Statistical cryptanalysis of block ciphers

Since the development of cryptology in the industrial and academic worlds in the seventies, public knowledge and expertise have grown in a tremendous way, notably because of the increasing, nowadays almost ubiquitous, presence of electronic communication means in our lives. Block ciphers are inevitable building blocks of the security of various electronic systems. Recently, many advances have been published in the field of public-key cryptography, being in the understanding of involved security models or in the mathematical security proofs applied to precise cryptosystems. Unfortunately, this is still not the case in the world of symmetric-key cryptography and the current state of knowledge is far from reaching such a goal. However, block and stream ciphers tend to counterbalance this lack of "provable security" by other advantages, like high data throughput and ease of implementation. In the first part of this thesis, we would like to add a (small) stone to the wall of provable security of block ciphers with the (theoretical and experimental) statistical analysis of the mechanisms behind Matsui's linear cryptanalysis as well as more abstract models of attacks. For this purpose, we consider the underlying problem as a statistical hypothesis testing problem and we make a heavy use of the Neyman-Pearson paradigm. Then, we generalize the concept of linear distinguisher and we discuss the power of such a generalization. Furthermore, we introduce the concept of sequential distinguisher, based on sequential sampling, and of aggregate distinguishers, which allows to build sub-optimal but efficient distinguishers. Finally, we propose new attacks against reduced-round version of the block cipher IDEA. In the second part, we propose the design of a new family of block ciphers named FOX. First, we study the efficiency of optimal diffusive components when implemented on low-cost architectures, and we present several new constructions of MDS matrices; then, we precisely describe FOX and we discuss its security regarding linear and differential cryptanalysis, integral attacks, and algebraic attacks. Finally, various implementation issues are considered

A Salad of Block Ciphers

This book is a survey on the state of the art in block cipher design and analysis. It is work in progress, and it has been for the good part of the last three years -- sadly, for various reasons no significant change has been made during the last twelve months. However, it is also in a self-contained, useable, and relatively polished state, and for this reason I have decided to release this \textit{snapshot} onto the public as a service to the cryptographic community, both in order to obtain feedback, and also as a means to give something back to the community from which I have learned much. At some point I will produce a final version -- whatever being a ``final version\u27\u27 means in the constantly evolving field of block cipher design -- and I will publish it. In the meantime I hope the material contained here will be useful to other people

Revisiting Key-alternating Feistel Ciphers for Shorter Keys and Multi-user Security

Key-Alternating Feistel (KAF) ciphers, a.k.a. Feistel-2 models, refer to Feistel networks with round functions of the form $F_i(k_i\oplus x_i)$, where $k_i$ is the (secret) round-key and $F_i$ is a public random function. This model roughly captures the structures of many famous Feistel ciphers, and the most prominent instance is DES. Existing provable security results on KAF assumed independent round-keys and round functions (ASIACRYPT 2004 & FSE 2014). In this paper, we investigate how to achieve security under simpler and more realistic assumptions: with round-keys derived from a short main-key, and hopefully with identical round functions. For birthday-type security, we consider 4-round KAF, investigate the minimal conditions on the way to derive the four round-keys, and prove that when such adequately derived keys and the same round function are used, the 4-round KAF is secure up to $2^{n/2}$ queries. For beyond-birthday security, we focus on 6-round KAF. We prove that when the adjacent round-keys are independent, and independent round-functions are used, the 6 round KAF is secure up to $2^{2n/3}$ queries. To our knowledge, this is the first beyond-birthday security result for KAF without assuming completely independent round-keys. Our results hold in the multi-user setting as well, constituting the first non-trivial multi-user provable security results on Feistel ciphers. We finally demonstrate applications of our results on designing key-schedules and instantiating keyed sponge constructions

