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."

End-to-Dead-End

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.