Differential Cryptanalysis of Round-Reduced Sparx-64/128

Sparx is a family of ARX-based block ciphers designed according to the long-trail strategy (LTS) that were both introduced by Dinu et al. at ASIACRYPT'16. Similar to the wide-trail strategy, the LTS allows provable upper bounds on the length of differential characteristics and linear paths. Thus, the cipher is a highly interesting target for third-party cryptanalysis. However, the only third-party cryptanalysis on Sparx-64/128 to date was given by Abdelkhalek et al. at AFRICACRYPT'17 who proposed impossible-differential attacks on 15 and 16 (out of 24) rounds. In this paper, we present chosen-ciphertext differential attacks on 16 rounds of Sparx-64/128. First, we show a truncated-differential analysis that requires 232232 chosen ciphertexts and approximately 293293 encryptions. Second, we illustrate the effectiveness of boomerangs on Sparx by a rectangle attack that requires approximately 259.6259.6 chosen ciphertexts and about 2122.22122.2 encryption equivalents. Finally, we also considered a yoyo attack on 16 rounds that, however, requires the full codebook and approximately 21262126 encryption equivalents

MergeMAC:A MAC for Authentication with Strict Time Constraints and Limited Bandwidth

This paper presents MergeMAC, a MAC that is particularly suitable for environments with strict time requirements and extremely limited bandwidth. MergeMAC computes the MAC by splitting the message into two parts. We use a pseudorandom function (PRF) to map messages to random bit strings and then merge them with a very efficient keyless function. The advantage of this approach is that the outputs of the PRF can be cached for frequently needed message parts. We demonstrate the merits of MergeMAC for authenticating messages on the CAN bus where bandwidth is extremely limited and caching can be used to recover parts of the message counter instead of transmitting it. We recommend an instantiation of the merging function MERGE and analyze the security of our construction. Requirements for a merging function are formally defined and the resulting EUF-CMA security of MergeMAC is proven

Requirements and Recommendations for IoT/IIoT Models to automate Security Assurance through Threat Modelling, Security Analysis and Penetration Testing

The factories of the future require efficient interconnection of their physical machines into the cyber space to cope with the emerging need of an increased uptime of machines, higher performance rates, an improved level of productivity and a collective collaboration along the supply chain. With the rapid growth of the Internet of Things (IoT), and its application in industrial areas, the so called Industrial Internet of Things (IIoT)/Industry 4.0 emerged. However, further to the rapid growth of IoT/IIoT systems, cyber attacks are an emerging threat and simple manual security testing can often not cope with the scale of large IoT/IIoT networks. In this paper, we suggest to extract metadata from commonly used diagrams and models in a typical software development process, to automate the process of threat modelling, security analysis and penetration testing, without detailed prior security knowledge. In that context, we present requirements and recommendations for metadata in IoT/IIoT models that are needed as necessary input parameters of security assurance tools.Comment: 8 pages, Proceedings of the 14th International Conference on Availability, Reliability and Security (ARES 2019) (ARES '19), August 26-29, 2019, Canterbury, United Kingdo

SoK: Cyber-Attack Taxonomy of Distributed Ledger- and Legacy Systems-based Financial Infrastructures

Nowadays, virtually all products and services offered by financial institutions are backed by technology. While the frontend banking services seem to be simple, the core-banking backend systems and architecture are complex and often based on legacy technologies. Customer-facing applications and services are evolving rapidly, yet they have data dependencies on core banking systems running on ancient technology standards. While those legacy systems are preferred for their stability, reliability, availability, and security properties, in adapting the frontends and services many security and privacy issues can occur. Clearly, this issues are arising as those systems have been designed decades ago, without considering the enormous amounts of data that they are required to handle and also considering different threat scenarios. Moreover, the trend towards using new technologies such as Distributed Ledger Technologies (DLT) has also emerged in the financial sector. As the nodes in DLT systems are decentralized, additional security threats come to light. The focus of this work is the security of financial technologies in the FinTech domain. We provide relevant categorization and taxonomies for a better understanding of the main cyber-attack types, and suitable countermeasures. Our findings are supported by using security-by-design principles for some selected critical financial use-cases, and include a detailed discussion of the resulting threats, attack vectors and security recommendations

