Symmetric-key cryptography serves as a security infrastructure of digital societies. In particular, the importance of authenticated encryption (AE), which provides the confidentiality and authenticity of communication, has been widely recognized. On the other hand, since an AE scheme is generally costlier than plain encryption schemes, there is a growing need for lightweight AE suitable for use in constrained environments. With this background, the National Institute of Standards and Technology (NIST) of the United States conducted a standardization project for lightweight AE and selected Ascon as the sole winner in 2023. In this paper, we outline the specifications, security, and implementation aspects of Ascon.

A radio train control system is constructed by integrating safety control and information transmission functions. In the communication channels of train control systems, LCX (leaky coaxial cable) and space waves are used, both of which are private networks installed by railway operators. However, the construction, operation, and maintenance of these networks require significant costs. In recent years, owing to the decline in the working-age population, labor shortages in the railway industry have become more pronounced, increasing the demand for equipment reduction and maintenance simplification in information transmission infrastructure as well. In this paper, we outline the process of achieving functional separation and the reduction in the number of private networks used in train control systems by utilizing general-purpose devices and public communication networks. Furthermore, we discuss a train control system that takes into account the stability of communication transmission paths according to railway trackside equipment.