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16:33 [Job][New] Ph.D. student or Post-Doc (cryptographic protocols and/or electronic voting), University of Trier, Germany

  The Chair for Information Security and Cryptography at University of Trier, Germany, offers a full-time PhD/Postdoc position.

The position involves both research and teaching in the area of cryptography/information security. The successful candidate is expected to contribute to research in cryptographic protocols and/or electronic voting.

The position is available immediately and is fully funded, with an internationally competitive salary.

Contracts are initially offered for two years. An extension to a total duration of up to six years is possible.

He or she is given the possibility to carry out a Ph.D. or, for Postdocs, a Habilitation.

The successful candidate should have a Master\'s degree or a Ph.D. (or should be very close to completion thereof) in Computer Science, Mathematics, Information Security, or a related field, with strong analytical and mathematical skills. Knowledge in cryptography is an asset. Since teaching is mostly done in German, sufficient knowledge of German is required.

The deadline for applications is October 5th, 2014. However, late applications will be considered until the position is filled.

See for the official job announcement (in German).

15:17 [Pub][ePrint] A Unified Formalism for Physical Attacks, by Hélène Le Bouder , Ronan Lashermes , Yanis Linge , Bruno Robisson and Assia Tria

  The security of cryptographic algorithms can be consideredin two contexts. On the one hand, these algorithms can be proven secure mathematically. On the other hand, physical attacks can weaken the implementation of an algorithm yet proven secure. Under the common name of physical attacks, different attacks are regrouped: side channel

attacks and fault injection attacks. This paper presents a common formalism for these attacks and highlights their underlying principles. All physical attacks on symmetric algorithms can be described with a 3-step process. Moreover it is possible to compare different physical attacks, by separating the theoretical attack path and the experimental parts of the attacks.

15:17 [Pub][ePrint] Error-Tolerant Algebraic Side-Channel Attacks Using BEE, by Ling Song and Lei Hu and Siwei Sun and Zhang Zhang and Danping Shi and Ronglin Hao

  Algebraic side-channel attacks are a type of side-channel analysis which can recover the secret information with a small number of samples (e.g., power traces). However, this type of side-channel analysis is sensitive to measurement errors which may make the attacks fail.

In this paper, we propose a new method of algebraic side-channel attacks which considers noisy leakages as integers restricted to intervls and finds out the secret information with a constraint programming solver named BEE. To demonstrate the efficiency of this new method in algebraic side-channel attacks, we analyze some popular implementations of block ciphers---PRESENT, AES, and SIMON under the Hamming weight or Hamming distance leakage model. For AES, our method requires the least leakages compared with existing works under the same error model. For both PRESENT and SIMON, we provide the first analytical results of them under algebraic side-channel attacks in the presence of errors. To further demonstrate the wide applicability of this new method, we also extend it to cold boot attacks. In the cold boot attacks against AES, our method increases the success rate by over $25\\%$ than previous works.

15:17 [Pub][ePrint] Towards a Full-Featured Implementation of Attribute Based Credentials on Smart Cards, by Antonio de la Piedra, Jaap-Henk Hoepman, Pim Vullers

  Attribute-based Credentials (ABCs) allow citizens to prove certain properties about themselves without necessarily revealing their full identity. Smart cards are an attractive container for such credentials, for security and privacy reasons. But their limited processing power and random access storage capacity pose a severe challenge. Recently, we, the IRMA team, managed to fully implement a limited subset of the Idemix ABC system on a smart card, with acceptable running times. In this paper we extend this functionality by overcoming the main hurdle: limited RAM. We implement an efficient

extended Pseudo-Random Number Generator (PRNG) for recomputing pseudorandomness and reconstructing variables. Using this we implement Idemix standard and domain pseudonyms, AND proofs based on prime-encoded attributes, and equality proofs of representation modulo a composite, together with terminal verification and secure messaging. In contrast to prior work that only addressed the verification of one credential with only one attribute (particularly, the master secret), we can now perform multi-credential proofs on credentials of 5 attributes and complex proofs in reasonable time. We provide a detailed performance analysis and compare our results to other approaches.

