International Association for Cryptologic Research

# IACR News Central

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2015-06-30
21:17 [Pub][ePrint]

An important attack on multi-power RSA ($N=p^rq$) was introduced by Sarkar in 2014, by extending the small private exponent attack of Boneh and Durfee on classical RSA. In particular, he showed that $N$ can be factored efficiently for $r=2$ with private exponent $d$ satisfying $d 21:17 [Pub][ePrint] Ring signatures and group signatures are prominent cryptographic primitives offering a combination of privacy and authentication. They enable individual users to anonymously sign messages on behalf of a group of users. In ring signatures, the group, i.e.\\ the ring, is chosen in an ad hoc manner by the signer. In group signatures, group membership is controlled by a group manager. Group signatures additionally enforce accountability by providing the group manager with a secret tracing key that can be used to identify the otherwise anonymous signer when needed. Accountable ring signatures, introduced by Xu and Yung (CARDIS 2004), bridge the gap between the two notions. They provide maximal flexibility in choosing the ring, and at the same time maintain accountability by supporting a designated opener that can identify signers when needed. We revisit accountable ring signatures and offer a formal security model for the primitive. Our model offers strong security definitions incorporating protection against maliciously chosen keys and at the same time flexibility both in the choice of the ring and the opener. We give a generic construction using standard tools. We give a highly efficient instantiation of our generic construction in the random oracle model by meticulously combining Camenisch\'s group signature scheme (CRYPTO 1997) with a generalization of the one-out-of-many proofs of knowledge by Groth and Kohlweiss (EUROCRYPT 2015). Our instantiation yields signatures of logarithmic size (in the size of the ring) while relying solely on the well-studied decisional Diffie-Hellman assumption. In the process, we offer a number of optimizations for the recent Groth and Kohlweiss one-out-of-many proofs, which may be useful for other applications. Accountable ring signatures imply traditional ring and group signatures. We therefore also obtain highly efficient instantiations of those primitives with signatures shorter than all existing ring signatures as well as existing group signatures relying on standard assumptions. 20:15 [Job][New] Malicious cryptography is about using cryptography for cyber attacks. We have already seen applications of malicious cryptography in so-called ransomware. Sophisticated attackers may want to use cryptography to hide an attack, the target of the attack, the source of the attack or to protect attack infrastructure (botnets). The project goal is not to design sophisticated malware, but to understand the possible threats that we need to defend against. 18:17 [Pub][ePrint] Two lightweight block cipher families, SIMON and SPECK, have been proposed by researchers from the NSA recently. In this paper, we introduce Simeck, a new family of lightweight block ciphers that combines the good design components from both SIMON and SPECK, in order to devise even more compact and efficient block ciphers. For Simeck32/64, we can achieve 505 GEs (before the Place and Route phase) and 549 GEs (after the Place and Route phase), with the power consumption of 0.417$\\mu W$in CMOS 130nm ASIC, and 454 GEs (before the Place and Route phase) and 488 GEs (after the Place and Route phase), with the power consumption of 1.292$\\mu W$in CMOS 65nm ASIC. Furthermore, all of the instances of Simeck are smaller than the ones of hardware-optimized cipher SIMON in terms of area and power consumption in both CMOS 130nm and CMOS 65nm techniques. In addition, we also give the security evaluation of Simeck with respect to many traditional cryptanalysis methods, including differential attacks, linear attacks, impossible differential attacks, meet-in-the-middle attacks, and slide attacks. Overall, all of the instances of Simeck can satisfy the area, power, and throughput requirements in passive RFID tags. 18:17 [Pub][ePrint] As a sophisticated mechanism for secure fine-grained access control, ciphertext-policy attribute-based encryption (CP-ABE) is a highly promising solution for commercial applications such as cloud computing. However, there still exists one major issue awaiting to be solved, that is, the prevention of key abuse. Most of the existing CP-ABE systems missed this critical functionality, hindering the wide utilization and commercial application of CP-ABE systems to date. In this paper, we address two practical problems about the key abuse of CP-ABE: (1) The key escrow problem of the semi-trusted authority; and, (2) The malicious key delegation problem of the users. For the semi-trusted authority, its misbehavior (i.e., illegal key (re-)distribution) should be caught and prosecuted. And a user, his/her malicious behavior (i.e., illegal key sharing) need be traced. We affirmatively solve these two key abuse problems by proposing the first accountable authority CP-ABE with white-box traceability that supports policies expressed in any monotone access structures. Moreover, we provide an auditor to judge publicly whether a suspected user is guilty or is framed by the authority. 18:17 [Pub][ePrint] The Diffie-Hellman problem as a cryptographic primitive plays an important role in modern cryptology. The Bit Security or Hard-Core Bits of Diffie-Hellman problem in arbitrary finite cyclic group is a long-standing open problem in cryptography. Until now, only few groups have been studied. Hyperelliptic curve cryptography is an alternative to elliptic curve cryptography. Due to the recent cryptanalytic results that the best known algorithms to attack hyperelliptic curve cryptosystems of genus$g

