present a new class of quadratic multivariate PKC, K(XVI)SE(2)PKC, based on cyclic code over $\\mathbb{F}_2$.

We show that both K(XVI)SE(1)PKC and K(XVI)SE(2)PKC can be secure against the various linear transformation attacks such as Gr\\\"obner bases attack due to a non-linear structure introduced to the ciphertexts.

Namely, thanks to the non-linear transformation introduced in the construction of K(XVI)SE(1)PKC and K(XVI)SE(2)PKC the ciphertexts can be made very secure against the various sorts of linear transformation attacks such as Gr\\\"obner bases attack, although the degree of the multivariate polynomial is all degree 1.

A new scheme presented in this paper that transforms message variables in order to realize non-linear transformations, K(I)TS, would yield a brand-new technique in the field of both code based PKC and multivariate PKC, for much improving the security.

We shall show that the K(XVI)SE(1)PKC can be effectively constructed based on the Reed-Solomon code over $\\mathbb{F}_{2^8}$, extensively used in the present day storage systems

or the various digital transmission systems.

15:17 [Pub][ePrint]

We investigate new constructions of n-circular counterexamples with a focus on the case of n=2. We have a particular interest in what qualities a cryptosystem must have to be able to separate such circular security from IND-CPA or IND-CCA security. To start, we ask whether there is something special about the asymmetry in bilinear groups that is inherent in the works of ABBC10 and CGH12 or whether it is actually the bilinearity that matters. As a further question, we explore whether such counterexamples are derivable from other

assumptions such as the Learning with Errors (LWE) problem. If it were difficult to find such counterexamples, this might bolster are confidence in using 2-circular encryption as a method of bootstrapping Fully Homomorphic Encryption systems that are based on lattice assumptions.

The results of this paper broadly expand the class of assumptions under which we can build 2-circular counterexamples. We first show for any constant k >= 2 how to build counterexamples from a bilinear group under the decision k-linear assumption. Recall that the decision k-linear assumption becomes progressively weaker as k becomes larger. This means that we can instantiate counterexamples

from symmetric bilinear groups and shows that asymmetric groups do not have any inherently special property needed for this problem.

We then show how to create 2-circular counterexamples from the Learning with Errors problem. This extends the reach of these systems beyond bilinear groups and obfuscation.

2015-07-16
18:11 [Pub][ePrint]

We present here optimized implementations of the MAKWA password hashing

function on an AMD Radeon HD 7990 GPU, and compare its efficiency with an Intel

i7 4770K CPU for systematic dictionary attacks. We find that the GPU seems to

get more hashing done for a given budget, but not by a large amount (the GPU is less

than twice as efficient as the CPU). Raising the MAKWA modulus size to 4096 bits,

instead of the default 2048 bits, should restore the balance in favour of the CPU. We

also find that power consumption, not hardware retail price, is likely to become the

dominant factor for industrialized, long-term attacking efforts.

18:11 [Pub][ePrint]

Statistical analysis of attacks on symmetric ciphers often require assuming the normal behaviour of a test statistic.

Typically such an assumption is made in an asymptotic sense. In this work, we consider concrete versions of some important

normal approximations that have been made in the literature. To do this, we use the Berry-Ess\\\'{e}en theorem to derive

explicit bounds on the approximation errors. Analysing these error bounds in the cryptanalytic context throws up several

surprising results. One important implication is that this puts in doubt the applicability of the order statistics

based approach for analysing key recovery attacks on block ciphers. This approach has been earlier used to obtain several

results on the data complexities of (multiple) linear and differential cryptanalysis. The non-applicability of the order

statistics based approach puts a question mark on the data complexities obtained using this approach. Fortunately, we

are able to recover all of these results by utilising the hypothesis testing framework. Detailed consideration of the

error in normal approximation also has implications for $\\chi^2$ and the log-likelihood ratio (LLR) based test statistics.

The normal approximation of the $\\chi^2$ test statistics has some serious and counter-intuitive restrictions. One such

restriction is that for multiple linear cryptanalysis as the number of linear approximations grows so does the requirement

on the number of plaintext-ciphertext pairs for the approximation to be proper. The issue of satisfactorily addressing the

problems with the application of the $\\chi^2$ test statistics remains open. For the LLR test statistics, previous work

used a normal approximation followed by another approximation to simplify the parameters of the normal approximation. We

derive the error bound for the normal approximation which turns out to be difficult to interpret. We show that the approximation

required for simplifying the parameters restricts the applicability of the result. Further, we argue that this approximation

is actually not required. More generally, the message of our work is that all cryptanalytic attacks should properly derive and

interpret the error bounds for any normal approximation that is made.

18:11 [Pub][ePrint]

We show the first positive results for the indifferentiability security of the confusion-diffusion networks (which are extensively used in the design of block ciphers and hash functions). In particular, our result shows that a constant number of confusion-diffusion rounds is sufficient to extend the domain of a public random permutation.

18:11 [Pub][ePrint]

A secure ad-hoc survey scheme enables a survey authority to independently (without any interaction) select an ad-hoc group of registered users based only on their identities (e.g., their email addresses), and create a survey where only selected users can anonymously submit exactly one response.

We present a formalization of secure ad-hoc surveys and present:

* an abstract provably-secure implementation based on standard cryptographic building blocks (which in particular are implied by the existence of enhanced trapdoor permutations in the CRS model);

* a practical instantiation of our abstract protocol, called ANONIZE, which is provably-secure in the random oracle model based on cryptographic assumptions on groups with bilinear maps.

As far as we know, ANONIZE constitutes the first implementation of a large-scale secure computation protocol (of non-trivial functionalities) that can scale to millions of users.