Earlier this year, Open Whisper Systems was served with a federal subpoena for records on its users, according to documents published today. Prosecutors were seeking data on two suspects who used Signal, an encrypted chat app produced by Open Whisper. Unfortunately for the government, Signal keeps only minimal logs on users, so the vast majority of the requested information was unavailable.

The American Civil Liberties Union, which represented Open Whisper Systems in the fight, has published a number of court filings related to the the request. Portions of the filings are redacted and much about the subpoena is still secret — including the case number, the date it was served, and the details of the underlying case — but it’s clear that the government sought detailed information on the users including subscriber name, payment information, and associated IP addresses.

Filed under gag order

It’s also clear that almost none of that information was ultimately produced. One of the phone numbers named by the government did not correspond to a Signal account, and logs on the other number showed only when the user first signed up for the service and when they most recently logged in.

Crucially, the request was filed under gag order, and Open Whisper was only able to publish the documents after a significant legal fight. That has become standard practice for such requests, although many legal scholars believe widespread use of the tactic presents a threat to free speech.

Open Whisper Systems wrote the encryption software that powers WhatsApp and Allo’s Incognito mode, but all of the associated hardware is run by Facebook and Google, respectively. As a result, many of those apps have different logging practices, and could be vulnerable to such an order. WhatsApp was rumored to have resisted a similar wiretap order earlier this year, although the details of the case are still unknown.