This paper deals with reducing the secret key computation time of small scale variants of the AES cipher using algebraic cryptanalysis, which is accelerated by data mining methods. This work is based on the known plaintext attack and aims to speed up the calculation of the secret key by processing the polynomial equations extracted from plaintext-ciphertext pairs. Specifically, we propose to transform the overdefined system of polynomial equations over GF(2) into a new system so that the...

A Key Derivation Function (KDF) generates a uniform and highly random key-stream from weakly random key material. KDFs are broadly used in various security protocols such as digital signatures and key exchange protocols. HKDF, the most deployed KDF in practice, is based on the extract-then-expand paradigm. It is presently used, among others, in the Signal Protocol for end-to-end encrypted messaging. HKDF is a generic KDF for general input sources and thus is not optimized for...

The threat of physical side-channel attacks and their countermeasures is a widely researched field. Most physical side-channel attacks rely on the unavoidable influence of computation or storage on voltage or current fluctuations. Such data-dependent influence can be exploited by, for instance, power or electromagnetic analysis. In this work, we introduce a novel non-invasive physical side-channel attack, which exploits the data-dependent changes in the impedance of the chip. Our attack...

In SAC’14, Biham and Carmeli presented a novel attack on DES, involving a variation of Partitioning Cryptanalysis. This was further extended in ToSC’18 by Biham and Perle into the Conditional Linear Cryptanalysis in the context of Feistel ciphers. In this work, we formalize this cryptanalytic technique for block ciphers in general and derive several properties. This conditional approximation is then used to approximate the inv : GF(2^8) → GF(2^8) : x → x^254 function which forms the...

Because of the rapid growth of Internet of Things (IoT), embedded systems have become an interesting target for experienced attackers. ESP32~\cite{tech-ref-man} is a low-cost and low-power system on chip (SoC) series created by Espressif Systems. The firmware extraction of such embedded systems is a real threat to the manufacturer as it breaks its intellectual property and raises the risk of creating equivalent systems with less effort and resources. In 2019,...

Deep neural networks (DNN) have become a significant threat to the security of cryptographic implementations with regards to side-channel analysis (SCA), as they automatically combine the leakages without any preprocessing needed, leading to a more efficient attack. However, these DNNs for SCA remain mostly black-box algorithms that are very difficult to interpret. Benamira \textit{et al.} recently proposed an interpretable neural network called Truth Table Deep Convolutional Neural Network...

We investigate the susceptibility of the Texas Instruments SimpleLink platform microcontrollers to non-invasive physical attacks. We extracted the ROM bootloader of these microcontrollers and then analysed it using static analysis augmented with information obtained through emulation. We demonstrate a voltage fault injection attack targeting the ROM bootloader that allows to enable debug access on a previously locked microcontroller within seconds. Information provided by Texas Instruments...

ARM-based Android smartphones rely on the TrustZone hardware support for a Trusted Execution Environment (TEE) to implement security-sensitive functions. The TEE runs a separate, isolated, TrustZone Operating System (TZOS), in parallel to Android. The implementation of the cryptographic functions within the TZOS is left to the device vendors, who create proprietary undocumented designs. In this work, we expose the cryptographic design and implementation of Android's Hardware-Backed...

Block ciphers such as the Advanced Encryption Standard (Rijndael) are used extensively in practice, yet our understanding of their security continues to be highly incomplete. This paper promotes and continues a research program aimed at *proving* the security of block ciphers against important and well-studied classes of attacks. In particular, we initiate the study of (almost) $t$-wise independence of concrete block-cipher construction paradigms such as substitution-permutation networks and...

Side-channel attacks exploit information that is leaked from hardware. The differential power analysis (DPA) attack aims at extracting sensitive information that is processed by the operations in a cryptographic primitive. Power traces are collected and subsequently processed using statistical methods. The ChipWhisperer Nano is a low-cost, open-source device that can be used to implement and study side-channel attacks. This paper describes how the DPA attack with the difference of means...

Persistent fault analysis (PFA) consists in guessing block cipher secret keys by biasing their substitution box. This paper improves the original attack of Zhang et al. on AES-128 presented at CHES 2018. By a thorough analysis, the exact probability distribution of the ciphertext (under a uniformly distributed plaintext) is derived, and the maximum likelihood key recovery estimator is computed exactly. Its expression is turned into an attack algorithm, which is shown to be twice more...

The MixColumns operation is an important component providing diffusion for the AES. The branch number of it ensures that any continuous four rounds of the AES have at least 25 active S-Boxes, which makes the AES secure against the differential and linear cryptanalysis. However, the choices of the coefficients of the MixColumns matrix may undermine the AES security against some novel-type attacks. A particular property of the AES MixColumns matrix coefficient has been noticed in recent papers...

Mathematically-secure cryptographic algorithms leak significant side-channel information through their power supplies when implemented on a physical platform. These side-channel leakages can be exploited by an attacker to extract the secret key of an embedded device. The existing state-of-the-art countermeasures mainly focus on the power balancing, gate-level masking, or signal-to-noise (SNR) reduction using noise injection and signature attenuation, all of which suffer either from the...

