I'll bet it was Telegram. They have a distributed network, and the FBI managed to convince the jurisdiction(s) where those keys are kept to confiscate them. That or Crooks used a brute-forcible password.

EDIT 1: Maybe this the actual reason the CEO of Telegram was arrested in France.

EDIT 2: Maybe his Telegram accounts prove that he was part of a larger plot to assassinate Donald Trump. Perhaps they were so desperate to destroy that information that they arrested the CEO to get him to order the company to hand the keys over, i.e. rubber-hose cryptanalysis.

I'll bet it was Telegram. They have a distributed network, and the FBI managed to convince the jurisdiction(s) where those keys are kept to confiscate them. That or Crooks used a brute-forcible password.

EDIT: Maybe this the actual reason the CEO of Telegram was arrested in France.

I'll bet it was Telegram. They have a distributed network, and the FBI managed to convince the jurisdiction(s) where those keys are kept to confiscate them. That or Crooks used a brute-forcible password.