The clash between Apple and the FBI is the latest battle in a century-long conflict over the power to keep secrets. The FBI wants Apple to build a “backdoor to the iPhone” so that it can read encrypted data on a locked phone used by one of the San Bernadino attackers.

Apple says such a backdoor would be the equivalent of “a master key, capable of opening hundreds of millions of locks”. Creating such a key, Apple says, would “undermine decades of security advancements”.