The recent rise of end-to-end encrypted messaging apps has given billions of people access to strong surveillance protections. But as one federal watchdog group may soon discover, it also creates a transparency conundrum: Delete the conversation from those two ends, and there may be no record left.
The conservative group Judicial Watch is suing the Environmental Protection Agency under the Freedom of Information Act, seeking to compel the EPA to hand over any employee communications sent via Signal, the encrypted messaging and calling app. In its public statement about the lawsuit, Judicial Watch points to reports that EPA staffers have used Signal to communicate secretly, in the face of an adversarial Trump administration.
But encryption and forensics experts say Judicial Watch may have picked a tough fight. Delete Signal's texts, or the app itself, and virtually no trace of the conversation remains. "The messages are pretty much gone," says Johns Hopkins crypotgrapher Matthew Green, who has closely followed the development of secure messaging tools. "You can’t prove something was there when there’s nothing there."
Signal, like other end-to-end encryption apps, protects messages such that only the people participating in a conversation can read them. No outside observer---not even the Signal server that the messages route through---can sneak a look. Delete the messages from the devices of two Signal communicants, and no other unencrypted copy of it exists.
In fact, Signal's own server doesn't keep record of even the encrypted versions of those communications. Last October, Signal's developers at the non-profit Open Whisper Systems revealed that a grand jury subpoena had yielded practically no useful data. "The only information we can produce in response to a request like this is the date and time a user registered with Signal and the last date of a user's connectivity to the Signal service," Open Whisper Systems wrote at the time. (That's the last time they opened the app, not sent or received a message.)
Even seizing and examining the phones of EPA employees likely won't help if users have deleted their messages or the full app, Green says. They could even do so on autopilot. Six months ago, Signal added a Snapchat-like feature to allow automated deletion of a conversation from both users' phones after a certain amount of time. Forensic analyst Jonathan Zdziarski, who now works as an Apple security engineer, wrote in a blog post last year that after Signal messages are deleted, the app "leaves virtually nothing, so there’s nothing to worry about. No messy cleanup." (Open Whisper Systems declined to comment on the Judicial Watch FOIA request, or how exactly it deletes messages.)
Still, despite its best sterilization efforts, even Signal might leave some forensic trace of deleted messages on phones, says Green. And other less-secure ephemeral messaging apps like Confide, which has also become popular among government staffers, likely leave more fingerprints behind. But Green argues that recovering deleted messages from even sloppier apps would take deeper digging than FOIA requests typically compel---so long as users are careful to delete messages on both sides of the conversation and any cloud backups. "We’re talking about expensive, detailed forensic analysis," says Green. "It’s a lot more work than you’d expect from someone carrying out FOIA requests."
Deleting records of government business from government-issued devices is---let's be clear---illegal. That smartphone scrubbing, says Georgetown Law professor David Vladeck, would blatantly violate the Federal Records Act. "It’s no different from taking records home and burning them," says Vladeck. "They’re not your records, they’re the federal government's, and you’re not supposed to do that."
Judicial Watch, for its part, acknowledges that it may be tough to dig up deleted Signal communications. But another element of its FOIA request asks for any EPA information about whether it has approved Signal for use by agency staffers. "They can’t use these apps to thwart the Federal Records Act just because they don’t like Donald Trump," says Judicial Watch president Tom Fitton. "This serves also as an educational moment for any government employees, that using the app to conduct government business to ensure the deletion of records is against the law, and against record-keeping policies in almost every agency."
Fitton hopes the lawsuit will at least compel the EPA to prevent employees from installing Signal or similar apps on government-issued phones. "The agency is obligated to ensure their employees are following the rules so that records subject to FOIA are preserved," he says. "If they’re not doing that, they could be answerable to the courts."
Georgetown's Vladeck says that even evidence employees have used Signal at all should be troubling, and might warrant a deeper investigation. "I would be very concerned if employees were using an app designed to leave no trace. That's smoke, if not a fire, and it’s deeply problematic," he says.
But Johns Hopkins' Green counters that FOIA has never been an all-seeing eye into government agencies. And he points out that sending a Signal message to an EPA colleague isn't so different from simply walking into their office and closing the door. "These ephemeral communications apps give us a way to have those face-to-face conversations electronically and in a secure way," says Green. "It's a way to communicate without being on the record. And people need that."
