International Association for Cryptologic Research

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2015-03-23
13:01 [Event][New] School on Computer-aided Cryptography

  From June 1 to June 4
Location: College Park, USA
More Information: https://www.easycrypt.info/trac/wiki/SchoolUMD2015




2015-03-22
20:21 [Event][New] S3: SAC Summer School

  From August 10 to August 12
Location: Sackville, Canada
More Information: http://mta.ca/sac2015/s3.html


09:17 [Pub][ePrint] Lightweight MDS Involution Matrices, by Siang Meng Sim and Khoongming Khoo and Fr\\\'ed\\\'erique Oggier and Thomas Peyrin

  In this article, we provide new methods to look for lightweight MDS matrices, and in particular involutory ones. By proving many new properties and equivalence classes for various MDS matrices constructions such as circulant, Hadamard, Cauchy and Hadamard-Cauchy, we exhibit new search algorithms that greatly reduce the search space and make lightweight MDS matrices of rather high dimension possible to find. We also explain why the choice of the irreducible polynomial might have a significant impact on the lightweightness, and in contrary to the classical belief, we show that the Hamming weight has no direct impact. Even though we focused our studies on involutory MDS matrices, we also obtained results for non-involutory MDS matrices. Overall, using Hadamard or Hadamard-Cauchy constructions, we provide the (involutory or non-involutory) MDS matrices with the least possible XOR gates for the classical dimensions 4x4, 8x8, 16x16 and 32x32 in GF(2^4) and GF(2^8). Compared to the best known matrices, some of our new candidates save up to 50% on the amount of XOR gates required for an hardware implementation. Finally, our work indicates that involutory MDS matrices are really interesting building blocks for designers as they can be implemented with almost the same number of XOR gates as non-involutory MDS matrices, the latter being usually non-lightweight when the inverse matrix is required.



09:17 [Pub][ePrint] Exhausting Demirci-Selçuk Meet-in-the-Middle Attacks against Reduced-Round AES, by Patrick Derbez and Pierre-Alain Fouque

  In this paper, we revisit Demirci and Selçuk meet-in-the-middle attacks on AES. We find a way to automatically model SPN block cipher and meet-in-the-middle attacks that allows to perform exhaustive search of this kind of attacks. This search uses the tool developed by Bouillaguet, Derbez and Fouque at CRYPTO 2011 as a subroutine to solve specific systems. We also take into account ideas introduced by Dunkelman, Keller and Shamir at ASIACRYPT 2010 which can be seen as a new tradeoff of the classical time/memory tradeoff used by Demirci and Selçuk. As a result, we automatically recover all the recent improved attacks of Derbez, Fouque and Jean on AES and we show new improved attacks against 8-rounds of AES-192 and AES-256.



09:17 [Pub][ePrint] Computational Aspects of Correlation Power Analysis, by Paul Bottinelli and Joppe W. Bos

  Since the discovery of simple power attacks, the cryptographic research community has developed significantly more advanced attack methods. The idea behind most algorithms remains to perform a statistical analysis by correlating the power trace obtained when executing a cryptographic primitive to a key-dependent guess. With the advancements of cryptographic countermeasures, it is not uncommon that sophisticated (higher-order) power attacks require computation on many millions of power traces in order to find the desired correlation.

In this paper, we study the computational aspects of calculating the most widely used correlation coefficient: the Pearson product-moment correlation coefficient. We study various time-memory trade-off techniques which apply specifically to the cryptologic setting and present methods to extend already completed computations using incremental versions. Moreover, we show how this technique can be applied to second-order attacks, reducing the attack cost significantly when adding new traces to a dataset. We also present methods which allow one to split the potentially huge trace set into smaller, more manageable chunks in order to reduce the memory requirements. Our concurrent implementation of these techniques highlights the benefits of this approach as it allows efficient computations on power measurements consisting of hundreds of gigabytes on a single modern workstation.



