PURPOSE: To reduce the processing time without deteriorating the secrecy of data in the data transmission system between an IC card and a terminal equipment.
CONSTITUTION: A password PIN1 inputted by a carrier of an IC card 12 is ciphered according to a predetermined key data Rd to generate a key data K1. A synthesis text data M1 resulting from adding an additional data CER1 to a text data D1 representing a deposit balance or the like is ciphered according to the key data K1 to generate a ciphered text data ME. The ciphered synthesis text data ME has information comprising the text data D1 and the password PIN1. The ciphered synthesis text data ME is decoded and separated into a text data D2 and an additional data CER2. The separated additional data CER2 is compared with the additional data CER1 stored in advance in the IC card 12. As a result, the adequacy of the correlation PIN1 and the text data D2 is judged. Then the number of times of ciphering/decoding and the number of times of data transmission reception between the terminal equipment 11 and the IC card 12 are reduced to reduce the time required for session.
YORIMOTO GIICHI
YURA AKIYUKI
