Of course, as the indictment also makes clear, the special counsel has already managed to get its hands on plenty of Mr. Stone’s communications by other means — but one seeming exception jumps out. In a text exchange between Mr. Stone and a “supporter involved with the Trump Campaign,” Mr. Mueller pointedly quotes Mr. Stone’s request to “talk on a secure line — got WhatsApp?” There the direct quotes abruptly end, and the indictment instead paraphrases what Mr. Stone “subsequently told the supporter.” Though it’s not directly relevant to his alleged false statements, the special counsel is taking pains to establish that Mr. Stone made a habit of moving sensitive conversations to encrypted messaging platforms like WhatsApp — meaning that, unlike ordinary emails, the messages could not be obtained directly from the service provider.

The clear implication is that any truly incriminating communications would have been conducted in encrypted form — and thus could be obtained only directly from Mr. Stone’s own phones and laptops. And while Mr. Stone likely has limited value as a cooperating witness — it’s hard to put someone on the stand after charging them with lying to obstruct justice — the charges against him provide leverage in the event his cooperation is needed to unlock those devices by supplying a cryptographic passphrase.