09:17 [Pub][ePrint] Research Perspectives and Challenges for Bitcoin and Cryptocurrencies, by Joseph Bonneau, Andrew Miler, Jeremy Clark, Arvind Narayanan, Joshua A. Kroll, Edward W. Felten

  Bitcoin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch in 2009, Bitcoin grew to comprise billions of dollars of economic value, even while the body of published research and security analysis justifying the system\'s design was negligible. In the ensuing years, a growing literature has identified hidden-but-important properties of the system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. This interest has been complemented by a large and vibrant community of open-source developers who steward the system, while proposing and deploying numerous modifications and extensions.

We provide the first systematic exposition of the second generation of cryptocurrencies, including Bitcoin and the many alternatives that have been implemented as alternate protocols or ``altcoins.\'\' Drawing from a scattered body of knowledge, we put forward three key components of Bitcoin\'s design that can be decoupled, enabling a more insightful analysis of Bitcoin\'s properties and its proposed modifications and extensions. We contextualize the literature into five central properties capturing blockchain stability. We map the design space for numerous proposed modification, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We focus on anonymity issues in Bitcoin and provide an evaluation framework for analyzing a variety of proposals for enhancing unlinkability. Finally we provide new insights on a what we term disintermediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disintermediation strategies and provide a detailed comparative cost analysis.



09:17 [Pub][ePrint] A look at the PGP ecosystem through the key server data, by Hanno Böck

  PGP-based encryption systems use a network of key servers to share public keys. These key server operate on an add only basis, thus the data gives us access to PGP public keys from over 20 years of PGP usage. Analyzing this data allows searching for cryptographic weaknesses in large scale.

I created a parser script that puts the raw cryptographic data of the PGP keys into a database. Doing this allows large scale searches for well-known vulnerabilities. DSA signatures with a duplicate $k$ value due to bad random numbers allow the calculation of the private key. Similarly analyzing RSA keys for shared prime factors allows factoring the modulus and thus also regenerating the private key.

A small number of breakable keys due to these weaknesses were found.



09:17 [Pub][ePrint] Eclipse Attacks on Bitcoin\'s Peer-to-Peer Network, by Ethan Heilman. Alison Kendler, Aviv Zohar, Sharon Goldberg

  We present eclipse attacks on bitcoin\'s peer-to-peer network. Our attack allows an adversary controlling a sufficient number of IP addresses to monopolize all connections to and from a victim bitcoin node. The attacker can then exploit the victim for attacks on bitcoin\'s mining and consensus system, including N-confirmation double spending, selfish mining, and adversarial forks in the blockchain. We take a detailed look at bitcoin\'s peer-to-peer network, and quantify the resources involved in our attack via probabilistic analysis, Monte Carlo simulations, measurements and experiments with live bitcoin nodes. Finally, we present countermeasures, inspired by botnet architectures, that are designed to raise the bar for eclipse attacks while preserving the openness and decentralization of bitcoin\'s current network architecture.





2015-03-20
20:19 [Job][New] Visiting assistant professor, Department of Mathematical Sciences, University of Cincinnati

  The Department of Mathematical Sciences at the University of Cincinnati is seeking applicants for several Visiting Assistant Professorships in mathematics or statistics. Appointments will begin on August 15th, 2015 and will initially be for one year, with the possibility of renewal for a second year. Teaching load will nominally be two (3-4 credit) undergraduate courses per semester. Candidates must have a PhD in mathematics or statistics by the start date. The Department of Mathematical Sciences is dedicated to excellence in both research and teaching. The department has a graduate program offering MS and PhD degrees in mathematics and statistics. The department is looking for candidates with high-quality teaching and research and a strong potential for collaboration in areas of expertise of current faculty including cryptography, in particular, post-quantum cryptography. If you are interested, please apply immediately and contact: dingji (at) ucmail.uc.edu.

