New Second Preimage Attacks on Dithered Hash Functions with Low Memory Complexity

Dithered hash functions were proposed by Rivest as a method to mitigate second preimage attacks on Merkle-Damgard hash functions. Despite that, second preimage attacks against dithered hash functions were proposed by Andreeva et al. One issue with these second preimage attacks is their huge memory requirement in the precomputation and the online phases. In this paper, we present new second preimage attacks on the dithered Merkle-Damgard construction. These attacks consume significantly less memory in the online phase (with a negligible increase in the online time complexity) than previous attacks. For example, in the case of MD5 with the Keranen sequence, we reduce the memory complexity from about 2^51 blocks to about 2^26.7 blocks (about 545 MB). We also present an essentially memoryless variant of Andreeva et al. attack. In case of MD5-Keranen or SHA1-Keranen, the offline and online memory complexity is 2^15.2 message blocks (about 188–235 KB), at the expense of increasing the offline time complexity

Evaluating the Security of Merkle-Damgård Hash Functions and Combiners in Quantum Settings

In this work, we evaluate the security of Merkle-Damgård (MD) hash functions and their combiners (XOR and concatenation combiners) in quantum settings. Two main quantum scenarios are considered, including the scenario where a substantial amount of cheap quantum random access memory (qRAM) is available and where qRAM is limited and expensive to access. We present generic quantum attacks on the MD hash functions and hash combiners, and carefully analyze the complexities under both quantum scenarios. The considered securities are fundamental requirements for hash functions, including the resistance against collision and (second-)preimage. The results are consistent with the conclusions in the classical setting, that is, the considered resistances of the MD hash functions and their combiners are far less than ideal, despite the significant differences in the expected security bounds between the classical and quantum settings. Particularly, the generic attacks can be improved significantly using quantum computers under both scenarios. These results serve as an indication that classical hash constructions require careful security re-evaluation before being deployed to the post-quantum cryptography schemes

Quantum cryptography: key distribution and beyond

Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK

Impacts and Risk of Generative AI Technology on Cyber Defense

Generative Artificial Intelligence (GenAI) has emerged as a powerful technology capable of autonomously producing highly realistic content in various domains, such as text, images, audio, and videos. With its potential for positive applications in creative arts, content generation, virtual assistants, and data synthesis, GenAI has garnered significant attention and adoption. However, the increasing adoption of GenAI raises concerns about its potential misuse for crafting convincing phishing emails, generating disinformation through deepfake videos, and spreading misinformation via authentic-looking social media posts, posing a new set of challenges and risks in the realm of cybersecurity. To combat the threats posed by GenAI, we propose leveraging the Cyber Kill Chain (CKC) to understand the lifecycle of cyberattacks, as a foundational model for cyber defense. This paper aims to provide a comprehensive analysis of the risk areas introduced by the offensive use of GenAI techniques in each phase of the CKC framework. We also analyze the strategies employed by threat actors and examine their utilization throughout different phases of the CKC, highlighting the implications for cyber defense. Additionally, we propose GenAI-enabled defense strategies that are both attack-aware and adaptive. These strategies encompass various techniques such as detection, deception, and adversarial training, among others, aiming to effectively mitigate the risks posed by GenAI-induced cyber threats

Cyber Safety: A theoretical Insight

This paper is written by the EUCPN Secretariat following the topic of the Estonian Presidency of the Network, which is Cyber Safety. It gives a theoretical insight in what Cyber Safety is. Furthermore, we take interest in what the exact object is of cybercrime and have a deeper look into two European policy priorities, namely cyber-attacks and payment fraud. Moreover, these priorities are the subject of the European Crime Prevention award. The goal of this paper is to add to the digital awareness of local policy-makers and practitioners on a theoretical level. A toolbox will follow with legislative measures, existing policies and best practices on this topic

Foiling covert channels and malicious classical post-processing units in quantum key distribution

