Steganography: An Invincible Form of Secret Communication

Friday - May 19 2023, 03:53 UTC - 1 year ago

The FBI arrested 10 Russian spies near New York City in 2010 which made the public aware of steganography: a way to hide secret messages within harmless-looking messages. A new proof lays out how to achieve perfect security for steganography in machine-generated messages, which can be used for both spies and those trying to get information out of restricted countries.

On June 27, 2010, the FBI arrested 10 Russian spies who lived and worked as American professionals near New York City. The case, which unraveled an intricate system of false identities and clandestine meetings, exposed one of the largest spy networks in the U.S. since the Cold War ended and inspired the show The Americans.

It also brought attention to steganography, a way of disguising a secret message within another message. The New York spies hid their secrets in plain sight, encoding communications within the pixels of seemingly innocuous images posted on publicly available websites. To read them, the recipient had to download an image, translate it into the 1s and 0s of binary code, and know which altered digits, taken in sequence, would spell out the secret.Steganography, which is both an art and a science, differs from the better-known method of secret communication known as cryptography. Where cryptography intentionally conceals the content of a message, transforming it into a tangle of text or numbers, steganography conceals the fact that a secret exists at all. "Steganography hides the presence of the message," said Christian Cachin, a computer scientist and cryptographer at the University of Bern. "If an adversary can detect a hidden message, then the sender has lost the game."As with any method of covert communication, the challenge is how to make it perfectly secure, meaning neither a human nor a machine detector would suspect a message of hiding a secret. For steganography, this has long been a theoretical possibility, but it was deemed impossible to achieve with actual human communications.

The advent of large language models such as ChatGPT suggests a different way forward. While it might be impossible to guarantee security for text created by humans, a new proof lays out for the first time how to achieve perfect security for steganography in machine-generated messages — whether they’re text, images, video or any other media. The authors also include a set of algorithms to produce secure messages, and they are working on ways to combine them with popular apps.

"As we increasingly become a society where it’s very common to interface with AI models, there are increasingly many opportunities to encode secret information in media that people use all the time," said Samuel Sokota, a computer scientist at Carnegie Mellon University who helped develop the new algorithms.

The result comes from the world of information theory, which provides a mathematical framework for understanding communication of all sorts. It’s an abstract and tidy field, in contrast to the complicated messiness of practical steganography. The worlds don’t often overlap, said Jessica Fridrich, a researcher at Binghamton University who studies ways to hide (and detect) data in digital media. But the new algorithms bring them together by satisfying long-standing theoretical criteria for security and suggesting practical applications for hiding messages in machine-generated content. The new algorithms could be harnessed by spies like the New York Russians, but they could also help people trying to get information in or out of countries that prohibit encrypted channels.

Shaved Heads and Other StrategiesThe schemes of steganography, Greek for "covered writing," predate digital media by maddeningly complex methods. Before the dawn of photographic cameras, invisible ink, and "the encryption by obscurity of invisible ink and other substances," Cachin said.