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10:17 [Pub][ePrint] Cryptanalysis of FIDES, by Itai Dinur and Jérémy Jean

  FIDES is a lightweight authenticated cipher, presented at CHES 2013.

The cipher has two version, providing either 80-bit or 96-bit

security. In this paper, we describe internal state-recovery attacks

on both versions of FIDES, and show that once we recover the internal

state, we can use it to immediately forge any message. Our attacks are

based on a guess-and-determine algorithm, exploiting the slow

diffusion of the internal linear transformation of FIDES. Our most

basic attacks have time complexities of 2^{75} and 2^{90} for FIDES-80

and FIDES-96, respectively, use a very small amount of memory, and

their most distinctive feature is their very low data complexity: the

attacks require at most 24 bytes of an arbitrary plaintext and its

corresponding ciphertext, in order to break the cipher with

probability 1. In addition to the basic attacks, we describe optimized

attacks which exploit additional data in order to reduce the time

complexities to 2^{73} and 2^{88} for FIDES-80 and FIDES-96,


01:17 [Pub][ePrint] Computing Discrete Logarithms in F_{3^{6*137}} using Magma , by Gora Adj and Alfred Menezes and Thomaz Oliveira and Francisco Rodríguez-Henríquez

  We show that a Magma implementation of Joux\'s new L[1/4] algorithm

can be used to compute discrete logarithms in the 1303-bit finite field

F_{3^{6*137}} with very modest computational resources.

Our implementation illustrates the effectiveness of Joux\'s algorithm

for computing discrete logarithms in small-characteristic finite

fields which are not Kummer or twisted-Kummer extensions.

22:17 [Pub][ePrint] Masking and Leakage-Resilient Primitives: One, the Other(s) or Both?, by Sonia Belaïd, and Vincent Grosso and François-Xavier Standaert

  Securing cryptographic implementations against side-channel attacks is one of the most important challenges in modern cryptography. Many countermeasures have been introduced for this purpose, and analyzed in specialized security models. Formal solutions have also been proposed to extend the guarantees of provable security to physically observable devices. Masking and leakage-resilient cryptography are probably the most investigated and best understood representatives of these two approaches. Unfortunately, claims whether one, the other or their combination provides better security at lower cost remained vague so far. In this paper, we provide the first comprehensive treatment of this important problem. For this purpose, we analyze whether cryptographic implementations can be security-bounded, in the sense that the time complexity of the best side-channel attack is lower-bounded, independent of the number of measurements performed. Doing so, we first put forward a significant difference between stateful primitives such as leakage-resilient PRGs (that easily ensure bounded security), and stateless ones such as leakage-resilient PRFs (that hardly do). We then show that in practice, leakage-resilience alone provides the best security vs. performance tradeoff when bounded security is achievable, while masking alone is the solution of choice otherwise. That is, we highlight that~one (x)or the other approach should be privileged, which contradicts the usual intuition that physical security is best obtained by combining countermeasures.

Besides, our experimental results underline that despite defined in exactly the same way, the bounded leakage requirement in leakage-resilient PRGs and PRFs imply significantly different challenges for hardware designers. Namely, such a bounded leakage is much harder to guarantee for stateless primitives (like PRFs) than for statefull ones (like PRGs). As a result, constructions of leakage-resilient PRGs and PRFs proven under the same bounded leakage assumption, and instantiated with the same AES implementation, may lead to different practical security levels.

22:17 [Pub][ePrint] The Fourier Entropy-Influence conjecture holds for a log-density 1 class of cryptographic Boolean functions, by Sugata Gangopadhyay and Pantelimon Stanica

  We consider the Fourier Entropy-Influence (FEI) conjecture in the context of cryptographic Boolean functions. We show that the FEI conjecture is true for the functions satisfying the strict avalanche criterion, which forms a subset of asymptotic log--density~$1$ in the set of all Boolean functions. Further, we prove that the FEI conjecture is satisfied for plateaued Boolean functions, monomial algebraic normal form (with the best involved constant), direct sums, as well as concatenations of Boolean functions. As a simple consequence of these general results we find that each affine equivalence class of quadratic Boolean functions contains at least one function satisfying the FEI conjecture. Further, we propose some ``leveled\'\' FEI conjectures.

22:17 [Pub][ePrint] Security Enhanced Anonymous Multi-Server Authenticated Key Agreement Scheme using Smart Card and Biometrics, by Younsung Choi

  Chuang and Chen propose an anonymous multi server authenticated key agreement scheme based on trust computing using smart card, password, and biometrics. Chuang and Chen say that this scheme not only supports multi-server but also achieves security requirements. but this scheme is vulnerable to masquerade attack, smart card attack, DoS attack and insufficient for perfect forward secrecy. To solve problems, this paper proposes security enhanced anonymous multi server authenticated key agreement scheme using smart card and biometrics.

22:17 [Pub][ePrint] Low Probability Differentials and the Cryptanalysis of Full-Round CLEFIA-128, by Sareh Emami and San Ling and Ivica Nikolic and Josef Pieprzyk and Huaxiong Wang

  So far, low probability differentials for the key schedule of block ciphers have been used as a straightforward proof of security against related-key differential attacks. To achieve the resistance, it is believed that for cipher with $k$-bit key it suffices the upper bound on the probability to be $2^{-k}$. Surprisingly, we show that this reasonable assumption is incorrect, and the probability should be (much) lower than $2^{-k}$. Our counter example is a related-key differential analysis of the block cipher CLEFIA-128. We show that although the key schedule of CLEFIA-128 prevents differentials with a probability higher than $2^{-128}$, the linear part of the key schedule that produces the round keys, and the Feistel structure of the cipher, allow to exploit particularly chosen differentials with a probability as low as $2^{-128}$. CLEFIA-128 has $2^{14}$ such differentials, which translate to $2^{14}$ pairs of weak keys. The probability of each differential is too low for attacks, but the weak keys have a special structure which allows with a divide-and-conquer approach to gain advantage of $2^7$ over generic attacks. We exploit the advantage and give a membership test for the weak-key class,

provide analysis in the hashing mode, and show the importance for the secret-key mode. The proposed analysis has been tested with computer experiments on small-scale variants of CLEFIA-128.

