Patent ID: 7979731

Claim:
A time authentication device for authenticating a target clock included in a target device, the time authentication device comprising: a clock unit operable to measure a time; a storage unit operable to store a first time and a second time, the first time being measured by the target device and acquired from the target device in response to a first request to the target device to send a time, and the second time being measured by the clock unit relatively to the first request; an acquiring unit operable to acquire a third time and a fourth time, the third time being measured by the target device and acquired from the target device in response to a second request to the target device to send a time, and the fourth time being measured by the clock unit relatively to the second request; a judging unit operable to judge, based on the first time, the second time, the third time, and the fourth time, whether a difference between a time measured by the target clock and a time measured by the clock unit falls within a permissible range; and an output unit operable to output an authentication result indicating that the target clock is valid if the difference is judged to fall within the permissible range, and indicating that the target clock is invalid if the difference is judged to fall outside the permissible range.