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A canary trap is a method for exposing an information leak by giving different versions of a sensitive document to each of several suspects and seeing which version gets leaked. It could be one false statement, to see whether sensitive information gets out to other people as well. Special attention is paid to the quality of the prose of the unique language, in the hopes that the suspect will repeat it verbatim in the leak, thereby identifying the version of the document.

The term was coined by Tom Clancy in his novel Patriot Games,[1][non-primary source needed] although Clancy did not invent the technique. The actual method (usually referred to as a barium meal test in espionage circles) has been used by intelligence agencies for many years. The fictional character 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.[2]

Known canary trap cases

Following the troubled production of Star Trek: The Motion Picture in the late 1970s, Paramount Pictures effectively replaced Gene Roddenberry as producer of further movies in the franchise with Harve Bennett. Roddenberry was retained as an "executive consultant", due to the high regard the series' fans held him in; while he had little real authority he was still kept involved in the creative process. The fans often complained about particular plot developments proposed for the films, such as the death of Spock in Star Trek II, that Roddenberry had opposed. So, before any drafts of the screenplay for Star Trek III: The Search for Spock were circulated, Bennett arranged for each individual copy to have subtle clues distinguishing it from the others. Shortly after Roddenberry opposed the destruction of the Enterprise at the climax of that film, fans began to complain to Paramount and Bennett. He found that a leaked copy of the script was the one given to Roddenberry, but was unable to do anything about it.[3]

After a series of leaks at Tesla Motors in 2008, CEO Elon Musk reportedly sent slightly different versions of an e-mail to each employee in an attempt to reveal potential leakers. The e-mail was disguised as a request to employees to sign a new non-disclosure agreement. The plan was undermined when the company's general counsel forwarded his own unique version of the e-mail with the attached agreement. As a result, Musk's scheme was realized by employees who now had a safe copy to leak.[4]

In October 2019, British celebrity Coleen Rooney used the technique to identify who was leaking information from her private Instagram stories to tabloid newspaper The Sun by posting fake stories which were blocked to all but one account. When these details appeared in the press, she publicly identified the leaks as coming from the account of Rebekah Vardy, wife of footballer Jamie Vardy. The subsequent libel trial became known as the Wagatha Christie case.[5][6]

In December 2020, Andrew Lewer, a Member of Parliament and Parliamentary Private Secretary in the UK government, was fired after a canary trap in the form of a letter reminding staff not to leak was published on the website Guido Fawkes.[7]

Barium meal test

According to the book Spycatcher[8] by Peter Wright (published in 1987), the technique is standard practice that has been used by MI5 (and other intelligence agencies) for many years, under the name "barium meal test". A barium meal test is more sophisticated than a canary trap because it is flexible and may take many different forms. However, the basic premise is to reveal a supposed secret to a suspected enemy (but nobody else) then monitor whether there is evidence of the fake information being utilised by the other side. For example, a suspected double agent could be offered some tempting "bait": e.g., be told that important information was stored at a dead drop site. The fake dead drop site could then be periodically checked for signs of disturbance. If the site showed signs of being disturbed (for instance, in order to copy microfilm stored there), then this would confirm that the suspected enemy really was an enemy, i.e., a double agent.

Embedding information

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:

In popular culture

See also


  1. ^ Clancy, Tom (4 September 2018). Patriot games. ISBN 9780440001034. OCLC 1044632177.
  2. ^ Gaines, Cork. "The NBA Used an Espionage Trick Known as 'Canary Trap' to Catch Teams Leaking Info to the Media". Business Insider. Retrieved 2019-10-25.
  3. ^ Engel, Joel (1994). Gene Roddenberry: The Myth and the Man Behind Star Trek. Hyperion Books. pp. 210–11. ISBN 0786860049.
  4. ^ Owen Thomas (2009). "Tesla CEO in Digital Witch Hunt". Gawker Media. Archived from the original on 2013-10-20. Retrieved 2013-11-16.
  5. ^ Rosseinsky, Katie (2019). "Coleen Rooney accuses Rebekah Vardy's Instagram account of leaking stories to the press". Evening Standard. Retrieved 2019-10-09.
  6. ^ Read, Max (2019-10-09). "Coleen Rooney, Instagram Spycatcher". Intelligencer. Retrieved 2022-07-29.
  7. ^ Bland, Archie (18 December 2020). "Ministerial aide sacked after leaking of letter warning MPs not to leak to media". The Guardian. Retrieved 18 December 2020.
  8. ^ Wright, Peter, 1916–1995. (1989). Spycatcher. Mandarin. ISBN 1863300007. OCLC 27626618.((cite book)): CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  9. ^ Zach Aysan. "Zero-Width Characters - Invisibly fingerprinting text".