Patent ID: 8522038

Claim:
A method for preventing unauthorized access to a computer system by using an one-time password comprising steps of: inputting an unique user identifier, a valid start time which indicates a valid time when the one-time password takes effect and a valid use duration which indicates a length of a period from using of the password to log on until expiration of the password to a password generator; generating a random number by a random number generation unit; compressing the user identifier, the valid start time, the valid use duration and the random number by a compression unit; encrypting the compressed result of the compression unit to produce an one-time password; entering the one-time password to a computer logon system in the computer system by a user; decrypting the one-time password by a decryption unit; decompressing the result of the decryption unit to get the user identifier, the valid start time and the valid use duration; verifying if the one-time password is valid by comparing the user identifier to the registered identifier, verifying if current time is later than the valid start time, and monitoring if time accumulation user operates with the one-time password has exceeded range of the valid use duration; prompting the user that the logon has failed and locking the computer system if the user identifier is not the same as the registered user identifier in the computer system; prompting the user that the logon has failed and locking the computer system if current time is later than the valid start time; recording the valid start time and valid use duration if the current time is not later than the valid start time; entering the computer system by the user; summing up periods of time during which the user has logged on the computer system with the one-time password to get an actual use time; prompting the user that the valid use duration has expired and locking the computer system if the valid use duration is smaller than the actual use time.