15:17 [Pub][ePrint] A Counterexample to the Chain Rule for Conditional HILL Entropy, by Stephan Krenn and Krzysztof Pietrzak and Akshay Wadia and Daniel Wichs

  Most entropy notions $H(.)$ like Shannon or min-entropy satisfy a chain rule stating that for random variables $X,Z$ and $A$ we have $H(X|Z,A)\\ge H(X|Z)-|A|$. That is, by conditioning on $A$ the entropy of $X$ can decrease by at most the bitlength $|A|$ of $A$.

Such chain rules are known to hold for some computational entropy notions like

Yao\'s and unpredictability-entropy. For HILL entropy, the computational analogue of

min-entropy, the chain rule is of special interest and has found many applications, including leakage-resilient cryptography, deterministic encryption and memory delegation.

These applications rely on restricted special cases of the chain rule. Whether the chain rule for conditional HILL entropy holds in general was an open problem for which we give a strong negative answer: We construct joint distributions $(X,Z,A)$, where $A$ is a

distribution over a \\emph{single} bit, such that the HILL entropy $H_\\infty(X|Z)$ is

large but $H_\\infty(X|Z,A)$ is basically zero.

Our counterexample just makes the minimal assumption that

${\\bf NP}\\nsubseteq{\\bf P/poly}$. Under the stronger assumption that

injective one-way function exist, we can make all the distributions efficiently samplable.

Finally, we show that some more sophisticated cryptographic objects

like lossy functions can be used to sample a distribution constituting a counterexample to the chain rule making only a single invocation to the underlying object.

15:17 [Pub][ePrint] Remarks on the Cryptographic Primitive of Attribute-based Encryption, by Zhengjun Cao and Lihua Liu

  Attribute-based encryption (ABE) which allows users to encrypt and decrypt messages based on user attributes is a type of one-to-many encryption. Unlike the conventional one-to-one encryption which has no intention to exclude any partners of the intended receiver from obtaining the plaintext, an ABE system tries to exclude some unintended recipients from obtaining the plaintext whether they are partners of some intended recipients. We remark that this requirement for ABE is very hard to meet. An ABE system cannot truly exclude some unintended recipients from decryption because some users can exchange their decryption keys in order to maximize their own interests. The flaw discounts the importance of the cryptographic primitive.

15:17 [Pub][ePrint] Improved Linear Cryptanalysis of Round Reduced SIMON, by Javad Alizadeh, Hoda A. Alkhzaimi, Mohammad Reza Aref, Nasour Bagheri, Praveen Gauravaram and Martin M. Lauridsen

  SIMON is a family of ten lightweight block ciphers published by Beaulieu et al. from U.S. National Security Agency (NSA). A cipher in this family with $K$-bit key and $N$-bit block is called SIMON ${N}/{K}$. In this paper we investigate the security of SIMON against different variants of linear cryptanalysis, i.e., classic linear, multiple linear and linear hull attacks. We present a connection between linear characteristic and differential characteristic, multiple linear and differential and linear hull and differential, and employ it to adapt the current known results on differential cryptanalysis of SIMON to linear cryptanalysis of this block cipher. Our best linear cryptanalysis covers SIMON 32/64 reduced to 20 rounds out of 32 rounds with the

data complexity $2^{31.69}$ and time complexity $2^{59.69}$. We have implemented our attacks for small scale variants of SIMON and our experiments confirm the theoretical bias presented in this work. So far, our results are the best known with respect to linear cryptanalysis for any variant of SIMON.

