Digital Video Authenticator
Researchers at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) have developed a system that can accurately detect digital video that has been tampered with. The JHU/APL system is designed to attach to, rather than be embedded in a video system due to the rapid obsolescence of camcorders. The JHU/APL Digital Video Authenticator (DVA) relies on computer generated secure digital signatures on information available from standard off-the-shelf digital video camcorders. When a commercial camcorder records an event, compressed digital video is simultaneously written to digital tape and broadcast from the camera into the DVA. There the video is separated into individual frames and three digital signatures per frame are generated - one for each video, audio, and camcorder/DVA control data - at the camcorder frame rate. JHU/APL researchers use a two-key form of public-key cryptography to create unique signatures for each frame. The "keys" are actually parameters from mathematical algorithms embedded in the system. The keys, signature, and original data are mathematically related in such a way that if any one of the three is modified, the fact that a change took place will be revealed in the verification process. One key, called a "private" key, is used to generate the signatures and is destroyed when the recording is complete. The second, a "public" key, is used for verification. To provide additional accountability, a second set of keys is generated that identifies the postal inspector who made the recording. This set of keys is embedded in a secure physical token that the inspector inserts into the system to activate the taping session. The token also signs the DVA's public key, ensuring that the public key released with the video signatures was created by the inspector and can be trusted. The signatures that are applied to the tape make it easy for the authenticator to recognize tampering. If a frame has been added, it won't have a signature and the system will instantly detect that. If an original frame is altered, the signature won't match the new data and the frame will fail verification. The system is so perceptive that tampering with even a single bit (an eighth of a bite) of a 120,000-byte video frame is enough to trigger an error alert. After an event is recorded, the signatures and the signed public key are transferred to a removable storage device and secured along with the original tape in case the authenticity of a tape is challenged.
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