Related-Key Impossible-Differential Attack on Reduced-Round Skinny

At CRYPTO’16, Beierle et al. presented SKINNY, a family of lightweight tweakable block ciphers intended to compete with the NSA designs SIMON and SPECK. SKINNY can be implemented efficiently in both soft- and hardware and supports block sizes of 64 and 128 bits as well as tweakey sizes of 64, 128, 192 and 128, 256, 384 bits respectively. This paper presents a related-tweakey impossible-differential attack on up to 23 (out of 36) rounds of SKINNY-64/128 for different tweak sizes. All our attacks can be trivially extended to SKINNY-128/128

Zero-Correlation Attacks on Tweakable Block Ciphers with Linear Tweakey Expansion

The design and analysis of dedicated tweakable block ciphers is a quite recent and very active research field that provides an ongoing stream of new insights. For instance, results of Kranz, Leander, and Wiemer from FSE 2017 show that the addition of a tweak using a linear tweak schedule does not introduce new linear characteristics. In this paper, we consider – to the best of our knowledge – for the first time the effect of the tweak on zero-correlation linear cryptanalysis for ciphers that have a linear tweak schedule. It turns out that the tweak can often be used to get zero-correlation linear hulls covering more rounds compared to just searching zero-correlation linear hulls on the data-path of a cipher. Moreover, this also implies the existence of integral distinguishers on the same number of rounds. We have applied our technique on round reduced versions of Qarma, Mantis, and Skinny. As a result, we can present – to the best of our knowledge – the best attack (with respect to number of rounds) on a round-reduced variant of Qarma

Mind the Gap - A Closer Look at the Security of Block Ciphers against Differential Cryptanalysis

Resistance against differential cryptanalysis is an important design criteria for any modern block cipher and most designs rely on finding some upper bound on probability of single differential characteristics. However, already at EUROCRYPT'91, Lai et al. comprehended that differential cryptanalysis rather uses differentials instead of single characteristics. In this paper, we consider exactly the gap between these two approaches and investigate this gap in the context of recent lightweight cryptographic primitives. This shows that for many recent designs like Midori, Skinny or Sparx one has to be careful as bounds from counting the number of active S-boxes only give an inaccurate evaluation of the best differential distinguishers. For several designs we found new differential distinguishers and show how this gap evolves. We found an 8-round differential distinguisher for Skinny-64 with a probability of 2−56.932−56.93, while the best single characteristic only suggests a probability of 2−722−72. Our approach is integrated into publicly available tools and can easily be used when developing new cryptographic primitives. Moreover, as differential cryptanalysis is critically dependent on the distribution over the keys for the probability of differentials, we provide experiments for some of these new differentials found, in order to confirm that our estimates for the probability are correct. While for Skinny-64 the distribution over the keys follows a Poisson distribution, as one would expect, we noticed that Speck-64 follows a bimodal distribution, and the distribution of Midori-64 suggests a large class of weak keys

Software Benchmarking of the 2nd^{\text{nd}} round CAESAR Candidates

The software performance of cryptographic schemes is an important factor in the decision to include such a scheme in real-world protocols like TLS, SSH or IPsec. In this paper, we develop a benchmarking framework to perform software performance measurements on authenticated encryption schemes. In particular, we apply our framework to independently benchmark the 29 remaining 2$^\text{nd}$ round candidates of the CAESAR competition. Many of these candidates have multiple parameter choices, or deploy software optimised versions raising our total number of benchmarked implementations to 232. We illustrate our results in various diagrams and hope that our contribution helps developers to find an appropriate cipher in their selection choice

Zero-Correlation Attacks on Tweakable Block Ciphers with Linear Tweakey Expansion

The design and analysis of dedicated tweakable block ciphers is a quite recent and very active research field that provides an ongoing stream of new insights. For instance, results of Kranz, Leander, and Wiemer from FSE 2017 show that the addition of a tweak using a linear tweak schedule does not introduce new linear characteristics. In this paper, we consider – to the best of our knowledge – for the first time the effect of the tweak on zero-correlation linear cryptanalysis for ciphers that have a linear tweak schedule. It turns out that the tweak can often be used to get zero-correlation linear hulls covering more rounds compared to just searching zero-correlation linear hulls on the data-path of a cipher. Moreover, this also implies the existence of integral distinguishers on the same number of rounds. We have applied our technique on round reduced versions of Qarma, Mantis, and Skinny. As a result, we can present – to the best of our knowledge – the best attack (with respect to number of rounds) on a round-reduced variant of Qarma