Abstract
Cryptosystems are one of the most important tools for information security, and symmetric-key ciphers are widely used. Cryptographers have developed and applied various cryptanalysis techniques to guarantee security. If no one can attack a symmetric-key cipher, the cipher is regarded as secure. In other words, it is possible that a symmetric-key cipher will suddenly be broken. In this article, we introduce the history of the creation and destruction of symmetric-key ciphers. We also review a new cryptanalytic tool that was used to theoretically break the symmetric-key cipher MISTY1.