The existing paradigm for the security of quantum key distribution (QKD) suffers from two fundamental weaknesses. First, covert channels have emerged as an important threat and have attracted a lot of attention in security research in conventional information and communication systems. Covert channels (e.g. memory attacks) can fatally break the security of even deviceindependent quantum key distribution (DI-QKD), whenever QKD devices are re-used. Second, it is often implicitly assumed that the classical post-processing units of a QKD system are trusted. This is a rather strong assumption and is very hard to justify in practice. Here, we propose a new paradigm for the security of QKD that addresses these two fundamental problems. Specifically, we show that by using verifiable secret sharing and multiple optical devices and classical post-processing units, one could re-establish the security of QKD. Our techniques are rather general and they apply to both DI-QKD and non-DI-QKD.Ministerio de Economía y Competitividad | Ref. TEC2014-54898-RMinisterio de Economía y Competitividad | Ref. TEC2017-88243-

Some Cryptanalytic Results on Zipper Hash and Concatenated Hash

At SAC 2006, Liskov proposed the zipper hash, a technique for constructing secure (indifferentiable from random oracles) hash functions based on weak (invertible) compression functions. Zipper hash is a two pass scheme, which makes it unfit for practical consideration. But, from the theoretical point of view it seemed to be secure, as it had resisted standard attacks for long. Recently, Andreeva {\em et al.} gave a forced-suffix herding attack on the zipper hash, and Chen and Jin showed a second preimage attack provided $f_1$ is strong invertible. In this paper, we analyse the construction under the random oracle model as well as when the underlying compression functions have some weakness. We show (second) preimage, and herding attacks on an $n$-bit zipper hash and its relaxed variant with $f_1 = f_2$, all of which require less than $2^{n}$ online computations. Hoch and Shamir have shown that the concatenated hash offers only $\frac{n}{2}$-bits security when both the underlying compression functions are strong invertible. We show that the bound is tight even when only one of the underlying compression functions is strong invertible

The Usage of Counter Revisited: Second-Preimage Attack on New Russian Standardized Hash Function

International audienceStreebog is a new Russian hash function standard. It follows the HAIFA framework as domain extension algorithm and claims to resist recent generic second-preimage attacks with long messages. However, we demonstrate in this article that the specific instantiation of the HAIFA framework used in Streebog makes it weak against such attacks. More precisely, we observe that Streebog makes a rather poor usage of the HAIFA counter input in the compression function, which allows to con-struct second-preimages on the full Streebog-512 with a complexity as low as n × 2 n/2 (namely 2 266) compression function evaluations for long messages. This complexity has to be compared with the expected 2 512 computations bound that an ideal hash function should provide. Our work is a good example that one must be careful when using a design framework for which not all instances are secure. HAIFA helps designers to build a secure hash function, but one should pay attention to the way the counter is handled inside the compression function

The Statistics and Security of Quantum Key Distribution

In this work our aim has been to elucidate our theoretical developments that bolster the efficiency of quantum key distribution systems leading to more secure communication channels, as well as develop rigorous methods for their analysis. After a review of the necessary mathematical and physical preliminaries and a discussion of the present state of quantum communication technologies, we begin by investigating the Trojan Horse Attack, a form of side-channel attack that could threaten the security of existing key distribution protocols. We examine the secret key rates that may be achieved when an eavesdropper may use any Gaussian state in the presence of thermal noise, and prove that the coherent state is optimal in this case. We then allow the eavesdropper to use any separable state, and show that this gives a key rate bound close to that of the coherent state. We develop a protocol for a quantum repeater that makes use of the double-heralding procedure for entanglement-generation. In our analysis, we include statistical effects on the key rate arising from probabilistic entanglement generation, which results in some quantum memories decohering while other sections complete their entanglement generation attempts. We show that this results in secure communication being possible over thousands of kilometres, allowing for intercontinental key distribution. Finally, we investigate in more depth the statistical issues that arise in general quantum repeater networks. We develop a framework based on Markov chains and probability generating functions, to show how one may easily calculate an analytic expression for the completion time of a probabilistic process. We then extend this method to show how one may track the distribution of the number of errors that accrue in operating such a process. We apply these methods to a typical quantum repeater network to get new tight bounds on the achievable key rates