UK Researchers Create Perfectly Secure Digital Communications

A team of researchers from the University of Oxford – working in close collaboration with Carnegie Mellon University – claims to have made a breakthrough to enable “perfectly secure” hidden digital communications for the first time by tackling some of the flaws with steganography via a new computer algorithm.

For those who may be unfamiliar, steganography is the practice of hiding sensitive information inside innocuous content (e.g. hiding a Shakespeare poem inside an AI-generated image of a cat). Steganography differs from cryptography because the sensitive information is concealed in such a way that this obscures the fact that something has been hidden.

However, steganography is not perfect, meaning that individuals who use these methods are still at risk of being detected. This is because previous steganography algorithms would subtly change the distribution of the innocuous content, which could be uncovered if you went looking for it with the right tools.

The team tackled this by using recent breakthroughs in information theory, specifically minimum entropy coupling, which allows one to join two distributions of data together such that their mutual information is maximised, but the individual distributions are preserved.

In other words, when applied, this meant there was no “statistical difference” between the distribution of the innocuous content and the distribution of content that encodes sensitive information. The new algorithm also showed up to 40% higher encoding efficiency than previous steganography methods across a variety of applications, “enabling more information to be concealed within a given amount of data.”

Dr Christian Schroeder de Witt (University of Oxford), Co-lead author, said:

“Our method can be applied to any software that automatically generates content, for instance probabilistic video filters, or meme generators. This could be very valuable, for instance, for journalists and aid workers in countries where the act of encryption is illegal.

However, users still need to exercise precaution as any encryption technique may be vulnerable to side-channel attacks such as detecting a steganography app on the user’s phone.”

The development of such an algorithm could also have implications for other areas, such as improved data compression and storage. On this point, it’s worth noting that the team has filed a patent for the algorithm, but they “intend to issue it under a free licence to third parties for non-commercial responsible use.” An “inefficient implementation” of their method has also been open-sourced on Github, but we don’t have the link.

The paper – Perfectly Secure Steganography using Minimum Entropy Coupling – can be found on arXiv.