Recently, Ashur and Liu introduced the Rotational-XOR-difference approach which is a modification of rotational cryptanalysis, for an ARX cipher Speck (Ashur and Liu, 2016). In this paper, we apply the Rotational-XOR-difference (RXD) approach to a non-ARX cipher Simon and evaluate its security. First, we studied how to calculate the probability of an RXD for bitwise AND operation that the round function of Simon is based on unlike Speck is on modular addition. Next, we prove that two RXD trails can be connected such that it becomes possible to construct a boomerang/rectangle distinguisher similar to the case using differential characteristics. Finally, we construct related-key rectangle distinguishers for round-reduced versions of Simon with block lengths of 32, 48, and 64, and we suggest a five- or six-round key recovery attack. To our knowledge, it is the first attempt to apply the notion of rotational cryptanalysis for a non-ARX cipher. Although our attack does not show the best results for Simon thus far, the attempt here to define and apply a new cryptanalytic characteristic is meaningful, and we expect further improvements and applications to other ciphers to be made in subsequent studies.

In this article, we present implementations for Addition, Rotation, and eXclusive-or (ARX)-based block ciphers, including LEA and HIGHT, on IoT devices, including 8-bit AVR, 16-bit MSP, 32-bit ARM, and 32-bit ARM-NEON processors. We optimized 32-/8-bitwise ARX operations for LEA and HIGHT block ciphers by considering variations in word size, the number of general purpose registers, and the instruction set of the target IoT devices. Finally, we achieved the most compact implementations of LEA and HIGHT block ciphers. The implementations were fairly evaluated through the Fair Evaluation of Lightweight Cryptographic Systems framework, and implementations won the competitions in the first and the second rounds.

The recently proposed file-injection type attacks are highlighting the importance of forward security in dynamic searchable symmetric encryption (DSSE). Forward security enables to thwart those attacks by hiding the information about the newly added files matching a previous search query. However, there are still only a few DSSE schemes that provide forward security, and they have factors that hinder efficiency. In particular, all of these schemes do not support actual data deletion, which increments both storage space and computational complexity. In this paper, we design and implement a forward secure DSSE scheme with optimal search and update complexity, for both computation and communication point of view. As a starting point, we propose a new, simple, theoretical data structure, called dual dictionary that can take advantage of both the inverted and the forward indexes at the same time. This data structure allows to delete data explicitly and in real time, which greatly improves efficiency compared to previous works. In addition, our scheme provides forward security by encrypting the newly added data with fresh keys not related with the previous search tokens. We implemented our scheme for Enron email and Wikipedia datasets and measured its performance. The comparison with Sophos shows that our scheme is very efficient in practice, for both searches and updates in dynamic environments.