Our results do not threaten the practical use of CLEFIA.

14:59 [PhD][New] Constantin Catalin Dragan: Security of CRT-based Secret Sharing Schemes

  Name: Constantin Catalin Dragan
Topic: Security of CRT-based Secret Sharing Schemes
Category: (no category)


The Chinese Remainder Theorem (CRT) is a very useful tool in many areas of theoretical and practical cryptography. One of these areas is the theory of threshold secret sharing schemes. A (t+1,n)-threshold secret sharing scheme is a method of partitioning a secret among n users by providing each user with a share of the secret such that any t+1 users can uniquely reconstruct the secret by pulling together their shares. Several threshold schemes based on CRT are known. These schemes use sequences of pairwise co-prime positive integers with special properties. The shares are obtained by dividing the secret or a secret-dependent quantity by the numbers in the sequence and collecting the remainders. The secret can be reconstructed by some sufficient number of shares by using CRT. It is well-known that the CRT-based threshold secret sharing schemes are not perfect (and, therefore, not ideal) but some of them are asymptotically perfect and asymptotically ideal and perfect zero-knowledge if sequences of consecutive primes are used for defining them.


\r\nIn this thesis we introduce (k-)compact sequences of co-primes and their applications to the security of CRT-based threshold secret sharing schemes is thorough investigated. Compact sequences of co-primes may be significantly denser than sequences of consecutive primes of the same length, and their use in the construction of CRT-based threshold secret sharing schemes may lead to better security properties. Concerning the asymptotic idealness property for CRT-based threshold schemes, we have shown there exists a necessary and sufficient condition for the Goldreich-Ron-Sudan (GRS) scheme and Asmuth-Bloom scheme if and only if (1-)compact sequences of co-primes are used. Moreover, the GRS and Asmuth-Bloom schemes based on k-compact sequences of co-primes are asymptotically perfect and perfect zero-knowledge. The Mignotte scheme is far from being asymptotically perfect [...]

14:59 [PhD][New] Ferucio Laurentiu Tiplea

  Name: Ferucio Laurentiu Tiplea

14:58 [PhD][New] Ruxandra F. Olimid: Secret Sharing-based Group Key Establishment

  Name: Ruxandra F. Olimid
Topic: Secret Sharing-based Group Key Establishment
Category: (no category)

Description: Group applications permit multiple users to share resources or perform collaborative tasks while providing differentiate rights or responsibilities within the group. Examples include text communication, audio, video or web conferences, data sharing or collaborative computing.\r\n\r\n
\r\nSecurity represents an important aspect for group applications. It is a challenging task to deal with, especially when the group size is large and the members are spread across different (location or networks) areas, with diverse protection mechanisms. In order to obtain the main cryptographic properties as confidentiality, authenticity and integrity it is usually required that the group members previously share a common secret group key. This is achieved as theoutput of a group key establishment protocol.\r\n\r\n
\r\nThe thesis restricts to group key establishment protocols based on secret sharing, a primitive that divides a secret into multiple shares such that only authorized subset of shares allow reconstruction. Although secret sharing brings several advantages when it is used as a building block of group key establishment protocols, two important shortcomings currently exist: (1) several insecure proposals were published in the last years and (2) very few constructions rely on a security proof. We address both this issues in the present work.\r\n\r\n
\r\nThe first part of the dissertation focuses on the underlying secret sharing schemes. We review a non-classical approach of secret sharing, de ne a new visual secret sharing scheme and analyze the possibility of malicious manufacturing of the sharing device. The second part of the thesis concentrates on group key establishment constructions that use secret sharing. We introduce a multitude of attacks against recent protocols and therefore highlight the necessity of security proofs. We review the properties that impose a sufficient level of security and briefly analyze the formal models of security. Finally, we introduc[...]

14:58 [PhD][New] Adrian Atanasiu

  Name: Adrian Atanasiu

13:26 [Job][New] Postdoctoral and Internship Positions, MICROSOFT RESEARCH, Redmond, Washington USA

  Microsoft Research invites applications from graduate students and recent Ph.D.s for Postdoctoral and Internship positions in the Microsoft Research Cryptography Group. Number Theory candidates should have interest/experience in one or more of the following areas: algorithmic/arithmetic/algebraic number theory, elliptic and hyperelliptic curve cryptography, pairing-based cryptosystems, lattice-based cryptography. Cryptography candidates should have research interests in at least one of the following: protocols, security models, cryptanalysis, hash functions, applied or theoretical cryptography.

Post-docs and interns will be in residence at Microsoft Research Redmond, the main campus of Microsoft\\\'s basic research division with over four hundred researchers in dozens of areas of computer science research. Researchers benefit from close proximity to Microsoft product units, collaborative relations and joint seminars with University of Washington, and an active research environment. For more information about MSR Redmond and the Cryptography group see: and

The post-doctoral positions offer a competitive salary, benefits, and a relocation allowance. The term is for two years; the start date is July 1, 2014. Post-docs will report to Dr. Kristin Lauter, Research Manager for the MSR Crypto Group. Internships for graduate students will be for 10-12 weeks in Summer 2014, with flexible start date.