There isn't a valid warrant in this case though: instead there's a writ (aka an order by the government) under the All Writs Act. This act allows the government

There isn't a valid warrant in this case though: instead there's a writ (aka an order by the government) under the All Writs Act. This act allows the government to compel a person/company to do something when there isn't any specific law on the books for that particular situation. However, the writ in question is to compel Apple to write a new version of the OS (not to hand over keys, not to hand over data in their possession, not to provide technical support to the FBI - all of which are things Apple has done when presented with a valid warrant). From Apple's motion to vacate: "In the section of CALEA entitled “Design of features and systems configurations,” 47 U.S.C. § 1002(b)(1), the statute says that it “does not authorize any law enforcement agency or officer — (1) to require any specific design of equipment, facilities, services, features, or system configurations to be adopted by any provider of a wire or electronic communication service, any manufacturer of telecommunications equipment, or any provider of telecommunications support services. (2) to prohibit the adoption of any equipment, facility, service, or feature by any provider of a wire or electronic communication service, any manufacturer of telecommunications equipment, or any provider of telecommunications support services." So the writ appears to be in direct contradiction to other law, which would make it an invalid use of the All Writs Act.