BLOCK CIPHERING METHOD AND DECODING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a block ciphering method and a decoding method by which the original data can hardly be guessed at the time of making large data into a block and ciphering them. SOLUTION: The ciphering stage of input data is constituted of at least two stages. Data is ciphered by using a password sentence block link mode in the block unit of prescribed byte length in the respective ciphering stages. In the initial ciphering stage, a fixed initialization vector which does not depend on input data is used and the ciphering result of one block in the previous ciphering stage is used as the initialization vector in the next and subsequent ciphering stages.