International Association
for Cryptologic Research

3 PhD Fellowships in the area of hardware Security. A strong background in VLSI Design, Nano-electronics. VLSI Testing, Reliability, Security. Highly competitive, 4-year guaranteed fellowships are available.

We propose a tool for automatic search for differential trails in ARX ciphers. By introducing the concept of a partial difference distribution table (pDDT) we extend Matsui\'s algorithm, originally proposed for DES-like ciphers, to the class of ARX ciphers. To the best of our knowledge this is the first application of Matsui\'s algorithm to ciphers that do not have S-boxes. The tool is applied to the block ciphers TEA, XTEA, SPECK and RAIDEN. For RAIDEN we find an iterative characteristic on all 32 rounds that can be used to break the full cipher using standard differential cryptanalysis. This is the first cryptanalysis of the cipher in a non-related key setting. Differential trails on 9, 10 and 13 rounds are found for SPECK32, SPECK48 and SPECK64 respectively. The 13 round trail covers half of the total number of rounds. These are the first public results on the security analysis of SPECK. For TEA multiple full (i.e. not truncated) differential trails are reported for the first time, while for XTEA we confirm the previous best known trail reported by Hong et al. We also show closed formulas for computing the exact additive differential probabilities of the left and right shift operations. The source code of the tool is publicly available as part of a larger toolkit for the analysis of ARX at the following address: https://github.com/vesselinux/yaarx .

Reducing the entropy of the mask is a technique which has been proposed to mitigate the high performance overhead of masked software implementations of symmetric block ciphers. Rotating S-box Masking (RSM) is an example of such schemes applied to AES with the purpose of maintaining the security at least against univariate first-order side-channel attacks. This article examines the vulnerability of a realization of such technique using the side-channel measurements publicly available through DPA contest V4. Our analyses which focus on exploiting the first-order leakage of the implementation discover a couple of potential attacks which can recover the secret key. Indeed the leakage we exploit is due to a design mistake as well as the characteristics of the implementation platform, none of which has been considered during the design of the countermeasure (implemented in naive C code).

The famous Goldbach\'s conjecture and Polignac\'s conjecture are two of all unsolved problems in the field of number theory today. As well known, the Goldbach\'s conjecture and the Polignac\'s conjecture are equivalent. Most of the literatures does not introduce about internal equivalence in Polignac\'s conjecture. In this paper, we would like to discuss the internal equivalence to the Polignac\'s conjecture, say $T_{2k}(x)$ and $T(x)$ are equivalent. Since $T_{2k}\\sim T(x)\\sim 2c\\cdot \\frac{x}{(\\ln x)^{2}}$, we rewrite and re-express to $T(x)\\sim T_{4}(x)\\sim T_{8}(x)\\sim T_{16}(x)\\sim T_{32}(x)\\sim T_{2^{n}}(x)\\sim 2c\\cdot \\frac{x}{(\\ln x)^{2}}$. And then connected with the Goldbach\'s conjecture. Finally, we will point out the important prime number symmetry role of play in these two conjectures.

At Eurocrypt 2011, Wee presented a generalization of threshold public key encryption, threshold signatures, and revocation schemes arising from threshold extractable hash proof systems. In particular, he gave instances of his generic revocation scheme from the DDH assumption (which led to the Naor-Pinkas revocation scheme), and from the factoring assumption (which led to a new revocation scheme). We expand on Wee\'s work in two directions:

(a) We propose threshold extractable hash proof instantiations from the \"Extended Decisional Diffie-Hellman\" (EDDH) assumption due to Hemenway and Ostrovsky (PKC 2012). This in particular yields EDDH-based variants of threshold public key encryption, threshold signatures, and revocation schemes. In detail, this yields a DCR-based revocation scheme.

(b) We show that our EDDH-based revocation scheme allows for a mild form of traitor tracing (and, thus, yields a new trace-and-revoke scheme). In particular, compared to Wee\'s factoring-based scheme, our DCR-based scheme has the advantage that it allows to trace traitors.

How is it possible to prevent the sharing of cryptographic

functions? This question appears to be fundamentally hard to address

since in this setting the owner of the key {\\em is} the adversary:

she wishes to share a program or device that (potentially only

partly) implements her main cryptographic functionality. Given that

she possesses the cryptographic key, it is impossible for her to be

{\\em prevented} from writing code or building a device that uses

that key. She may though be {\\em deterred} from doing so.