A Flexible Ultralight Hardware Security Module for EPC RFID Tags

Due to the rapid growth of using Internet of Things (IoT) devices in daily life, the need to achieve an acceptable level of security and privacy for these devices is rising. Security risks may include privacy threats like gaining sensitive information from a device, and authentication problems from counterfeit or cloned devices. It is more challenging to add security features to extremely constrained devices, such as passive Electronic Product Code (EPC) Radio Frequency Identification (RFID) tags, compared to devices that have more computational and storage capabilities. EPC RFID tags are simple and low-cost electronic circuits that are commonly used in supply chains, retail stores, and other applications to identify physical objects. Most tags today are simple "license plates" that just identify the object they are attached to and have minimal security. Due to the security risks of new applications, there is an important need to implement secure RFID tags. Examples of the security risks for these applications include unauthorized physical tracking and inventorying of tags. The current commercial RFID tag designs use specialised hardware circuits approach. This approach can achieve the lowest area and power consumption; however, it lacks flexibility. This thesis presents an optimized application-specific instruction set architecture (ISA) for an ultralight Hardware Security Module (HSM). HSMs are computing devices that protect cryptographic keys and operations for a device. The HSM combines all security-related functions for passive RFID tag. The goal of this research is to demonstrate that using an application-specific instruction set processor (ASIP) architecture for ultralight HSMs provides benefits in terms of trade-offs between flexibility, extensibility, and efficiency. Our novel application specific instruction-set architecture allows flexibility on many design levels and achieves acceptable security level for passive EPC RFID tag. Our solution moves a major design effort from hardware to software, which largely reduces the final unit cost. Our ASIP processor can be implemented with 4,662 gate equivalent units (GEs) for 65 nm CMOS technology excluding cryptographic units and memories. We integrated and analysed four cryptographic modules: AES and Simeck block ciphers, WG-5 stream cipher, and ACE authenticated encryption module. Our HSM achieves very good efficiencies for both block and stream ciphers. Specifically for the AES cipher, we improve over a previous programmable AES implementation result by 32x. We increase performance dramatically and increase/decrease area by 17.97/17.14% respectively. These results fulfill the requirements of extremely constrained devices and allow the inclusion of cryptographic units into the datapath of our ASIP processor

Differential Attacks Against SPN: A Thorough Analysis

International audienceThis work aims at determining when the two-round maximum expected differential probability in an SPN with an MDS diffusion layer is achieved by a differential having the fewest possible active Sboxes. This question arises from the fact that minimum-weight differentials include the best differentials for the AES and several variants. However, we exhibit some SPN for which the two-round MEDP is achieved by some differentials involving a number of active Sboxes which exceeds the branch number of the linear layer. On the other hand, we also prove that, for some particular families of Sboxes, the two-round MEDP is always achieved for minimum-weight differentials

Efficient Error detection Architectures for Low-Energy Block Ciphers with the Case Study of Midori Benchmarked on FPGA

Achieving secure, high performance implementations for constrained applications such as implantable and wearable medical devices is a priority in efficient block ciphers. However, security of these algorithms is not guaranteed in presence of malicious and natural faults. Recently, a new lightweight block cipher, Midori, has been proposed which optimizes the energy consumption besides having low latency and hardware complexity. This algorithm is proposed in two energy-efficient varients, i.e., Midori64 and Midori128, with block sizes equal to 64 and 128 bits. In this thesis, fault diagnosis schemes for variants of Midori are proposed. To the best of the our knowledge, there has been no fault diagnosis scheme presented in the literature for Midori to date. The fault diagnosis schemes are provided for the nonlinear S-box layer and for the round structures with both 64-bit and 128-bit Midori symmetric key ciphers. The proposed schemes are benchmarked on field-programmable gate array (FPGA) and their error coverage is assessed with fault-injection simulations. These proposed error detection architectures make the implementations of this new low-energy lightweight block cipher more reliable

Design of Efficient Symmetric-Key Cryptographic Algorithms

兵庫県立大学大学院202

Out of Oddity – New Cryptanalytic Techniques Against Symmetric Primitives Optimized for Integrity Proof Systems

International audienceThe security and performance of many integrity proof systems like SNARKs, STARKs and Bulletproofs highly depend on the underlying hash function. For this reason several new proposals have recently been developed. These primitives obviously require an in-depth security evaluation, especially since their implementation constraints have led to less standard design approaches. This work compares the security levels offered by two recent families of such primitives, namely GMiMC and HadesMiMC. We exhibit low-complexity distinguishers against the GMiMC and HadesMiMC permutations for most parameters proposed in recently launched public challenges for STARK-friendly hash functions. In the more concrete setting of the sponge construction corresponding to the practical use in the ZK-STARK protocol, we present a practical collision attack on a round-reduced version of GMiMC and a preimage attack on some instances of HadesMiMC. To achieve those results, we adapt and generalize several cryptographic techniques to fields of odd characteristic