Perhaps predictably, the letter didn't sit well on the law enforcement side of the encryption debate, which has been going on in Washington DC for months now, ever since Apple announced that data stored on the new iPhone would be encrypted by default and inaccessible even to Apple.

At an event on Wednesday, according to a transcript, FBI Director James Comey said that he "frankly" found the letter "depressing."

"I read this letter and I think, 'Either these folks don't see what I see or they're not fair-minded,'" he said. "And either one of those things is depressing to me."

"'Either these folks don't see what I see or they're not fair-minded."

Comey has been the most outspoken critic of Apple's decision, repeatedly asking tech companies to come up with a solution—hinting that otherwise he'll force them to—so that the FBI and cops don't face a situation in which they can't access key evidence during investigations, a problem the FBI calls "going dark."