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A warrant canary is a method by which a communications service provider aims to inform its users that the provider has not been served with a secret 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. Warrant canaries have been found to be legal by the United States Justice Department, so long as they are passive in their notifications. 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. Australia outlawed the use of a certain kind of warrant canary in March 2015, making it illegal for a journalist to "disclose information about the existence or non-existence" of a warrant issued under new mandatory data retention laws. It is unlikely a journalist could give a correct canary in this situation anyway, as under this legislation the agency obtaining the warrant is not compelled to inform the journalist of the warrant. == Usage == The first commercial use of a warrant canary was by the tech firm Wickr which specializes in secure private messaging. Wickr's canary informs users that no government orders or investigations have been initiated, and, should this change, the canary will be altered. Another early tech firm to adopt warrant canaries was rsync.net. In addition to a digital signature, they provide a recent news headline as proof that the warrant canary was recently posted〔(【引用サイトリンク】title=rsync.net Warrant Canary )〕 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."〔(【引用サイトリンク】title=Transparency @ Lookout )〕 In July 2014, US security researcher Moxie Marlinspike stated that "every lawyer we've spoken to has confirmed that (warrant canary ) would not work" for the TextSecure server. In September 2014, Marlinspike added to this by stating that "()f it's illegal to advertise that you've received a court order of some kind, it's illegal to intentionally and knowingly take any action that has the effect of advertising the receipt of that order. A judge can't force you to do anything, but every lawyer I've spoken to has indicated that having a "canary" you remove or choose not to update would likely have the same legal consequences as simply posting something that explicitly says you've received something."〔 Canarywatch was founded to provide a compiled list of all companies providing warrant canaries. Its mission is to provide prompt updates of any changes in a canary's state. It is often difficult for users to ascertain a canary's validity on their own and thus Canarywatch provides a simple display of all active canaries and any blocks of time that they were not active. In March 2015, after Australia outlawed warrant canaries, computer security and privacy specialist Bruce Schneier wrote in a blog post that "()ersonally, I have never believed (canaries ) would work. It relies on the fact that a prohibition against speaking doesn't prevent someone from not speaking. But courts generally aren't impressed by this sort of thing, and I can easily imagine a secret warrant that includes a prohibition against triggering the warrant canary. And for all I know, there are right now secret legal proceedings on this very issue." 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Warrant canary」の詳細全文を読む スポンサード リンク
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