Threshold implementation is a method based on secret sharing to secure cryptographic ciphers (and in particular S-boxes) against differential power analysis side-channel attacks which was proposed by Nikova, Rechberger, and Rijmen in 2006. Until now, threshold implementations were only constructed for specific types of functions and some small S-boxes, but no generic construction was ever presented. In this paper, we present the first universal threshold implementation with$t+2$shares that is applicable to any bijective S-box, where$t$is its algebraic degree (or is larger than the algebraic degree). While being universal, our construction is also optimal with respect to the number of shares, since the theoretically smallest possible number,$t+1$, is not attainable for some bijective S-boxes. Our results enable low latency secure hardware implementations without the need for additional randomness. In particular, we apply this result to find two uniform sharings of the AES S-box. The first sharing is obtained by using the threshold implementation of the inversion in$\mathbb {F}_{2^{8}}$and the second by using two threshold implementations of two cubic power permutations that decompose the inversion. Area and performance figures for hardware implementations are provided.

Abstract Automated search methods based on Satisfiability Modulo Theory (SMT) problems are being widely used to evaluate the security of block ciphers against distinguishing attacks. While these methods provide a systematic and generic methodology, most of their software implementations are limited to a small set of ciphers and attacks, and extending these implementations requires significant effort and expertise. In this work, the authors present cryptographic algorithms for distinguishing attacks ( CASCADA ), an open‐source Python library to evaluate the security of cryptographic primitives, specially block ciphers, against distinguishing attacks with bit‐vector SMT solvers. The tool CASCADA implements the bit‐vector property framework herein proposed and several SMT‐based automated search methods to evaluate the security of ciphers against differential, related‐key differential, rotational‐XOR, impossible‐differential, impossible‐rotational‐XOR, related‐key impossible‐differential, linear and zero‐correlation cryptanalysis. The library CASCADA is the result of a huge engineering effort, and it provides many functionalities, a modular design, an extensive documentation and a complete suite of tests.

In this workshop, we focus on physical attacks and their countermeasures. With the advent of the Internet of Things, the interest in embedded cryptographic systems and physical attacks on these systems is steadily increasing, both in academia and industry. Sophisticated security certification and evaluation methods have been established to give assurance about the security claims by independent evaluation and testing. The certification has a drawback that it is time consuming and expensive. There is a need for further developing provably secure protection methods and automated verification tools, but also improving the efficiency and quality of certification by integrating these tools and methods. All these challenges motivate even more research on the Theory of Implementation Security.

In this study, the authors propose an accurate approach to model the propagation of the division property of linear layers by the smallest amount of inequalities. The solutions of the inequalities are exactly the division trails of a linear transformation. Therefore, the description is compact and optimal. As applications of their results, they present a 7‐round integral distinguisher for both Midori64 and Midori128. The designers of Midori only obtained a 3.5‐round integral characteristic. For Skinny64, they find a 10‐round integral distinguisher which was previously found by the designers. It is well to remind that their result proves that 7 rounds and 10 rounds are the upper bounds of Midori and Skinny64 correspondingly when searching for integral distinguishers based on division property. The significance of their result lies in that they shed light on how far division cryptanalysis can influence the security analysis of block ciphers with a binary diffusion layer, and their technique can be used to prove security against division cryptanalysis.

Recently the CAESAR competition has announced several finalists among the submitted authenticated encryption algorithms, after an open selection process during the last 5 years. Applications using these algorithms are rapidly increasing today. Devices implementing these applications are enormously susceptible to physical attacks, which are able to retrieve secret data through side-channel information such as the power consumption or the electromagnetic radiations. In this work we present a Side-Channel Analysis resistant hardware implementation of the whole family of authenticated encryption schemes Ketje. By changing just one parameter, any of the Ketje designs can be obtained, and tailored for different applications, either lightweight or high throughput. We introduce a new protected Keccak implementation, as well as unprotected and protected Ketje implementations, which allow both encryption and decryption modes in the same module. In order to secure these implementations we make use of the masking scheme known as Threshold Implementations and complement it with the technique of "Changing of the Guards", achieving a first-order Side-Channel Analysis protected implementation with zero extra randomness needed. This way, no dedicated PRNG needs to be additionally implemented, avoiding issues such as the security of the PRNG itself or the quality of the randomness.

