Abstract
An apparatus and method produce a videotape or other recording that cannot be pre- or post-dated, nor altered, nor easily fabricated by electronically combining pre-recorded material. In order to prevent such falsification, the camera or other recording apparatus periodically receives certifiably unpredictable signals ("challenges") from a trusted source, causes these signals to influence the scene being recorded, then periodically forwards a digest of the ongoing digital recording to a trusted repository. The unpredictable challenges prevent pre-dating of the recording before the time of the challenge, while the storage of a digest prevents post-dating of the recording after the time the digest was received by the repository. Meanwhile, the interaction of the challenge with the evidence being recorded presents a formidable obstacle to real-time falsification of the scene or system, forcing the would-be falsifier to simulate or render the effects of this interaction in the brief time interval between arrival of the challenge and archiving of the digest at the repository.