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06:17 [Pub][ePrint] Non-malleability under Selective Opening Attacks: Implication and Separation, by Zhengan Huang and Shengli Liu and Xianping Mao and Kefei Chen

  We formalize the security notions of non-malleability under selective opening attacks (NM-SO security) in two approaches: the indistinguishability-based approach and the simulationbased approach. We explore the relations between NM-SO security notions and the known selective

opening security notions, and the relations between NM-SO security notions and the standard non-malleability notions.

06:17 [Pub][ePrint] Leakage-Resilient Cryptography over Large Finite Fields: Theory and Practice, by Marcin Andrychowicz and Daniel Masny and Edoardo Persichetti

  Information leakage is a major concern in modern day IT-security. In fact, a malicious user is often able to extract

information about private values from the computation performed on the

devices. In specific settings, such as RFID, where a low computational complexity is required, it is hard to apply standard techniques to achieve resilience against this kind of attacks.

In this paper, we present a framework to make cryptographic

primitives based on large finite fields robust against information leakage

with a bounded computational cost.

The approach makes use

of the inner product extractor and guarantees security in the presence of

leakage in a widely accepted model. Furthermore, we show how to apply the proposed

techniques to the authentication protocol Lapin, and we compare it to existing


06:17 [Pub][ePrint] Practical Divisible E-Cash, by Patrick Märtens

  Divisible e-cash systems allow a user to withdraw a wallet containing K coins and to spend k < K + 1 coins in a single operation, respectively. Independent of the new work of Canard, Pointcheval, Sanders and Traoré (Proceedings of PKC \'15) we present a practical and secure divisible e-cash system in which the bandwidth of each protocol is constant while the system fulfills the standard security

requirements (especially which is unforgeable and truly anonymous) in the random oracle model. In other existing divisible e-cash systems that are truly anonymous, either the bandwidth of withdrawing

depends on K or the bandwidth of spending depends on k. Moreover, using some techniques of the work of Canard, Pointcheval, Sanders and Traoré we are also able to prove the security in the standard model.

Furthermore, we show an efficient attack against the unforgeability of Canard and Gouget\'s divisible e-cash scheme (FC \'10).

Finally, we extend our scheme to a divisible e-cash system that provides withdrawing and spending of an arbitrary value of coins (not necessarily a power of two) and give an extension to a fair e-cash


06:17 [Pub][ePrint] Point Decomposition Problem in Binary Elliptic Curves, by Koray Karabina

  We analyze the point decomposition problem (PDP) in binary elliptic curves. It is known that PDP in an elliptic curve group can be reduced to solving a particular system of multivariate non-linear system of equations derived from the so called Semaev summation polynomials.

We modify the underlying system of equations by introducing some auxiliary variables. We argue that the trade-off between lowering the degree of Semaev polynomials and increasing the number of variables is worth.

06:17 [Pub][ePrint] Hybrid Publicly Verifiable Computation, by James Alderman and Christian Janson and Carlos Cid and Jason Crampton

  Publicly Verifiable Outsourced Computation (PVC) allows weak devices to delegate computations to more powerful servers, and to verify the correctness of results.

Delegation and verification rely only on public parameters, and thus PVC lends itself to large multi-user systems where entities need not be registered, yet in such settings the individual user requirements may be diverse.

In this paper, we introduce Hybrid PVC (HPVC) which, with a single setup stage, provides a flexible solution to outsourced computation supporting standard PVC, the enforcement of access control policies restricting the servers that may evaluate a given computation, and a reversed model of PVC which we call Verifiable Delegable Computation (VDC) where data is held remotely by servers. We provide formal frameworks and constructions for such systems.

06:17 [Pub][ePrint] Size-Hiding in Private Set Intersection: what can be done and how to do it without random oracles, by Paolo D\'Arco and Maria Isabel Gonzalez Vasco and Angel L. Perez del Pozo and Clauido Soriente

  In this paper we focus our attention on private set intersection protocols, through which two parties, each holding a set of inputs drawn from a ground set, jointly compute the intersection of their sets. Ideally, no further information than which elements are actually shared is compromised to the other party, yet the input set sizes are often considered as admissible leakage. Considering the (more restricted) size-hiding scenario, we are able to:

- prove that it is impossible to realize an unconditionally secure set intersection protocol (size-hiding or not);

- prove that unconditionally secure size-hiding set intersection is possible in a model where a set up authority provides certain information to the two parties and disappears;

- provide several new computationally secure size-hiding set intersection protocols.

Regarding the latter, in particular we provide a new generic construction without random oracles for the unbalanced setting,

where only the client gets the intersection and hides the size of its set of secrets. The main tool behind this design are smooth projective hash functions for languages derived from perfectly-binding commitments. We stand on the seminal ideas of Cramer-Shoup and Gennaro-Lindell, which have already found applications in several other contexts, such as password-based authenticated key exchange and oblivious transfer.

