| 摘要 |
PROBLEM TO BE SOLVED: To allow the system to have provision for even a re-transmission attack by revising an encryption key and a decoding key in use on each occasion and conducting user authentication between a terminal equipment and a center without using a 2-way protocol. SOLUTION: A new key set generating means 12 of a terminal 1 has lots of encryption keys and decoding keys and one set is selected at random on authentication request. An encryption key storage means 13 stores an encryption key AK' selected previously, an encryption means 15 encrypts a message consisting of a user identifier YID, a password PW, a terminal identifier TID and a decoding key FK selected this time is encrypted by using the key AK' at an encryption means 15 and a plane text TID is added to the encrypted message and the resulting message is transmitted. A decoding key storage means 25 in a center 2 stores the decoding key FK' sent at a preceding time for each TID, a decoding means 22 decodes the message by using the FK' acquired at the TID separated by the terminal ID separate means 21, the coincidence between the TID sent in a plain text and the decoded TID is confirmed, the user is authenticated and the encryption key storage means 13 is updated by using the decoding key FK this time. |
