International Association for Cryptologic Research

# IACR News Central

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2014-07-29
03:52 [Event][New]

Submission: 17 October 2014
From November 17 to November 19
Location: Kuala Lumpur, Malaysia

03:52 [Event][New]

Submission: 17 October 2014
From November 17 to November 19
Location: Kuala Lumpur, Malaysia

2014-07-27
09:57 [Job][New]

The High Assurance Software Laboratory (HASLab) at INESC TEC has an opening for a 2 year Post-Doc position.

The position is within the cryptography and information security group in the HASLab.

The group is actively working on: provable security, domain-specific languages and software development tools for cryptography, efficient implementation of cryptographic software, and formal verification of cryptographic proofs and implementations.

We are looking for a highly motivated researcher with a recent Ph.D. and background in at least one of the following fields:

provable security,

efficient implementation of cryptography,

programming languages and verification,

and an interest in carrying out research at their intersection.

The position starts from November 2014. The salary is around 18K euros per year after tax. The working language is English.

Applications should arrive no later than September 19, 2014 and should include a CV, a cover letter, and the names and contact details for two references.

2014-07-25
15:17 [Pub][ePrint]

In this paper we study a scan based side channel attack

against the Grain family of stream ciphers. The attack works

because scan chain test of circuits can be transformed into a

powerful cryptographic attack due to the properties of scan

based technique. So as a result the attack targets the test

circuitry. We show how the attacker gains the knowledge about

the locations of internal state bits of the NFSR and the LFSR and

how he finds the secret key.

15:17 [Pub][ePrint]

The existence of succinct non-interactive arguments for NP (i.e.,

non-interactive computationally-sound proofs where the verifier\'s

work is essentially independent of the complexity of the NP

nondeterministic verifier) has been an intriguing question for the

past two decades. Other than CS proofs in the random oracle model

[Micali, FOCS \'94], the only existing candidate construction is

based on an elaborate assumption that is tailored to a specific

protocol [Di Crescenzo and Lipmaa, CiE \'08].

We formulate a general and relatively natural notion of an

\\emph{extractable collision-resistant hash function (ECRH)} and show

that, if ECRHs exist, then a modified version of Di Crescenzo and

Lipmaa\'s protocol is a succinct non-interactive argument for

NP. Furthermore, the modified protocol is actually a succinct

non-interactive \\emph{adaptive argument of knowledge (SNARK).} We

then propose several candidate constructions for ECRHs and

relaxations thereof.

We demonstrate the applicability of SNARKs to various forms of delegation of computation, to succinct non-interactive zero knowledge arguments, and to succinct two-party secure computation. Finally, we show that SNARKs essentially imply the existence of ECRHs, thus demonstrating the necessity of the assumption.

Going beyond $\\ECRH$s, we formulate the notion of {\\em extractable

one-way functions ($\\EOWF$s)}. Assuming the existence of a natural

variant of $\\EOWF$s, we construct a $2$-message

selective-opening-attack secure commitment scheme and a 3-round

zero-knowledge argument of knowledge. Furthermore, if the $\\EOWF$s are

concurrently extractable, the 3-round zero-knowledge protocol is also

concurrent zero-knowledge.

Our constructions circumvent previous black-box impossibility

results regarding these protocols by relying on $\\EOWF$s as the non-black-box component in the security reductions.

13:35 [Event][New]

From October 13 to October 16
Location: Porto, Portugal

2014-07-24
15:17 [Pub][ePrint]

After more than a decade of usage, bilinear groups have established their place in the cryptographic canon by enabling the construction of many advanced cryptographic primitives. Unfortunately, this explosion in functionality has been accompanied by an analogous growth in the complexity of the assumptions used to prove security. Many of these assumptions have been gathered under the umbrella of the \"uber-assumption,\" yet certain classes of these assumptions -- namely, q-type assumptions -- are stronger and require larger parameter sizes than their static counterparts.

