A warrant canary is a method used by a service provider to inform its users that the provider has not been served with a secret government subpoena. Such subpoenas, including those covered under the USA Patriot Act, provide criminal penalties for revealing 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 inform users of the existence of a subpoena passively, without violating any laws.
The idea of using negative pronouncements to thwart the secrecy provisions of court orders and secret warrants (now called national security letters) 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. 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."
- "Re: ISP Utilty To Cypherpunks? Yahoo! Groups". Tech.groups.yahoo.com. October 31, 2002. Retrieved 2013-06-13.
- West, Jessamyn (2002). "Five Technically Legal Signs for Your Library". Librarian.net : avoiding the PATRIOT Act since 2001. Archived from the original on 2002-12-18. Retrieved 2013-11-14.
- Doctorow, Cory (September 9, 2013). "How to foil NSA sabotage: use a dead man's switch - Technology". The Guardian (UK). Retrieved 2013-11-14.
- "rsync.net Warrant Canary". rsync.net. Retrieved June 12, 2013.
- Kozubik, John (August 6, 2010). "The Warrant Canary in 2010 and Beyond". Blog.kozubik.com. Retrieved 2013-06-13.
- Farivar, Cyrus (5). "Apple takes strong privacy stance in new report, publishes rare “warrant canary”". ArsTechnica.com. Retrieved 5 November 2013.
- "Report on Government Access Requests". Apple.com. November 5, 2013. Retrieved 2013-11-15.
- "Transparency @ Lookout". Lookout.com. Retrieved 2013-11-05.
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