In this study, the authors generalise Hadamard matrix over and propose a new form of Hadamard matrix, which they call generalised Hadamard (GHadamard) matrix. Then, they focus on generating lightweight (involutory) maximum distance separable (MDS) matrices. They also extend this idea to any matrix form, where k is not necessarily a power of 2. The new matrix form, GHadamard matrix, is used to generate new involutory MDS matrices over and , and involutory/non‐involutory MDS matrices over by considering the minimum exclusive OR (XOR) count, which is a metric defined to estimate the hardware implementation cost. In this context, they improve the best‐known results of XOR counts for involutory/non‐involutory MDS matrices over .

In this study, the authors propose new methods using a divide‐and‐conquer strategy to generate n × n binary matrices (for composite n ) with a high/maximum branch number and the same Hamming weight in each row and column. They introduce new types of binary matrices: namely, ( BHwC ) t , m and ( BCwC ) q , m types, which are a combination of Hadamard and circulant matrices, and the recursive use of circulant matrices, respectively. With the help of these hybrid structures, the search space to generate a binary matrix with a high/maximum branch number is drastically reduced. By using the proposed methods, they focus on generating 12 × 12, 16 × 16 and 32 × 32 binary matrices with a maximum or maximum achievable branch number and the lowest implementation costs (to the best of their knowledge) to be used in block ciphers. Then, they discuss the implementation properties of binary matrices generated and present experimental results for binary matrices in these sizes. Finally, they apply the proposed methods to larger sizes, i.e. 48 × 48, 64 × 64 and 80 × 80 binary matrices having some applications in secure multi‐party computation and fully homomorphic encryption.

The Internet of Things (IoT) enables a network of communication between people-to-people, people-to-things and things-to-things. The security of these communications against all possible attacks is a significant part of todays security and privacy. Due to the design nature of IoT systems, IoT devices are easily accessible by attackers which increases the importance of their security against physical attacks. This workshop is dedicated to research on the design of cryptographic algorithms and implementations secure against physical attacks.

SIMON is a new family of lightweight block ciphers proposed by the National Security Agency (NSA) in 2013. Since its publication, it has attracted much research interest and a number of analysis results have been presented. As a popular kind of implementation attack method, the fault attack also works when it is applied to SIMON. In this paper, we propose an effective fault attack on SIMON under the random byte fault model. Compared with the previous attack results, our attack can successfully recover the whole master key with injecting the faults into only one intermediate round for six instances of SIMON. In our attack, we fully utilize a class of differential propagation properties of SIMON to determine the fault injection position as long as the full diffusion of the fault has not been obtained. On the basis of it, we can recover the last round key with the differential analysis technique. The differential propagation properties make it possible to inject the faults into the earlier intermediate round at the beginning than that of the previous attacks. Meanwhile, the same faulty ciphertext set can also help to recover other round keys. So we do not have to inject the faults into any other intermediate rounds to reveal the whole master key. Moreover, in this paper we also give a detailed mathematical analysis on the average number of the fault injections under the random byte fault model. The data complexity analysis shows that less fault injections are required in our attack compared with other work under the same attack model. Finally, we also verify the effectiveness and correctness of our attack with experiments.

Embedded cryptographic devices are vulnerable to power analysis attacks. Threshold implementations (TIs) provide provable security against first-order power analysis attacks for hardware and software implementations. Like masking, the approach relies on secret sharing but it differs in the implementation of logic functions. While masking can fail to provide protection due to glitches in the circuit, TIs rely on few assumptions about the hardware and are fully compatible with standard design flows. We investigate two important properties of TIs in detail and point out interesting trade-offs between circuit area and randomness requirements. We propose two new TIs of AES that, starting from a common previously published implementation, illustrate possible trade-offs. We provide concrete ASIC implementation results for all three designs using the same library, and we evaluate the practical security of all three designs on the same FPGA platform. Our analysis allow us to directly compare the security provided by the different trade-offs, and to quantify the associated hardware cost.

The majority of current attacks on reduced-round variants of block ciphers seeks to maximize the number of rounds that can be broken, using less data than the entire codebook and less time than exhaustive key search. In this paper, we pursue a different approach, restricting the data available to the adversary to a few plaintext/ciphertext pairs. We argue that consideration of such attacks (which received little attention in recent years) improves our understanding of the security of block ciphers and of other cryptographic primitives based on block ciphers. In particular, these attacks can be leveraged to more complex attacks, either on the block cipher itself or on other primitives (e.g., stream ciphers, MACs, or hash functions) that use a small number of rounds of the block cipher as one of their components. As a case study, we consider the Advanced Encryption Standard (AES)-the most widely used block cipher. The AES round function is used in many cryptographic primitives, such as the hash functions Lane, SHAvite-3, and Vortex or the message authentication codes ALPHA-MAC, Pelican, and Marvin. We present attacks on up to four rounds of AES that require at most three known/chosen plaintexts. We then apply these attacks to cryptanalyze an AES-based stream cipher (which follows the leak extraction methodology), and to mount the best known plaintext attack on six-round AES.

