Efficient oblivious transfer with membership verification

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Digital Forensic Analysis of Telegram Messenger App in Android Virtual Environment

The paper provides an in-depth analysis of the artifacts generated by the Telegram Messenger application on Android OS which provides secure communications between individuals, groups, and channels. Since the past few years, the application went through major changes and updates and the latest version’s artifacts varied from the previous ones. Our methodology is based on the set of experiments designed to generate the artifacts from various use cases on the virtualized environment. The acquired artifacts such as messages, their location, and data structure how they relate to one another were studied and were then compared to the older versions. By correlating the artifacts of newer version with the older ones, it shows how the application have been upgraded behind the scenes and by incorporating those results can provide investigators better understanding and insight for the certain evidence in a potential cybercrime case

A Bit-Vector Differential Model for the Modular Addition by a Constant

ARX algorithms are a class of symmetric-key algorithms constructed by Addition, Rotation, and XOR, which achieve the best software performances in low-end microcontrollers. To evaluate the resistance of an ARX cipher against differential cryptanalysis and its variants, the recent automated methods employ constraint satisfaction solvers, such as SMT solvers, to search for optimal characteristics. The main difficulty to formulate this search as a constraint satisfaction problem is obtaining the differential models of the non-linear operations, that is, the constraints describing the differential probability of each non-linear operation of the cipher. While an efficient bit-vector differential model was obtained for the modular addition with two variable inputs, no differential model for the modular addition by a constant has been proposed so far, preventing ARX ciphers including this operation from being evaluated with automated methods. In this paper, we present the first bit-vector differential model for the n-bit modular addition by a constant input. Our model contains O(log2(n)) basic bit-vector constraints and describes the binary logarithm of the differential probability. We also represent an SMT-based automated method to look for differential characteristics of ARX, including constant additions, and we provide an open-source tool ArxPy to find ARX differential characteristics in a fully automated way. To provide some examples, we have searched for related-key differential characteristics of TEA, XTEA, HIGHT, and LEA, obtaining better results than previous works. Our differential model and our automated tool allow cipher designers to select the best constant inputs for modular additions and cryptanalysts to evaluate the resistance of ARX ciphers against differential attacks.acceptedVersio

Differential Fault Attack on Lightweight Block Cipher PIPO

With the recent development of Internet of Things (IoT) devices, related security issues are also increasing. In particular, the possibility of accessing and hijacking cryptographic devices is also increasing due to the rapid increase in usage of these devices. Therefore, research on cryptographic technologies that can provide a safe environment even in resource-constrained environments has been actively conducted. Among them, there are increasing security issues of side-channel analysis for devices due to their physical accessibility. The lightweight block cipher PIPO was recently proposed in ICISC 2020 to address these issues. The PIPO has the characteristic of providing robust security strength while having less overhead when using the side-channel analysis countermeasures. A differential fault attack is a type of side-channel analysis that induces fault in cryptographic operations and utilizes difference information that occurs. Differential fault attacks on the PIPO have not yet been studied. This paper proposed a single-bit flip-based differential fault attack on the lightweight block cipher PIPO for the first time. We show that simulations enable the recovery of the correct secret key with about 98% probability through 64 fault ciphertexts. Therefore, the PIPO does not provide security against differential fault attacks. When using the PIPO cipher on IoT devices, designers must apply appropriate countermeasures against fault injection attacks

On the IND-CCA1 Security of FHE Schemes

Fully homomorphic encryption (FHE) is a powerful tool in cryptography that allows one to perform arbitrary computations on encrypted material without having to decrypt it first. There are numerous FHE schemes, all of which are expanded from somewhat homomorphic encryption (SHE) schemes, and some of which are considered viable in practice. However, while these FHE schemes are semantically (IND-CPA) secure, the question of their IND-CCA1 security is much less studied, and we therefore provide an overview of the IND-CCA1 security of all acknowledged FHE schemes in this paper. To give this overview, we grouped the SHE schemes into broad categories based on their similarities and underlying hardness problems. For each category, we show that the SHE schemes are susceptible to either known adaptive key recovery attacks, a natural extension of known attacks, or our proposed attacks. Finally, we discuss the known techniques to achieve IND-CCA1-secure FHE and SHE schemes. We concluded that none of the proposed schemes were IND-CCA1-secure and that the known general constructions all had their shortcomings.publishedVersio

Changing of the Guards: a simple and efficient method for achieving uniformity in threshold sharing

Since they were first proposed as a countermeasure against differential power analysis (DPA) in 2006, threshold schemes have attracted a lot of attention from the community concentrating on cryptographic implementations. What makes threshold schemes so attractive from an academic point of view is that they come with an information-theoretic proof of resistance against a specific subset of side-channel attacks: first-order DPA. From an industrial point of view they are attractive as a careful threshold implementation forces adversaries to DPA of higher order, with all its problems such a noise amplification. A threshold scheme that offers the mentioned provable security must exhibit three properties: correctness, incompleteness and uniformity. A threshold scheme becomes more expensive with the number of shares that must be implemented and the required number of shares is lower bound by the algebraic degree of the function being shared plus 1. Defining a correct and incomplete sharing of a function of degree d in d+1 shares is straightforward. However, up to now there is no generic method to achieve uniformity and finding uniform sharings of degree-d functions with d+1 shares is an active research area. In this paper we present a simple and relatively cheap method to find a correct, incomplete and uniform d+1-share threshold scheme for any S-box layer consisting of degree-d invertible S-boxes. The uniformity is not implemented in the sharings of the individual S-boxes but rather at the S-box layer level by the use of feed-forward and some expansion of shares. When applied to the Keccak-p nonlinear step Chi, its cost is very small