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

MOIM: a novel design of cryptographic hash function

A hash function usually has two main components: a compression function or permutation function and mode of operation. In this paper, we propose a new concrete novel design of a permutation based hash functions called MOIM. MOIM is based on concatenating two parallel fast wide pipe constructions as a mode of operation designed by Nandi and Paul, and presented at Indocrypt 2010 where the size of the internal state is significantly larger than the size of the output. And the permutations functions used in MOIM are inspired from the SHA-3 finalist Grøstl hash function which is originally inspired from Rijndael design (AES). As a consequence there is a very strong confusion and diffusion in MOIM. Also, we show that MOIM resists all the generic attacks and Joux attack in two defense security levels

On the Security of HB# against a Man-in-the-Middle Attack

At EuroCrypt ’08, Gilbert, Robshaw and Seurin proposed HB# to improve on HB+ in terms of transmission cost and security against man-in-the-middle attacks. Although the security of HB# is formally proven against a certain class of man- in-the-middle adversaries, it is only conjectured for the general case. In this paper, we present a general man-in-the-middle attack against HB# and Random-HB#, which can also be applied to all anterior HB-like protocols, that recovers the shared secret in 225 or 220 authentication rounds for HB# and 234 or 228 for Random-HB#, depending on the parameter set. We further show that the asymptotic complexity of our attack is polynomial under some conditions on the parameter set which are met on one of those proposed in [8]

The Design Space of Lightweight Cryptography

International audienceFor constrained devices, standard cryptographic algorithms can be too big, too slow or too energy-consuming. The area of lightweight cryptography studies new algorithms to overcome these problems. In this paper, we will focus on symmetric-key encryption, authentication and hashing. Instead of providing a full overview of this area of research, we will highlight three interesting topics. Firstly, we will explore the generic security of lightweight constructions. In particular, we will discuss considerations for key, block and tag sizes, and explore the topic of instantiating a pseudorandom permutation (PRP) with a non-ideal block cipher construction. This is inspired by the increasing prevalence of lightweight designs that are not secure against related-key attacks, such as PRINCE, PRIDE or Chaskey. Secondly, we explore the efficiency of cryptographic primitives. In particular, we investigate the impact on efficiency when the input size of a primitive doubles. Lastly, we provide some considerations for cryptographic design. We observe that applications do not always use cryptographic algorithms as they were intended, which negatively impacts the security and/or efficiency of the resulting implementations

Smart homes under siege: Assessing the robustness of physical security against wireless network attacks

© 2024 The Authors. Published by Elsevier Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Nowadays domestic smart security devices, such as smart locks, smart doorbells, and security cameras, are becoming increasingly popular with users, due to their ease of use, convenience, and declining prices. Unlike conventional non-smart security devices, such as alarms and locks, performance standards for smart security devices, such as the British TS 621, are not easily understandable by end users due to the technical language employed. Users also have very few sources of unbiased information regarding product performance in real world conditions and protection against attacks from cyber attacker-burglars and, as a result, tend to take manufacturer claims at face value. This means that, as this work proves, users may be exposed to threats, such as theft, impersonation (should an attacker steal their credentials), and even physical injury, if the device fails and is used to prevent access to hazardous environments. As such, this paper deploys several attacks using popular wireless attack vectors (i.e., 433MHz radio, Bluetooth, and RFID) against domestic smart security devices to assess the protection offered against a cyber attacker-burglar. Our results suggest that users are open to considerable cyber physical attacks, irrespective if they use lesser known (i.e., no name) or branded smart security devices, due to the poor security offered by these devices.Peer reviewe

Functional Encryption as Mediated Obfuscation

We introduce a new model for program obfuscation, called mediated obfuscation. A mediated obfuscation is a 3-party protocol for evaluating an obfuscated program that requires minimal interaction and limited trust. The party who originally supplies the obfuscated program need not be online when the client wants to evaluate the program. A semi-trusted third-party mediator allows the client to evaluate the program, while learning nothing about the obfuscated program or the client’s inputs and outputs. Mediated obfuscation would provide the ability for a software vendor to safely outsource the less savory aspects (like accounting of usage statistics, and remaining online to facilitate access) of “renting out” access to proprietary software. We give security definitions for this new obfuscation paradigm, and then present a simple and generic construction based on functional encryption. If a functional encryption scheme supports decryption functionality F (m, k), then our construction yields a mediated obfuscation of the class of functions {F (m, ·) | m}. In our construction, the interaction between the client and the mediator is minimal (much more efficient than a general- purpose multi-party computation protocol). Instantiating with existing FE constructions, we achieve obfuscation for point-functions with output (under a strong “virtual black-box” notion of security), and a general feasibility result for obfuscating conjunctive normal form and disjunctive normal form formulae (under a weaker “semantic” notion of security). Finally, we use mediated obfuscation to illustrate a connection between worst-case and average-case static obfuscation. In short, an average-case (static) obfuscation of some component of a suitable functional encryption scheme yields a worst-case (static) obfuscation for a related class of functions. We use this connection to demonstrate new impossibility results for average-case (static) obfuscation