This paper has four main goals. First, we show how we solved the CHES 2018 AES challenge in the contest using essentially a linear classifier combined with a SAT solver and a custom error correction method. This part of the paper has previously appeared in a preprint by the current authors (e-print report 2019/094) and later as a contribution to a preprint write-up of the solutions by the three winning teams (e-print report 2019/860). Second, we develop a novel deep neural network...

Dynamic and partial reconfiguration together with hardware parallelism make FPGAs attractive as virtualized accelerators. However, recently it has been shown that multi-tenant FPGAs are vulnerable to remote side-channel attacks (SCA) from malicious users, allowing them to extract secret keys without a logical connection to the victim core. Typical mitigations against such attacks are hiding and masking schemes, to increase attackers’ efforts in terms of side-channel measurements. However,...

We take advantage of a recently published open source implementation of the AES protected with a mix of countermeasures against side-channel attacks to discuss both the challenges in protecting COTS devices against such attacks and the limitations of closed source security evaluations. The target implementation has been proposed by the French ANSSI (Agence Nationale de la Sécurité des Systèmes d'Information) to stimulate research on the design and evaluation of side-channel secure...

Deep Neural Networks (DNNs) have recently received significant attention in the side-channel community due to their state-of-the-art performance in security testing of embedded systems. However, research on the subject mostly focused on techniques to improve the attack efficiency in terms of the number of traces required to extract secret parameters. What has not been investigated in detail is a constructive approach of DNNs as a tool to evaluate and improve the effectiveness of...

Parallel cryptographic implementations are generally considered to be more advantageous than their non-parallel counterparts in mitigating side-channel attacks because of their higher noise-level. So far as we know, the side-channel security of GPU-based cryptographic implementations have been studied in recent years, and those implementations then turn out to be susceptible to some side-channel attacks. Unfortunately, the target parallel implementations in their work do not achieve strict...

Thermal laser stimulation (TLS) is a failure analysis technique, which can be deployed by an adversary to localize and read out stored secrets in the SRAM of a chip. To this date, a few proof-of-concept experiments based on TLS or similar approaches have been reported in the literature, which do not reflect a real attack scenario. Therefore, it is still questionable whether this attack technique is applicable to modern ICs equipped with side-channel countermeasures. The primary aim of this...

The ARM TrustZone is a security extension which is used in recent Samsung flagship smartphones to create a Trusted Execution Environment (TEE) called a Secure World, which runs secure processes (Trustlets). The Samsung TEE includes cryptographic key storage and functions inside the Keymaster trustlet. The secret key used by the Keymaster trustlet is derived by a hardware device and is inaccessible to the Android OS. However, the ARM32 AES implementation used by the Keymaster is vulnerable to...

Malicious exploitation of faults for extracting secrets is one of the most practical and potent threats to modern cryptographic primitives. Interestingly, not every possible fault for a cryptosystem is maliciously exploitable, and evaluation of the exploitability of a fault is nontrivial. In order to devise precise defense mechanisms against such rogue faults, a comprehensive knowledge is required about the exploitable part of the fault space of a cryptosystem. Unfortunately, the fault space...

Independent Component Analysis (ICA) is a powerful technique for blind source separation. It has been successfully applied to signal processing problems, such as feature extraction and noise reduction, in many different areas including medical signal processing and telecommunication. In this work, we propose a framework to apply ICA to denoise side-channel measurements and hence to reduce the complexity of key recovery attacks. Based on several case studies, we afterwards demonstrate the...

White-box cryptography protects key extraction from software implementations of cryptographic primitives. It is widely deployed in DRM and mobile payment applications in which a malicious attacker might control the entire execution environment. So far, no provably secure white-box implementation of AES has been put forward, and all the published practical constructions are vulnerable to differential computation analysis (DCA) and differential fault analysis (DFA). As a consequence, the...

Whitebox cryptography aims to ensure the security of cryptographic algorithms in the whitebox model where the adversary has full access to the execution environment. To attain security in this setting is a challenging problem: Indeed, all published whitebox implementations of standard symmetric-key algorithms such as AES to date have been practically broken. However, as far as we know, no whitebox implementation in real-world products has suffered from a key recovery attack. This is due to...

Within the next few years, billions of IoT devices will densely populate our cities. In this paper we describe a new type of threat in which adjacent IoT devices will infect each other with a worm that will spread explosively over large areas in a kind of nuclear chain reaction, provided that the density of compatible IoT devices exceeds a certain critical mass. In particular, we developed and verified such an infection using the popular Philips Hue smart lamps as a platform. The worm...

Classical fault attacks such as Differential Fault Analysis~(DFA) as well as biased fault attacks such as the Differential Fault Intensity Analysis~(DFIA) have been a major threat to cryptosystems in recent times. DFA uses pairs of fault-free and faulty ciphertexts to recover the secret key. DFIA, on the other hand, combines principles of side channel analysis and fault attacks to try and extract the key using faulty ciphertexts only. Till date, no effective countermeasure that can thwart...