06:17 [Pub][ePrint] Transformation-Based Outsourcing of Linear Equation Systems over Real Numbers, by Peeter Laud and Alisa Pankova

  This paper studies the possibility of achieving indistinguishability-based security in privately outsourcing linear equation systems over real numbers. The particular task is to solve a full-rank (n x n) system Ax = b. Since the most complex part of this task is inverting A, the problem can be reduced to outsourcing of a square matrix inverse computation. Although outsourcing matrix inverse is trivial for matrices over finite fields, it is not so easy for matrices over real numbers. We study the class of affine transformations for matrices over real numbers, find out which forms are possible at all, and state some properties that the transformation and the initial matrices must satisfy in order to make the initial matrices perfectly (or statistically) indistinguishable after applying the transformation. This paper provides both possibility and impossibility results.

06:17 [Pub][ePrint] Efficient, Pairing-Free, One Round Attribute-Based Authenticated Key Exchange, by Suvradip Chakraborty and Srinivasan Raghuraman and Pandu Rangan C

  In this paper, we present a single round two-party attribute-based authenticated key exchange protocol. Since pairing is a costly operation and the composite order groups must be very large to ensure security, we focus on pairing free protocols in prime order groups. We propose a new protocol that is pairing free, working in prime order group and having tight reduction to Strong Diffie Hellman (SDH) problem under the Attribute-based CK model which is a natural extension of the CK model for the public key setting. Thus, the first major advantage is that smaller key sizes are sufficient to achieve

comparable security. Our scheme has several other advantages. The major one being the capability to handle active adversaries. All the previous Attribute-Based authenticated key exchange protocols can offer security only under passive adversaries. Our protocol recognizes the corruption by an active adversary and aborts the process. Ours is the first scheme achieving this property. We also show how to modify our construction to achieve anonymity of access structure of users. Our attribute-based authenticated key exchange is also the first that enjoys this property. In addition to this property, our scheme satisfies other security properties that are not covered by CK model such as forward secrecy, key compromise impersonation attacks and ephemeral key compromise impersonation attacks.

06:17 [Pub][ePrint] A Note on Lower Bounds for Non-interactive Message Authentication Using Weak Keys, by Divesh Aggarwal and Alexander Golovnev

  In this note, we prove lower bounds on the amount of entropy of random sources necessary for secure message authentication. We consider the problem of non-interactive c-time message authentication using a weak secret key having min-entropy k. We show that existing constructions using (c+1)-wise independent hash functions are optimal.

This result resolves one of the main questions left open by the work of Dodis and Spencer [DS02] who considered this problem for one-time message authentication of one-bit messages.

03:17 [Pub][ePrint] Certificate-Based Encryption Resilient to Key Leakage, by Qihong Yu and Jiguo Li and Yichen Zhang and Wei Wu and Xinyi Huang and Yang Xiang

  Certificate-based encryption (CBE) is an important class of public key encryption but the existing schemes are secure only under the premise that the decryption key (or private key) and master private key are absolutely secret. In fact, a lot of side channel attacks and cold boot attacks can leak secret information of a cryptographic system. In this case, the security of the cryptographic system is destroyed, so a new model called leakage-resilient (LR) cryptography is introduced to solve this problem. While some traditional public key encryption and identity-based encryption with resilient-leakage schemes have been constructed, as far as we know, there is no leakage-resilient scheme in certificate-based cryptosystems. This paper puts forward the first certificate-based encryption scheme which can resist not only the decryption key leakage but also the master secret key leakage. Based on composite order bilinear group assumption, the security of the scheme is proved by using dual system encryption. The relative leakage rate of key is close to 1/3.

03:17 [Pub][ePrint] Query-Complexity Amplification for Random Oracles, by Grégory Demay and Peter Gaži and Ueli Maurer and Björn Tackmann

  Increasing the computational complexity of evaluating a hash

function, both for the honest users as well as for an

adversary, is a useful technique employed for example in

password-based cryptographic schemes to impede brute-force

attacks, and also in so-called proofs of work (used in

protocols like Bitcoin) to show that a certain amount of

computation was performed by a legitimate user. A natural

approach to adjust the complexity of a hash function is to

iterate it $c$~times, for some parameter

$c$, in the hope that any query to the scheme

requires $c$ evaluations of the underlying

hash function. However, results by Dodis et al. (Crypto

2012) imply that plain iteration falls short of achieving

this goal, and designing schemes which provably have such a

desirable property remained an open problem.

This paper formalizes explicitly what it means for a given

scheme to amplify the query complexity of a hash function.

In the random oracle model, the goal of a secure

query-complexity amplifier (QCA) scheme is captured as

transforming, in the sense of indifferentiability, a random

oracle allowing $R$ queries (for the adversary)

into one provably allowing only $r < R$

queries. Turned around, this means that making

$r$ queries to the scheme requires at least

$R$ queries to the actual random oracle. Second,

a new scheme, called collision-free iteration, is proposed and

proven to achieve $c$-fold QCA for both the

honest parties and the adversary, for any fixed