Differential Analysis of Round-Reduced AES Faulty Ciphertexts

International audienceThis paper describes new Round Reduction analysis attacks on an Advanced Encryption Standard (AES) implemen- tation by laser fault injection. The previous round reduction attacks require both of spatial and temporal accuracies in order to execute only one, two or nine rounds. We present new attacks by more flexible fault injection conditions. Our experiments are carried out on an 8-bit microcontroller which embeds a software AES with pre-calculated round keys. Faults are injected either into the round counter itself or into the reference of its total round number. The attacks may result to the use of a faulty round key at the last one or two executed rounds. The cryptanalysis of the obtained round-reduced faulty ciphertexts resorts to the differentiation techniques used by Differential Fault Analysis

Extending Differential Fault Analysis to Dynamic S-Box Advanced Encryption Standard Implementations

Advanced Encryption Standard (AES) is a worldwide cryptographic standard for symmetric key cryptography. Many attacks try to exploit inherent weaknesses in the algorithm or use side channels to reduce entropy. At the same time, researchers strive to enhance AES and mitigate these growing threats. This paper researches the extension of existing Differential Fault Analysis (DFA) attacks, a family of side channel attacks, on standard AES to Dynamic S-box AES research implementations. Theoretical analysis reveals an expected average keyspace reduction of 2-88:9323 after one faulty ciphertext using DFA on the State of Rotational S-box AES-128 implementations. Experimental results revealed an average 2-88:8307 keyspace reduction and confirmed full key recovery is possible

Electromagnetic glitch on the AES round counter

International audienceThis article presents a Round Addition Analysis on a software implementation of the Advanced Encryption Standard (AES) algorithm. The round keys are computed on-the-fly during each encryption. A non-invasive transient fault injection is achieved on the AES round counter. The attack is performed by injecting a very short electromagnetic glitch on a 32-bit microcontroller based on the arm Cortex-M3 processor. Using this experimental setup, we are able to disrupt the round counter increment at the end of the penultimate round and execute one additional round. This faulty execution enables us to recover the encryption key with only two pairs of corresponding correct and faulty ciphertexts

Integrated Evaluation Platform for Secured Devices

International audienceIn this paper, we describe the structure of a FPGAsmart card emulator. The aim of such an emulator is to improvethe behaviour of the whole architecture when faults occur. Withinthis card, an embedded Advanced Encryption Standard (AES)protected against DFA is inserted as well as a fault injectionblock. We also present the microprocessor core which controlsthe whole card

Reduction in the Number of Fault Injections for Blind Fault Attack on SPN Block Ciphers

In 2014, a new fault analysis called blind fault attack (BFA) was proposed, in which attackers can only obtain the number of different faulty outputs without knowing the public data. The original BFA requires 480,000 fault injections to recover a 128-bit AES key. This work attempts to reduce the number of fault injections under the same attack assumptions. We analyze BFA from an information theoretical perspective and introduce a new probability-based distinguisher. Three approaches are proposed for different attack scenarios. The best one realized a 66.8% reduction of the number of fault injections on AES

An Information Theoretic Perspective on the Differential Fault Analysis against AES

Differential Fault Analysis against AES has been actively studied these years. Based on similar assumptions of the fault injection, different DFA attacks against AES have been proposed. However, it is difficult to understand how different attack results are obtained for the same fault injection. It is also difficult to understand the relationship between similar assumptions of fault injection and the corresponding attack results. This paper reviews the previous DFA attacks against AES based on the information theory, and gives a general and easy understanding of DFA attacks against AES. We managed to apply the analysis on DFA attacks on AES-192 and AES-256, and we propose the attack procedures to reach the theoretically minimal number of fault injections

Efficient Methods for Exploiting Faults Induced at AES Middle Rounds

Faults occurred during the operations in a hardware device cause many problems such as performance deterioration, unreliable output, etc. If a fault occurs in a cryptographic hardware device, the effect can be even serious because an adversary may exploit it to find the secret information stored in the device. More precisely, the adversary can find the key of a block cipher using differential information between correct and faulty ciphertexts obtained by inducing faults during the computation of ciphertexts. This kind of attack is called \emph{Differential Fault Analysis} (DFA). Among many ciphers \emph{Advanced Encryption Standard} (AES) has been the main target of DFA due to its popularity. AES is widely used in different platforms and systems including Intel and AMD microprocessors. Normally DFA on AES exploits faults induced at the last few rounds. Hence, a general countermeasure is to recompute the last few rounds of AES and compare it with the original output. As redundancy is a costly countermeasure, one should ascertain exactly which rounds need to be protected. In 2006, Phan and Yen introduced a new type of DFA, so called Square-DFA, that works even when faults are induced into some middle rounds. However, it is impractical as it requires several hundreds of faulty ciphertexts as well as a bit fault model. In this article, we propose new attacks that need only dozens of faulty ciphertexts in a byte fault model. Normally it is believed that randomly corrupting a byte is easier than corrupting a specific bit. In addition, we extend the attacks to the AES-192 and AES-256, which is the first result in the literature

Fault Analysis Study of the Block Cipher FOX64

FOX is a family of symmetric block ciphers from MediaCrypt AG that helps to secure digital media, communications, and storage. The high-level structure of FOX is the so-called (extended) Lai-Massey scheme. This paper presents a detailed fault analysis of the block cipher FOX64, the 64-bit version of FOX, based on a differential property of tworound Lai-Massey scheme in a fault model. Previous fault attack on FOX64 shows that each round-key (resp. whole round-keys) could be recovered through 11.45 (resp. 183.20) faults on average. Our proposed fault attack, however, can deduce any round-key (except the first one) through 4.25 faults on average (4 in the best case), and retrieve the whole round-keys through 43.31 faults on average (38 in the best case). This implies that the number of needed faults in the fault attack on FOX64 can be significantly reduced. Furthermore, the technique introduced in this paper can be extended to other series of the block cipher family FOX