Of course, if it's is just signed-frame video, "prior art" doesn't begin to describe 



Science Daily

Source : 
Johns Hopkins University 

Date : 

Johns Hopkins APL Creates System To Detect Digital Video Tampering 

The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., has 
opened the door to using reliable digital video as evidence in court by developing a 
system that identifies an attempt to alter digital video evidence. 

"It's not too hard to make changes to digital video," says Tom Duerr, APL's project 
manager. "But our system quickly and conclusively detects any alterations made to the 
original tape." For the past two years, Duerr has led development of the project for 
the United States Postal Inspection Service. 

"We're satisfied that our system can accurately detect tampering and now we're 
building a working prototype that can be attached to a camcorder," says Nick Beser, 
lead engineer for the project. "Our authenticator provides proof of tampering when the 
human eye can't detect it. You might theorize that a change has been made, but this 
system takes the theory out of that determination." 

The U.S. Postal Inspection Service, the federal law enforcement agency that safeguards 
the U.S. Postal Service, its employees and assets, and ensures the integrity of the 
mail, uses video surveillance and cutting edge technology as investigative tools in 
many of its cases. "We are looking forward to field testing the prototype developed by 
APL," says Dennis Jones, assistant postal inspector in charge of the agency's Forensic 
& Technical Services Division. "Being able to present a certifiable digital recording 
in court in support of our investigative efforts will minimize court challenges over 
the admissibility of such evidence. This system could reinforce the public's 
confidence in the work of law enforcement professionals." 

Securing the System 

The authentication system computes secure computer-generated digital signatures for 
information recorded by a standard off-the-shelf digital video camcorder. While 
recording, compressed digital video is simultaneously written to digital tape in the 
camcorder and broadcast from the camera into the Digital Video Authenticator 
(currently a laptop PC). There the video is separated into individual frames and three 
digital signatures are generated per frame -- one each for video, audio, and 
camcorder/DVA control data -- at the camcorder frame rate. 

Public-key cryptography is used to create unique signatures for each frame. The "keys" 
are actually parameters from mathematical algorithms embedded in the system. Duerr 
says, "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 Digital Video Authenticator'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 generated for the recording make it easy to recognize 
tampering. If a frame has been added it won't have a signature and will be instantly 
detected. If an original frame is altered, the signature won't match the new data and 
the frame will fail verification. The method is so perceptive that tampering with even 
a single bit (an eighth of a byte) of a 120,000-byte video frame is enough to trigger 
an 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. 

When finished, the Digital Video Authenticator is expected to be within the size and 
cost range of consumer-grade digital camcorders. It will be attached to, rather than 
embedded in, a video camera, which allows it to be transferred to different cameras 
when current ones become obsolete. Comparison of signatures with recorded video and 
analysis of the results will be accomplished in separate software that will run on a 
desktop PC. 

Prototype development will include peer review by other researchers and potential 
users and is expected to be completed by 2005. In addition to Postal Inspection 
Service use, the system could serve state and local law enforcement needs and possibly 
corporate and other business venues. 


The Applied Physics Laboratory, a division of The Johns Hopkins University, meets 
critical national challenges through the innovative application of science and 
technology. For more information, visit http://www.jhuapl.edu .

This story has been adapted from a news release issued by Johns Hopkins University. 

R. A. Hettinga <mailto: [EMAIL PROTECTED]>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
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