Spy case shines light on steganography

GCN – July 1, 2010

Alleged agents hid messages in plain sight in digital photos

By Trudy Walsh

One of the spy technologies that's come to light in the recently-exposed alleged Russian spy ring is steganography, a word that comes from the Greek for “covered writing.” It’s a way to hide information in plain sight, and has been around since ancient times, in one form or another.

In one example, a Greek named Histaiaeus shaved the head of a slave, tattooed a message on his scalp, and then waited until his hair grew back to send him on his way. The recipients of the message shaved the slave’s head again to see the message. Conspiracy theorists maintain that crop circles are a similar trick—an encoded message from aliens (or pranksters) that disappears once the barley grows back.

Other low-tech steganography methods include knitting encoded messages into sweaters, or encoding messages in print so small that it takes a magnifying glass to read it. Even invisible ink, also used by the accused Russian spy ring, is a form of steganography.

But the digital age has opened up whole new avenues for the practice. The 11 people accused of being part of a Russian espionage ring reportedly inserted text into digital images. Investigators searched the suspects’ hard drives and found drafts of messages embedded in the images.

Because image and audio files tend to be large, they make great hiding places for messages.  In an audio file, steganographic messages are often hidden in the brief silence at the beginning of a song. By comparing the wave signature of a suspected file to a clean copy of the song, you can tell if a message has been inserted.