How To Share Secret Messages in Public Facebook Posts

Doug Bernard | Washington DC

Let’s say you had something you wanted to say; a message for just one or two other people, but secret to everyone else. It’s a fair bet one of the last places you might consider posting that message was anywhere near Facebook, the infamously porous social network.

But you may want to hold that bet until you’ve heard about Secretbook, a new plug-in app that allows you to hide encrypted messages in images you post on Facebook.

The plug-in, an extension available only for Google’s Chrome web browser, is essentially a complex algorithm developed by Owen Campbell-Moore, a computer science student at Oxford University. Messages can be up to 140 characters in length – standard tweet length – and can only be accessed by use of a special key, or password, provided to the chosen recipients.

Robert Beckhusen with the excellent blog “Danger Room” caught up with Campbell-Moore, who has been studying the field of “steganography”, or the craft of concealing messages or images in such a way that hides their existence to all but a chosen few:

“The goal of this research was to demonstrate that JPEG steganography can be performed on social media where it has previously been impossible,” Campbell-Moore tells Danger Room. He says he spent about two months spread out over the last year working on the extension as a research project for the university.

Digital images, composed of millions of bits of data, have long been manipulated to hide information in ways that don’t significantly alter the image’s appearance, at least to the human eye. A problem with using Facebook and other services, however, is that images uploaded to social network are reformatted and compressed, which both alters the original image and the hidden message inside. That would likely turn any secret data into a useless garble.

But Campbell-Moore tells Beckhusen that he re-created Facebook’s compression formula, allowing a user to squeeze the image just as Facebook does at the same time as secreting away the 140-character image. The resulting image, when posted on Facebook, will appear just like any other uploaded photo.

Of course, nothing is foolproof. Photos with large sections of relatively similar or plain images – a white field of snow, say, or a cloudless blue sky – may actually appear altered by Secretbook’s algorithm. And there’s also concern about who might be sending secret messages and what they might say. A friend could add a snarky comment to a family photo as easily as a terrorist could encode a more threatening message.

That’s not a worry, however, for Campbell-Moore:

“A researcher could certainly build a simple system for detecting which images have secret messages hidden in them although they would first require access to all 300+ million photos being uploaded to Facebook every day,” Campbell-Moore says. “Which I suspect even the NSA doesn’t currently have, and performing detection on that scale would be very difficult.”

So the next time you see new photos posted by a friend on Facebook, just remember: they might be saying more than you think.