SIMON is a lightweight block cipher designed by NSA in 2013. NSA presented the specification and the implementation efficiency, but they did not provide detailed security analysis nor the design rationale. The original SIMON has rotation constants of (1,8,2), and Kölbl et al. regarded the constants as a parameter (a,b,c), and analyzed the security of SIMON block cipher variants against differential and linear attacks for all the choices of (a,b,c). This paper complements the result of Kölbl et al. by considering integral and impossible differential attacks. First, we search the number of rounds of integral distinguishers by using a supercomputer. Our search algorithm follows the previous approach by Wang et al., however, we introduce a new choice of the set of plaintexts satisfying the integral property. We show that the new choice indeed extends the number of rounds for several parameters. We also search the number of rounds of impossible differential characteristics based on the miss-in-the-middle approach. Finally, we make a comparison of all parameters from our results and the observations by Kölbl et al. Interesting observations are obtained, for instance we find that the optimal parameters with respect to the resistance against differential attacks are not stronger than the original parameter with respect to integral and impossible differential attacks. Furthermore, we consider the security against differential attacks by considering differentials. From the result, we obtain a parameter that is potential to be better than the original parameter with respect to security against these four attacks.

For the improvement of software quality and productivity, the author aims at realizing a software development environment to develop software through utilizing the merits of group work. Since networking is necessary for collaborative software development, he has developed a software distributed development environment for collaborative software development. In this environment, discussions about software design are held through a communication network, and the contents of discussions are recorded as software design decisions and decision rationale. One feature of this environment is that the contents of discussions can be recorded in on-line real time and reused without reconstructing the information recorded through this environment. This paper clarifies the essential conditions for actualizing this environment and proposes an information structure model for recording the contents of discussions that actualizes the above-mentioned feature. The effectiveness of the proposed model is proved through an example of its application to software design discussions.