Canary trap

A canary trap is a method for exposing an information leak, which involves giving different versions of a sensitive document to each of several suspects and seeing which version gets leaked.

The term was coined by Tom Clancy in his novel Patriot Games, though the method itself has been in use far longer. The hero, Jack Ryan, describes the technique he devised for identifying the sources of leaked classified documents:

Each summary paragraph has six different versions, and the mixture of those paragraphs is unique to each numbered copy of the paper. There are over a thousand possible permutations, but only ninety-six numbered copies of the actual document. The reason the summary paragraphs are so lurid is to entice a reporter to quote them verbatim in the public media. If he quotes something from two or three of those paragraphs, we know which copy he saw and, therefore, who leaked it.

A refinement of this technique uses a thesaurus program to shuffle through synonyms, thus making every copy of the document unique.

According to the book Spycatcher by Peter Wright, the technique is used by MI5 under the name Barium Meal.

The technique of embedding significant information in a hidden form in a medium has been used in many ways, which are usually classified according to intent:

• Watermarks are used to show that items are authentic and not forged.
• Steganography is used to hide a secret message in an apparently innocuous message, in order to escape detection.
• A canary trap hides information in a document that uniquely identifies it, so that copies of it can be traced.

Appearances in fiction

The canary trap was also used in Clancy's (chronologically) earlier novel, Without Remorse, when a CIA official alters a report given to a senator, revealing an internal leak who was giving information to the KGB.

Barium meals are also administered in Robert Littel's book The Company, and later in the TV short-series with same name.

The technique (not named) was used in the 1970s BBC television serial 1990.

A variation of the canary trap was used in Miami Vice, with various rendezvous dates leaked to different groups.

A Fred Saberhagen Berserker science fiction short story, "The Annihilation of Angkor Apeiron," has a Berserker directed to a star system by an encyclopedia salesman. The salesman is put on trial for treason, but reveals that the encyclopedia article for the star system, with population figures, resources, etc., was a fictitious entry included in the encyclopedia to detect plagiarism; thus the Berserker actually ended up in an empty star system where it ran out of fuel and ceased to be a threat to humanity.

Appearances in media

When distributing Broken to friends, Trent Reznor claims that he watermarked the tapes with dropouts at certain points so that he could identify if a leak would surface.

Screener versions of DVDs are often marked in some way so as to allow the tracking of unauthorised releases to their source.

See also

• Watermark
• Steganography
• Honeypot (espionage)
• Honeytoken
• Fictitious entry
• Traitor tracing
• Trap street

External links

• Fingerprinting gives a good overview of different kinds of canary trap techniques.
• EFF.org DocuColor Tracking Dot Decoding Guide How to read the date, time, and printer serial number from forensic tracking codes in a Xerox DocuColor color laser printout.