20:18 [Job][New] Marie Sklodowska-Curie Research Fellows in Cryptography (Early Stage Researchers – 2 posts), University of Bristol

  ECRYPT-NET is a research network of 6 universities and 2 companies that intends to develop advanced cryptographic techniques for the Internet of Things and the Cloud and to create efficient and secure implementations of those techniques on a broad range of platforms. ECRYPT-NET is funded by a prestigious Marie Sk?odowska-Curie ITN (Integrated Training Network) grant. The network will educate a group of 15 PhD students with a set of interdisciplinary skills in the areas of mathematics, computer science and electrical engineering. The training will be provided in an international context,that includes Summer Schools, workshops, internships, and complementary skills. Participants are expected to spend at least 6 months abroad in a network partner or in one of the 7 associated companies. We are looking for highly motivated candidates with a strong academic track record, ideally with some background on cryptology and with proven research abilities.

We offer an exciting working environment in an international network with top scientists that is geared towards cutting-edge research. The financial conditions are very attractive. The project offers an opportunity to travel and interact with other PhD students and scientists all over Europe. Candidates may have resided in the host country for a most 1 year in the 3 years preceding the application. They can have at most 2 years of research experience at the doctoral level.

The Cryptography and Information Security Group at Bristol are offering two ESR positions:

1) Leakage Resilience From Lattices:

2) MPC using FHE and Oblivious Transfer:

Marie Curie ITN eligibility criteria apply to both of these positions.



09:17 [Pub][ePrint] Quadratic Time, Linear Space Algorithms for Gram-Schmidt Orthogonalization and Gaussian Sampling in Structured Lattices, by Vadim Lyubashevsky and Thomas Prest

  A procedure for sampling lattice vectors is at the heart of many lattice constructions, and the algorithm of Klein (SODA 2000) and Gentry, Peikert, Vaikuntanathan (STOC 2008) is currently the one that produces the shortest vectors. But due to the fact that its most time-efficient (quadratic-time) variant requires the storage of the Gram-Schmidt basis, the asymptotic space requirements of this algorithm are the same for general and ideal lattices. The main result of the current work is a series of algorithms that ultimately lead to a sampling procedure producing the same outputs as the Klein/GPV one, but requiring only linear-storage when working on lattices used in ideal-lattice cryptography. The reduced storage directly leads to a reduction in key-sizes by a factor of $\\Omega(d)$, and makes cryptographic constructions requiring lattice sampling much more suitable for practical applications.

At the core of our improvements is a new, faster algorithm for computing the Gram-Schmidt orthogonalization of a set of vectors that are related via a linear isometry. In particular, for a linear isometry r:R^d --> R^d which is computable in time $O(d)$ and a d-dimensional vector $b$, our algorithm for computing the orthogonalization of $(b,r(b),r^2(b),...,r^{d-1}(b))$ uses $O(d^2)$ floating point operations. This is in contrast to $O(d^3)$ such operations that are required by the standard Gram-Schmidt algorithm. This improvement is directly applicable to bases that appear in ideal-lattice cryptography because those bases exhibit such ``isometric structure\'\'. The above-mentioned algorithm improves on a previous one of Gama, Howgrave-Graham, Nguyen (EUROCRYPT 2006) which used different techniques to achieve only a constant-factor speed-up for similar lattice bases. Interestingly, our present ideas can be combined with those from Gama et al. to achieve an even an larger practical speed-up.

We next show how this new Gram-Schmidt algorithm can be applied towards lattice sampling in quadratic time using only linear space. The main idea is that rather than pre-computing and storing the Gram-Schmidt vectors, one can compute them ``on-the-fly\'\' while running the sampling algorithm. We also rigorously analyze the required arithmetic precision necessary for achieving negligible statistical distance between the outputs of our sampling algorithm and the desired Gaussian distribution. The results of our experiments involving NTRU lattices show that the practical performance improvements of our algorithms are as predicted in theory.