In this paper we detail techniques that can be used to analyze and attack an AES implementation on an FPGA from the primary (i.e., external) side of a switched-mode power supply. Our attack only requires measurements of the duty cycle of the power supply, and then increases the signal-to-noise ratio (SNR) though averaging, deconvolution and wavelet based detrending. The result is an exploitable source of leakage that allows a secret key to be determined from low-frequency power...

The Side Channel Cube Attack (SCCA) is a kind of Algebraic Side Channel Attack (ASCA) consisting of theoretical and practical aspects. This paper presents a general framework for the SCCA (called an Iterative SCCA (ISCCA)) on block ciphers in which these aspects are explained and the requirements are listed. On the theoretical side, we use extracting quadratic equations, recognizing iterated chosen plaintexts, and cube iteration to improve the SCCA on block ciphers. On the experimental side,...

White-box cryptography aims to protect the secret key of a cipher in an environment in which an adversary has full access to the implementation of the cipher and its execution environment. In 2002, Chow, Eisen, Johnson and van Oorschot proposed a white-box implementation of AES. In 2004, Billet, Gilbert and Ech-Chatbi presented an efficient attack (referred to as the BGE attack) on this implementation, extracting its embedded AES key with a work factor of $2^{30}$. In 2012, Tolhuizen...

White-box cryptography concerns the design and analysis of implementations of cryptographic algorithms engineered to execute on untrusted platforms. Such implementations are said to operate in a \emph{white-box attack context}. This is an attack model where all details of the implementation are completely visible to an attacker: not only do they see input and output, they see every intermediate computation that happens along the way. The goal of a white-box attacker when targeting...

This paper is a short summary of a real world AES key extraction performed on a military grade FPGA marketed as 'virtually unbreakable' and 'highly secure'. We demonstrated that it is possible to extract the AES key from the Actel/Microsemi ProASIC3 chip in a time of 0.01 seconds using a new side-channel analysis technique called Pipeline Emission Analysis (PEA). This new technique does not introduce a new form of side-channel attacks (SCA), it introduces a substantially improved method of...

\texttt{LEX} is a stream cipher proposed by Alex Biryukov. It was selected to phase $3$ of the eSTREAM competition. \texttt{LEX} is based on the Advanced Encryption Standard {\texttt{AES}) block cipher and uses a methodology called {\em Leak Extraction}, proposed by Biryukov himself. However Dunkelman and Keller show that a key recovery attack exists against \texttt{LEX}. Their attack requires $2^{36.3}$ bytes of keystream produced by the same key and works with a time complexity...

This paper is a short summary of our real-world side-channel analysis of the bitstream encryption mechanism provided by Xilinx FPGAs. This work covers our results analyzing the Virtex 4, Virtex 5, and Spartan 6 family showing that the encryption mechanism can be completely broken with moderate effort. The presented results provide an overview of a practical real-world analysis and should help practitioners to judge the necessity to implement side-channel countermeasures. We demonstrate...

The famous Leftover Hash Lemma (LHL) states that (almost) universal hash functions are good randomness extractors. Despite its numerous applications, LHL-based extractors suffer from the following two drawbacks: (1) Large Entropy Loss: to extract v bits from distribution X of min-entropy m which are e-close to uniform, one must set v <= m - 2*log(1/e), meaning that the entropy loss L = m-v >= 2*log(1/e). (2) Large Seed Length: the seed length n of (almost) universal hash function required...

A method for extracting cryptographic key material from DRAM used in modern computers has been recently proposed in [9]; the technique was called Cold Boot attacks. When considering block ciphers, such as the AES and DES, simple algorithms were also proposed in [9] to recover the cryptographic key from the observed set of round subkeys in memory (computed via the cipher’s key schedule operation), which were however subject to errors due to memory bits decay. In this work we extend this...

The fundamental problem of extracting the highest possible amount of key-related information using the lowest possible number of measurements is central to side-channel attacks against embedded implementations of cryptographic algorithms. To address it, this work proposes a novel framework enhancing side-channel collision attacks with divide-and-conquer attacks such as differential power analysis (DPA). An information-theoretical metric is introduced for the evaluation of collision detection...

LEX is a stream cipher proposed by Alex Biryukov. It was selected to phase 3 of the eSTREAM competition. LEX is based on the Advanced Encryption Standard (AES) block cipher and uses a methodology called "Leak Extraction", proposed by Biryukov himself. In this paper, we cryptanalyze LEX using two related keys. We have mounted a key recovery attack on LEX, which using $2^{54. 3}$ key streams yields a complete round key with $2^{102}$ operations. This improves the existing best...

The design of embedded processors demands a careful trade-off between many conflicting objectives such as performance, silicon area and power consumption. Finding such a trade-off can often ignore the issue of security, which can cause, otherwise secure, software to leak information through so-called micro-architectural side channels. In this paper we show that early-terminating integer multipliers found in many embedded processors (e.g., ARM7TDMI) represent an instance of this problem. The...

A white-box implementation of a block cipher is a software implementation from which it is difficult for an attacker to extract the cryptographic key. Chow et al. published white-box implementations for AES and DES that both have been cryptanalyzed. However, these white-box implementations are based on ideas that can easily be used to derive white-box implementations for other block ciphers as well. As the cryptanalyses published use typical properties of AES and DES, it remains an open...