A warrant canary is a method by which a communications service provider informs its users that the provider has not been served with a secret United States government subpoena. Secret subpoenas, including those covered under 18 U.S.C. §2709(c) of the USA Patriot Act, provide criminal penalties for disclosing the existence of the warrant to any third party, including the service provider's users. A warrant canary may be posted by the provider to inform users of dates that they have not been served a secret subpoena. If the canary has not been updated in the time period specified by the host, users are to assume that the host has been served with such a subpoena. The intention is to allow the provider to warn users of the existence of a subpoena passively, without disclosing to others that the government has sought or obtained access to information or records under a secret subpoena.
United States secret subpoenas or national security letters originated in the 1986 Electronic Communications Privacy Act to be used only against those suspected of being agents of a foreign power. This was revised in 2001 under the Patriot Act so that secret subpoenas can be used against anyone who may have information deemed relevant to counter-intelligence or terrorism investigations. The idea of using negative pronouncements to thwart the nondisclosure requirements of court orders and served secret warrants was first proposed by Steven Schear on the cypherpunks mailing list, mainly to uncover targeted individuals at ISPs. It was suggested for use by public libraries in 2002 in response to the USA Patriot Act.
The first commercial use of a warrant canary was by rsync.net. In addition to a digital signature, they provide a recent news headline as proof that the warrant canary was recently posted as well as mirroring the posting internationally.
On November 5, 2013, Apple became the most prominent company to publicly state that it had never received an order for user data under Section 215 of the Patriot Act. On September 18, 2014, GigaOm reported that the warrant canary statement did not appear anymore in the next two Apple Transparency Reports, covering July–December 2013 and January–June 2014. Tumblr also included a warrant canary in the transparency report that it issued on February 3, 2014. The online cloud service Spider Oak implemented an encrypted warrant canary that publishes an "All Clear!" message every 6 months. Three PGP signatures from geographically distributed signers must sign each message — so if a government agency forced SpiderOak to update the page, they would need to enlist the help of all three signers.
Previously, mobile security company Lookout had stated that it had not received any national security letters and had "not been required by a FISA court to keep any secrets that are not in this transparency report."
- Animal sentinel
- Patriot Act, Title V, National security authorities
- WikiLeaks-related Twitter subpoenas
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- Eunice Moscoso (August 17, 2003), "Subpoenas Fly In Hunt For Hidden Terrorists", Palm Beach Post: 1A
- Shaun Waterman (September 30, 2004), "Ashcroft: U.S. will appeal terror-law ruling", United Press International, retrieved January 3, 2014
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- "Transparency @ Lookout". Lookout.com. Retrieved 2013-11-05.
- "Provide a "warrant canary" for the TextSecure server". Github.com. Retrieved 2014-07-23.
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