This might be a solution in matters of domestic criminal activity, provided the warrant was served on a party that possessed a copy of the key. In that case they might be able to persuade the key holder to provide access to the encrypted material by presenting it as the preferable alternative to various contempt of court punishments.
Otherwise, they are asking, in principle, for something they never have had in practice: a way to access messages encrypted using methods they do not know and keys that they do not have and which those who do will be reluctant to disclose and possibly unavailable for interrogation and possible punishment. Lack of that capability and its successful circumvention have been a consistent thread in political and military history for several thousand years, probably about since the invention of written communication. It is a "nice to have" but never has been, is not, and probably never will be, a "must have."
Biting the hand that feeds IT
