In October 2021, an assistant U.S. attorney issued a subpoena to Signal demanding that the messaging app hand over information about one of its users. Based on a phone number, the federal prosecutors were asking for the user’s name, address, correspondence, contacts, groups, and call records to assist with an FBI investigation. Two weeks later, the American Civil Liberties Union responded on behalf of Signal with just two pieces of data: the date the target Signal account was created, and the da...