A warrant alone, very likely not. A court order from a judge (slightly different than a warrant), possibly not nut it's not exactly a well tread area of legislation/law. It would probably run afoul of the first amendment given some readings, but it would have to be tested in court and would likely be argued that requiring a backdoor via some law doesn't cause compelled speech or that making that backdoor isn't protected speech etc. It's a relatively new area to be explored.