Mixing Additive and Multiplicative Masking for Probing Secure Polynomial Evaluation Methods

International audienceMasking is a sound countermeasure to protect implementations of block-cipher algorithms against Side Channel Analysis (SCA). Currently, the most efficient masking schemes use Lagrange's Interpolation Theorem in order to represent any S-box by a polynomial function over a binary finite field. Masking the processing of an S-box is then achieved by masking every operation involved in the evaluation of its polynomial representation. While the common approach requires to use the well-known Ishai-Sahai-Wagner (ISW) scheme in order to secure this processing, there exist alternatives. In the particular case of power functions, Genelle, Prouff and Quisquater proposed an efficient masking scheme (GPQ). However, no generalization has been suggested for polynomial functions so far. In this paper, we solve the open problem of extending GPQ for polynomials, and we also solve the open problem of proving that both the original scheme and its variants for polynomials satisfy the t-SNI security definition. Our approach to extend GPQ is based on the cyclotomic method and results in an alternate cyclotomic method which is three times faster in practice than the original proposal in almost all scenarios we address. The best-known method for polynomial evaluation is currently CRV which requires to use the cyclotomic method for one of its step. We also show how to plug our alternate cyclo-tomic approach into CRV and again provide an alternate approach that outperforms the original in almost all scenarios. We consider the masking of n-bit S-boxes for n ∈ [4; 8] and we get in practice 35% improvement of efficiency for S-boxes with dimension n ∈ {5, 7, 8} and 25% for 6-bit S-boxes

AES Side-Channel Countermeasure using Random Tower Field Constructions

International audienceMasking schemes to secure AES implementations against side-channel attacks is a topic of ongoing research. The most sensitive part of the AES is the non-linear SubBytes operation, in particular, the inversion in GF(2^8), the Galois field of 2^8 elements. In hardware implementations, it is well known that the use of the tower of extensions GF(2) ⊂ GF(2^2) ⊂ GF(2^4) ⊂ GF(2^8) leads to a more efficient inversion. We propose to use a random isomorphism instead of a fixed one. Then, we study the effect of this randomization in terms of security and efficiency. Considering the field extension GF(2^8)/GF(2^4), the inverse operation leads to computation of its norm in GF(2^4). Hence, in order to thwart side-channel attack, we manage to spread the values of norms over GF(2^4). Combined with a technique of boolean masking in tower fields, our countermeasure strengthens resistance against first-order differential side-channel attacks

A new countermeasure against side-channel attacks based on hardware-software co-design

This paper aims at presenting a new countermeasure against Side-Channel Analysis (SCA) attacks, whose implementation is based on a hardware-software co-design. The hardware architecture consists of a microprocessor, which executes the algorithm using a false key, and a coprocessor that performs several operations that are necessary to retrieve the original text that was encrypted with the real key. The coprocessor hardly affects the power consumption of the device, so that any classical attack based on such power consumption would reveal a false key. Additionally, as the operations carried out by the coprocessor are performed in parallel with the microprocessor, the execution time devoted for encrypting a specific text is not affected by the proposed countermeasure. In order to verify the correctness of our proposal, the system was implemented on a Virtex 5 FPGA. Different SCA attacks were performed on several functions of AES algorithm. Experimental results show in all cases that the system is effectively protected by revealing a false encryption key.Peer ReviewedPreprin

Privately Connecting Mobility to Infectious Diseases via Applied Cryptography

Human mobility is undisputedly one of the critical factors in infectious disease dynamics. Until a few years ago, researchers had to rely on static data to model human mobility, which was then combined with a transmission model of a particular disease resulting in an epidemiological model. Recent works have consistently been showing that substituting the static mobility data with mobile phone data leads to significantly more accurate models. While prior studies have exclusively relied on a mobile network operator's subscribers' aggregated data, it may be preferable to contemplate aggregated mobility data of infected individuals only. Clearly, naively linking mobile phone data with infected individuals would massively intrude privacy. This research aims to develop a solution that reports the aggregated mobile phone location data of infected individuals while still maintaining compliance with privacy expectations. To achieve privacy, we use homomorphic encryption, zero-knowledge proof techniques, and differential privacy. Our protocol's open-source implementation can process eight million subscribers in one and a half hours. Additionally, we provide a legal analysis of our solution with regards to the EU General Data Protection Regulation.Comment: Added differentlial privacy experiments and new benchmark

Design of a Scan Chain for Side Channel Attacks on AES Cryptosystem for Improved Security

Scan chain-based attacks are side-channel attacks focusing on one of the most significant features of hardware test circuitry. A technique called Design for Testability (DfT) involves integrating certain testability components into a hardware design. However, this creates a side channel for cryptanalysis, providing crypto devices vulnerable to scan-based attacks. Advanced Encryption Standard (AES) has been proven as the most powerful and secure symmetric encryption algorithm announced by USA Government and it outperforms all other existing cryptographic algorithms. Furthermore, the on-chip implementation of private key algorithms like AES has faced scan-based side-channel attacks. With the aim of protecting the data for secure communication, a new hybrid pipelined AES algorithm with enhanced security features is implemented. This paper proposes testing an AES core with unpredictable response compaction and bit level-masking throughout the scan chain process. A bit-level scan flipflop focused on masking as a scan protection solution for secure testing. The experimental results show that the best security is provided by the randomized addition of masked scan flipflop through the scan chain and also provides minimal design difficulty and power expansion overhead with some negligible delay measures. Thus, the proposed technique outperforms the state-of-the-art LUT-based S-box and the composite sub-byte transformation model regarding throughput rate 2 times and 15 times respectively. And security measured in the avalanche effect for the sub-pipelined model has been increased up to 95 per cent with reduced computational complexity. Also, the proposed sub-pipelined S-box utilizing a composite field arithmetic scheme achieves 7 per cent area effectiveness and 2.5 times the hardware complexity compared to the LUT-based model

Power Side Channels in Security ICs: Hardware Countermeasures

Power side-channel attacks are a very effective cryptanalysis technique that can infer secret keys of security ICs by monitoring the power consumption. Since the emergence of practical attacks in the late 90s, they have been a major threat to many cryptographic-equipped devices including smart cards, encrypted FPGA designs, and mobile phones. Designers and manufacturers of cryptographic devices have in response developed various countermeasures for protection. Attacking methods have also evolved to counteract resistant implementations. This paper reviews foundational power analysis attack techniques and examines a variety of hardware design mitigations. The aim is to highlight exposed vulnerabilities in hardware-based countermeasures for future more secure implementations

A constructive and unifying framework for zero-bit watermarking

In the watermark detection scenario, also known as zero-bit watermarking, a watermark, carrying no hidden message, is inserted in content. The watermark detector checks for the presence of this particular weak signal in content. The article looks at this problem from a classical detection theory point of view, but with side information enabled at the embedding side. This means that the watermark signal is a function of the host content. Our study is twofold. The first step is to design the best embedding function for a given detection function, and the best detection function for a given embedding function. This yields two conditions, which are mixed into one `fundamental' partial differential equation. It appears that many famous watermarking schemes are indeed solution to this `fundamental' equation. This study thus gives birth to a constructive framework unifying solutions, so far perceived as very different.Comment: submitted to IEEE Trans. on Information Forensics and Securit