18:17 [Pub][ePrint] Attacks in Stream Ciphers: A Survey, by Gustavo Banegas

  Nowadays there are different types of attacks in block and stream ciphers. In this work we will present some

of the most used attacks on stream ciphers. We will present the newest techniques with an example of usage in

a cipher, explain and comment. Previous we will explain the difference between the block ciphers and stream


15:17 [Pub][ePrint] Fully Collusion-Resistant Traceable Key-Policy Attribute-Based Encryption with Sub-linear Size Ciphertexts, by Zhen Liu and Zhenfu Cao and Duncan S. Wong

  Recently a series of expressive, secure and efficient Attribute-Based Encryption (ABE) schemes, both in key-policy flavor and ciphertext-policy flavor, have been proposed.

However, before being applied into practice, these systems have to attain traceability of malicious users.

As the decryption privilege of a decryption key in Key-Policy ABE (resp. Ciphertext-Policy ABE) may be shared by multiple users who own the same access policy (resp. attribute set), malicious users might tempt to leak their decryption privileges to third parties, for financial gain as an example, if there is no tracing mechanism for tracking them down.

In this work we study the traceability notion in the setting of Key-Policy ABE, and formalize Key-Policy ABE supporting fully collusion-resistant blackbox traceability. An adversary is allowed to access an arbitrary number of keys of its own choice when building a decryption-device, and given such a decryption-device while the underlying decryption algorithm or key may not be given, a Blackbox tracing algorithm can find out at least one of the malicious users whose keys have been used for building the decryption-device.

We propose a construction, which supports both fully collusion-resistant blackbox traceability and high expressiveness (i.e. supporting any monotonic access structures). The construction

is fully secure in the standard model (i.e. it achieves the best security level that the conventional non-traceable ABE systems do to date), and

is efficient that the fully collusion-resistant blackbox traceability is attained at the price of making ciphertexts grow only sub-linearly in the number of users in the system, which is the most efficient level to date.

12:17 [Pub][ePrint] The Usage of Counter Revisited: Second-Preimage Attack on New Russian Standardized Hash Function, by Jian Guo and Jérémy Jean and Gaëtan Leurent and Thomas Peyrin and Lei Wang

  Streebog is a new Russian hash function standard. It follows the HAIFA

framework as domain extension algorithm and claims to resist recent generic

second-preimage attacks with long messages. However, we demonstrate in this

article that the specific instantiation of the HAIFA framework used in Streebog

makes it weak against such attacks. More precisely, we observe that Streebog

makes a rather poor usage of the HAIFA counter input in the compression

function, which allows to construct second-preimages on the full Streebog-512

with a complexity as low as 2^{266} compression function evaluations for long

messages. This complexity has to be compared with the expected 2^{512}

computations bound that an ideal hash function should provide. Our work is a

good example that one must be careful when using a design framework for which

not all instances are secure. HAIFA helps designers to build a secure hash

function, but one should pay attention to the way the counter is handled inside

the compression function.

00:17 [Pub][ePrint] SCORAM: Oblivious RAM for Secure Computation, by Xiao Shaun Wang and Yan Huang and T-H. Hubert Chan and abhi shelat and Elaine Shi

  Oblivious RAMs (ORAMs) have traditionally been measured by their \\emph{bandwidth overhead} and \\emph{client storage}. We observe that when using ORAMs to build secure computation protocols for RAM programs, the \\emph{size} of the ORAM circuits is more relevant to the performance.

We therefore embark on a study of the \\emph{circuit-complexity} of several recently proposed ORAM constructions. Our careful implementation and experiments show that asymptotic analysis is not indicative of the true performance of ORAM in secure computation protocols with practical data sizes.

We then present SCORAM, a heuristic \\emph{compact} ORAM design optimized for secure computation protocols. Our new design is almost 10x smaller in circuit size and also faster than all other designs we have tested for realistic settings (i.e., memory sizes between 4MB and 2GB, constrained by $2^{-80}$ failure probability). SCORAM\\ makes it feasible to perform secure computations on gigabyte-sized data sets.