We introduce {\\em leakage-deterring} public-key cryptographic

primitives to address this problem. Such primitives have the feature

of enabling the embedding of owner-specific private data into the

owner\'s public-key so that given access to {\\em any} (even

partially functional) implementation of the primitive, the recovery

of the data can be facilitated. We formalize the notion of

leakage-deterring in the context of encryption, signature, and

identification and we provide efficient generic constructions that

facilitate the recoverability of the hidden data while retaining

privacy as long as no sharing takes place.

In this paper, we consider an RSA modulus $N=pq$, where the prime factors $p$, $q$ are of the same size. We present an attack on RSA when the decryption exponent $d$ is in the form $d=Md_1+d_0$ where $M$ is a given positive integer and $d_1$ and $d_0$ are two suitably small unknown integers. In 1999, Boneh and Durfee~\\cite{BODU} presented an attack on RSA when $d

RFID (Radio Frequency Identification) is one of the most growing technologies among the pervasive systems. Non line of sight capability makes RFID systems much faster than its other contending systems such as barcodes and magnetic taps etc. But there are some allied security apprehensions with RFID systems. RFID security has been acquired a lot of attention in last few years as evinced by the large number of publications (over 2000).

In this paper, a brief survey of eminent ultralightweight authentication protocols has been presented & then a four-layer security model, which comprises of various passive and active attacks, has been proposed. Cryptanalysis of these protocols has also been performed under the implications of the proposed security model

Key agreement allows multi-parties exchanging public information to create a common secret key that is known only to those entities over an insecure network. In recent years, several identity-based authenticated key agreement protocols have been proposed. In this study, we analyze three identity-based tripartite authenticated key agreement protocols.

After the analysis, we found that these protocols do not possess the desirable security attributes.

Profiling power attacks like Template attack and Stochastic attack optimize their performance by jointly evaluating the leakages of multiple sample points. However, such multivariate approaches are rare among non-profiling Differential Power Analysis (DPA) attacks, since integration of the leakage of a higher SNR sample point with the leakage of lower SNR sample point might result in a decrease in the overall performance. One of the few successful multivariate approaches is the application of Principal Component Analysis (PCA) for non-profiling DPA. However, PCA also performs sub-optimally in the presence of high noise. In this paper, a multivariate model for an FPGA platform is introduced for improving the performances of non-profiling DPA attacks. The introduction of the proposed model

greatly increases the success rate of DPA attacks in the presence of high noise. The experimental results on both simulated power traces and real power traces are also provided as an evidence.

In this paper we show that it is possible and, indeed, feasible to use secure multiparty computation for calculating the probability of a collision between two satellites. For this purpose, we first describe basic floating-point arithmetic operators (addition and multiplication) for multiparty computations. The operators are implemented on the SHAREMIND secure multiparty computation engine. We discuss the implementation details, provide methods for evaluating example elementary functions (inverse, square root, exponentiation of e, error function). Using these primitives, we implement a satellite conjunction analysis algorithm and give benchmark results for the primitives as well as the conjunction analysis itself.

This paper discusses combined modeling and side

channel attacks on Strong Physical Unclonable Functions (Strong

PUFs). We illustrate our method by the example of the two

currently most secure (CCS 2010, IEEE T-IFS 2013) electrical

Strong PUFs, so-called XOR Arbiter PUFs and Lightweight

PUFs, and successfully attack them at sizes and complexities

far beyond the reach of pure modeling techniques (CCS 2010,

IEEE T-IFS 2013).

Our approach makes use of the first power and timing

side channels on PUFs reported in the literature. Both provide

information on the single outputs of the many parallel Arbiter

PUFs inside an XOR Arbiter PUF or Lightweight PUF, and

indicate how many of these single outputs (in sum) were equal

to one (and how many were equal to zero) before they entered

the final XOR gate. Taken for itself, this side channel information

is of little value. But if combined with suitably adapted machine

learning techniques, it substantially changes attack performance:

It reduces the empirically estimated complexities for modeling the

above two PUFs from exponential (CCS 2010, IEEE T-IFS) to

low degree polynomial.

The practical viability of our attacks is firstly demonstrated

by SPICE simulations, and by subsequent ML experiments on

numerically simulated CRPs. We thereby confirm attacks on the

two above PUFs for up to 16 XORs and challenge bitlengths

of up to 512. Secondly, we execute a full experimental proof-ofconcept

for our timing side channel, successfully attacking FPGA implementations of the two above PUF types for 8, 12, and 16

XORs, and bitlengths 64, 128, 256 and 512. We implement these

sizes for the first time in the literature in silicon, and subsequently attack them successfully by our new methods. We remark that in recent works (CCS 2010, IEEE T-IFS 2013), 8 XOR architectures

with bitlength 512 had been explicitly suggested as secure and

beyond the reach of current attacks.