16:29 [Job][New]

We offer two, 3-year Ph.D. scholarships in area of design and cryptanalysis of authenticated encryption schemes.

Working place: Kielce, POLAND

In the second part of the scholarship timeline, it may be possible to continue research in Australia, under supervision of Josef Pieprzyk, QUT, Brisbane.

2015-06-29
21:24 [Event][New]

Submission: 2 October 2015
From February 22 to February 26

2015-06-28
21:17 [Pub][ePrint]

We proposed a new secure oblivious transfer protocol from indistinguishability obfuscation in this paper. Our main technical tool

is the candidate indistinguishability obfuscation introduced in [1] and

a dual-mode cryptosystem proposed in [2]. Following their steps, we

presents a new k-out-of-l oblivious transfer protocol, its realization from

DDH is described in this paper, in which we combined indistinguishability obfuscation with the dual-mode cryptosystem. The security of our

scheme mainly relies on the indistinguishability of the obf-branches ( corresponding to the two modes in dual-mode model). Our paper explores

a new way for the application of indistinguishability obfuscation.

21:17 [Pub][ePrint]

In this paper, we first demonstrate a new Differential Power Analysis (DPA) attack technique against the Grain family of stream ciphers (Grain v1 and Grain-128) by resynchronizing the cipher multiple times with the same value of the secret \\emph{key} and randomly generated different initialization vectors (IVs). Subsequently, we develop a combined side channel and fault analysis attack strategy targeting various fault attack countermeasures for the Grain cipher family.

We considered clock glitch induced faults occurring in practice for a hardware implementation of the cipher to devise our novel attack technique. Our proposed combined attack strategy works well even if the \\emph{useful} ciphertexts are not available to the adversary.

Further, the power trace classifications of a Grain cipher implementation on SASEBO G-II standard side channel evaluation board is shown in order to validate our proposed attack against the cipher.

The captured power traces were analyzed using Least Squares Support Vector Machine (LS-SVM) learning algorithm based multiclass classifiers to classify the power traces into the respective

Hamming distance (HD) classes. To extract power samples with high information about HD classes, Signal-to-noise ratio (SNR) metric

was chosen for feature selection. The experimental results of power trace classifications of test set showed a high success rate of $98\\%$ when the five largest SNR sample instants over a clock cycle were chosen as features. Our proposed attack strategy can also be extended to other stream cipher designs based on Fibonacci

configured shift registers.

21:17 [Pub][ePrint]

We recall why linear codes with complementary duals (LCD codes) play a role in counter-measures to passive and active side-channel analyses on embedded cryptosystems. The rate and the minimum distance of such LCD codes must be as large as possible. We investigate primary constructions of such codes, in particular with cyclic codes, specifically with generalized residue codes, and we study their idempotents. We study those secondary constructions which preserve the LCD property, and we characterize conditions under which codes obtained by puncturing, shortening or extending codes, or obtained by the Plotkin sum, can be LCD.