Trusted Camera - Online Version
This version uses a trusted time service to add verifiable timestamps
to the signed images.
A "trusted time service" uses a accurate clock, such as GPS or atomic clock
corrected, and a digital signer to provide verifiable timestamps.
The time service guarantees that the image was signed at time T, hence it must
have been taken prior to that time. In the absence of tampering with the camera, it can be
stated that the image was taken shortly before time T. For greater timekeeping accuracy,
the camera may obtain transmission-delay corrected time from the time service using a
method such as NTP, and add it to the camera metadata, or an onboard clock may be used and
- The camera takes an image and generates a checksum
- Metadata such as frame count, GPS location, title etc. is added to the checksum and the
composite checksum is sent to the time service
- The time service generates a timestamp, combines
it with the checksum, signs it and returns it to the camera
- The camera signs the composite timestamp and stores it with the image
An example of a
commercial timestamping service may be found at Evertrust.net
For still images, a checksum may be sent to the timestamp service for each image.
For video, checksums for a group of frames (a second, or a minute) may be sent for timestamping, or
only one frame in 100 may be timestamped and times for other frames may be interpolated. The signature
object for a video file is thus more complex than for a still image file.
The camera may be used to
created a timestamped image of a printed photograph or delayed video,
and thus make it appear that the event took
place later than it in fact did.
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