In this paper, we show that in certain groups, many classes of q-type assumptions are in fact implied by subgroup hiding (a well-established, static assumption). Our main tool in this endeavor is the dual-system technique, as introduced by Waters in 2009. As a case study, we first show that in composite-order groups, we can prove the security of the Dodis-Yampolskiy PRF based solely on subgroup hiding and allow for a domain of arbitrary size (the original proof only allowed a polynomially-sized domain). We then turn our attention to classes of q-type assumptions and show that they are implied -- when instantiated in appropriate groups -- solely by subgroup hiding. These classes are quite general and include assumptions such as q-SDH. Concretely, our result implies that every construction relying on such assumptions for security (e.g., Boneh-Boyen signatures) can, when instantiated in appropriate composite-order bilinear groups, be proved secure under subgroup hiding instead.

15:17 [Pub][ePrint]

This paper analyzes the cost of breaking ECC under the following assumptions: (1) ECC is using a standardized elliptic curve that was actually chosen by an attacker; (2) the attacker is aware of a vulnerability in some curves that are not publicly known to be vulnerable.

This cost includes the cost of exploiting the vulnerability, but also the initial cost of computing a curve suitable for sabotaging the standard. This initial cost depends upon the acceptability criteria used by the public to decide whether to allow a curve as a standard, and (in most cases) also upon the chance of a curve being vulnerable.

This paper shows the importance of accurately modeling the actual acceptability criteria: i.e., figuring out what the public can be fooled into accepting. For example, this paper shows that plausible models of the \"Brainpool acceptability criteria\" allow the attacker to target a one-in-a-million vulnerability.

15:17 [Pub][ePrint]

Differential Fault Analysis is a powerful cryptanalytic tool to reveal secret

keys of cryptographic algorithms.

By corrupting the computation of an algorithm, an attacker gets

In 2012, several Differential Fault Analyses on the AES cipher were

analyzed

from an information-theoretic perspective.

This analysis exposed whether or not the leaked information was fully exploited.

It revealed if an analysis was already optimal or if it could still be improved.

We applied the same approach to all existing Differential Fault Analyses

on the CLEFIA cipher.

We show that only some of these attacks are already optimal.

We improve those analyses which did not exploit all information.

With one exception, all attacks against CLEFIA-128 reach the theoretical limit

after our improvement.

Our improvement of an attack against CLEFIA-192 and CLEFIA-256 reduces the

number of fault injections to the lowest possible number reached to date.

15:17 [Pub][ePrint]

In this paper a new public key system based on polynomials over finite fields GF(2) is developed.The security of the system is based on the difficulty of solving discrete logarithms over GF(2^k)

with sufficiently large k. The presented system has all features of ordinary public key schemes such as public key encryption and digital signatures. The security and implementation aspects of the presented system are also introduced along with comparison with other well known public- key systems.

15:17 [Pub][ePrint]

At Crypto 2013, Coron, Lepoint, and Tibouchi~(CLT) proposed a practical Graded Encoding Scheme (GES) over the integers, which has very similar cryptographic features to ideal multilinear maps. In fact, the scheme of Coron~{\\em et al.} is the second proposal of a secure GES, and has advantages over the first scheme of Garg, Gentry, and Halevi~(GGH). For example, unlike the GGH construction, the subgroup decision assumption holds in the CLT construction. Immediately following the elegant innovations of the GES, numerous GES-based cryptographic applications were proposed. Although these applications rely on the security of the underlying GES, the security of the GES has not been analyzed in detail, aside from the original papers produced by Garg~{\\em et~al.} and Coron~{\\em et~al.}

We present an attack algorithm against the system parameters of the CLT GES. The proposed algorithm\'s complexity $\\tilde\\bO(2^{\\rho/2})$ is exponentially smaller than $\\tilde\\bO(2^{\\rho})$ of the previous best attack of Coron~{\\em et al.}, where $\\rho$ is a function of the security parameter. Furthermore, we identify a flaw in the generation of the zero-testing parameter of the CLT GES, which drastically reduces the running time of the proposed algorithm. The experimental results demonstrate the practicality of our attack.