Finally, we discuss efficient countermeasures against our power

and timing side channels. They could and should be used to secure

future Arbiter PUF generations against the latter.

In this paper we study the security of hash functions SM3 and BLAKE-256 against boomerang attack. SM3 is designed by X. Wang et al. and published by Chinese Commercial Cryptography Administration Office for the use of electronic certification service system in China. BLAKE is one of the five finalists of the NIST SHA-3 competition submitted by J.-P. Aumasson et al. For SM3, we present boomerang distinguishers for the compression function reduced to 34/35/36/37/38 steps out of 64 steps, with time complexities $2^{31.4}$, $2^{33.6}$, $2^{73.4}$, $2^{93}$ and $2^{192}$ respectively. Then we show some incompatible problems existed in the previous boomerang attacks on SM3. Meanwhile, we launch boomerang attacks on up to 7 and 8 rounds keyed permutation of BLAKE-256 which are the first valid $7$-round and $8$-round boomerangs for BLAKE-256. Especially, since our distinguishers on 34/35-step compression function of SM3 and 7-round keyed permutation of BLAKE-256 are practical, we are able to obtain boomerang quartets of these attacks. As far as we know, these are the best results against round-reduced SM3 and BLAKE-256.

We construct an Identity-Based Key Encapsulation Mechanism (IB-KEM) in a generic \"leveled\" multilinear map setting and make it translated to the GGH framework, which defined an \"approximate\" version of a multilinear group family from ideal lattices. Then, we prove their security in the selective-ID model.

We present a new approach to the compression technique of Lyubashevsky et al for lattice-based signatures based on learning with errors (LWE).

Our ideas seem to be particularly suitable for signature schemes whose security, in the random oracle model, is based on standard worst-case computational assumptions. Our signatures are shorter than any previous proposal for provably-secure signatures based on standard lattice problems: at the 128-bit level we improve signature size from (more than) 16500 bits to around 9000 to 12000 bits.

We consider the binary-LWE problem, which is the learning with errors problem when the entries of the secret vector are chosen from $\\{ 0, 1\\}$ or $\\{ -1, 0, 1 \\}$ (and the error vector is sampled from a discrete Gaussian distribution). Our main result is an algorithm for binary-LWE that first translates the problem to the inhomogeneous short integer solution (ISIS) problem, and then solves the closest vector problem using a re-scaling of the lattice. We also discuss modulus switching as an approach to the problem. Our conclusions are that binary-LWE is easier than general LWE. We give experimental results that will be of help when choosing parameters for binary-LWE to achieve certain security levels.

We continue the line of work initiated by Katz (Eurocrypt 2007) on using tamper-proof hardware for universally composable secure computation. As our main result, we show an efficient oblivious-transfer (OT) protocol in which two parties each create and exchange a single, stateless token and can then run an unbounded number of OTs. Our result yields what we believe is the most practical and efficient known approach for oblivious transfer based on tamper-proof tokens, and implies that the parties can perform (repeated) secure computation of arbitrary functions without exchanging additional tokens.

Motivated by this result, we investigate the minimal number of stateless tokens needed for universally composable OT/secure computation. We prove that our protocol is optimal in this regard for constructions making black-box use of the tokens (in a sense we define). We also show that nonblack-box techniques can be used to obtain a construction using only a single stateless token.

The steadily growing number of certication authorities (CAs)

assigned to the Web Public Key Infrastructure (Web PKI) and trusted

by current browsers imposes severe security issues. Apart from being

impossible for relying entities to assess whom they actually trust, the

current binary trust model implemented with the Web PKI makes each

CA a single point of failure. In this paper, we present the concept of

trust views to manage variable trust levels for exactly those CAs actually

required by a relying entity. This reduces the set of trusted CAs

and minimizes the risk to rely on malicious certicates issued due to CA

failures or compromises.

Bitcoin has achieved large-scale acceptance and popularity by promising its users a low-cost, anonymous, and completely decentralized exchange of transactions. However, recent incidents and observations are revealing the true limits of decentralization in the Bitcoin system. In this article, we show that the vital operations and decisions that Bitcoin is currently undertaking are not decentralized. More specifically, we show that a limited set of entities currently control

the services, decision making, mining, and the incident resolution processes in Bitcoin. We also show that third-party entities can unilaterally decide to \"devalue\" any specific set of Bitcoin addresses pertaining to any entity participating in the system. Finally, we explore possible avenues to enhance the decentralization in the Bitcoin system.