A new cryptographic hash function Whirlwind is presented. We give the full specification and explain the design rationale. We show how the hash function can be implemented efficiently in software and give first performance numbers. A detailed analysis of the security against state-of-the-art cryptanalysis methods is also provided. In comparison to the algorithms submitted to the SHA-3 competition, Whirlwind takes recent developments in cryptanalysis into account by design. Even though software performance is not outstanding, it compares favourably with the 512-bit versions of SHA-3 candidates such as LANE or the original CubeHash proposal and is about on par with ECHO and MD6.

The authors present three security claims for iterated message authentication codes (MAC functions). Next, they propose ALRED, a construction method for MAC functions based on a block cipher that has provable security in the absence of internal collisions. They apply this construction to advanced encryption standard (AES) resulting in two MAC functions: ALPHA-MAC and PELICAN. The authors provide a model for describing different types of internal collisions in ALRED and provide evidence that the security claims they propose are usable for MAC functions that use the ALRED construction. Finally, they provide a motivation for the security claims that accompany PELICAN.

In this study, the authors analyse with respect to algebraic attacks a small-scale version of the stream cipher Lex. They base it on a small-scale version of the block cipher advanced encryption standard (AES) with 16-bit state and 16-bit key. They represent the small-scale Lex and its key schedule in two alternative ways: as a system of cubic boolean equations and as a system of quadratic boolean equations. The authors use Gröbner bases to solve the two systems for different number of rounds and sizes of the leak. They obtain the best results for the quadratic representation of the cipher. For this case they are able to recover the secret key in time less than 2 min by solving a system of 374 quadratic boolean equations in 208 unknowns resulting from 5 rounds of the cipher.

The hash function design strategy SMASH was recently proposed as an alternative to the MD4 family of hash functions. It can be shown that the strategy leads to designs that are vulnerable to efficient collision and (second) preimage attacks. The mathematical structure of the SMASH description facilitates the description of the weakness and the resulting attacks, but also functions with less mathematical elegance may show similar weaknesses.

Plateau characteristics are a special type of characteristics whose probability depends on the key and can have only two values. For a (usually small) subset of the keys it has a non-zero probability and for all other keys its probability is zero. For a large group of ciphers, including the AES, all two-round characteristics are plateau characteristics. For the AES and other ciphers with a similar structure, the vast majority of characteristics over four or more rounds are plateau characteristics. In the case of the AES, for most keys, there are two-round characteristics with fixed-key probability equal to 32/232, whereas the maximum expected differential probability of two-round differentials is at most 13.25/232.

Recent breakthroughs in cryptanalysis of standard hash functions like SHA-1 and MD5 raise the need for alternatives. A credible alternative to for instance SHA-1 or the SHA-2 family of hash functions is Whirlpool. Whirlpool is a hash function that has been evaluated and approved by NESSIE and is standardized by ISO/IEC. To the best of our knowledge only one FPGA implementation of Whirlpool has been published to date. This implementation is designed for high throughput rates requiring a considerable amount of hardware resources. In this article we present a compact hardware implementation of the hash function Whirlpool. The proposed architecture uses an innovative state representation that makes it possible to reduce the required hardware resources remarkably. The complete implementation requires 1456 CLB-slices and, most notably, no block RAMs.

In this paper, we describe some weaknesses of public-key blockwise fragile authentication watermarkings and the means to make them secure. Wong's (1998) original algorithm is not secure against a mere block cut-and-paste or the well-known birthday attack. To make it secure, some schemes have been proposed to make the signature of each block depend on the contents of its neighboring blocks. We attempt to maximize the change localization resolution using only one dependency per block with a scheme we call hash block chaining version 1 (HBC1). We then show that HBC1, as well as any neighbor-dependent scheme, are susceptible to another forgery technique that we have named a transplantation attack. We also show a new kind of birthday attack that can be effectively mounted against HBC1. To thwart these attacks, we propose using a nondeterministic digital signature together with a signature dependent scheme (HBC2). Finally, we discuss the advantages of using discrete logarithm signatures instead of RSA for watermarking.