Miyaji Laboratory

In recent years, information and communication technology has developed rapidly and has been essen- tial for social systems. As deverse information has come to be exchanged, there has been an increased focus on information security. Cryptography is an essential element for maintaining data confidentially, integrity, and availability in information communication. The encryption procedure for symmetric-key cryptography often employs the ARX (Addition-Rotation-XOR) structure, which uses only bitwise ad- dition, cyclic shift, and exclusive disjunction. For ciphers employing this structure, security analysis is performed using differential-linear analysis, which combines differential analysis and linear analysis. In this study, we focus on the linear approximation of ChaCha for stream ciphers in symmetric key cryp- tography, correcting errors in existing papers and showing its validity with respect to generalized linear approximation.