For as long as there have been secrets, there have been ways to hide those secrets. The Romans had the Caesar cypher, and today we rely on futuristic techniques like quantum cryptography – or the blockchain, which is arguably a step down from Ancient Rome in terms of information security. 

But if you want to be really smart about it, you might not send a secret message at all. The clever thing to do would be to send a normal, non-suspicious message that anybody can read freely … and hide the secrets in plain view.

It’s called steganography, and a new paper, published in the American Chemical Society journal ACS Central Science, describes an unusually whimsical example of the technique: an encrypted message-within-a-message which, when discovered, will take you straight out of Kansas.

“I love the 1939 Judy Garland Movie [The Wizard of Oz], as well as the book,” Eric Anslyn, Professor and Welch Regents Chair in Chemistry at the University of Texas at Austin, told IFLScience. “[So] this is what we chose to encrypt with a 256-bit key.”

The key to that encryption was sent through the mail to a colleague, and the book was successfully revealed. But it wasn’t the message in the letter that was important – it was the ink. 

“Our group makes sequence-defined oligourethanes,” Anslyn explained. 

“We have very easy ways to write them (synthesize) and read them (sequence them),” he told IFLScience. “As with any sequence defined series of symbols (such as the English language), these oligourethanes can carry information.”

And so the team synthesized them to do just that. Using eight oligourethanes – a special type of polymer – they encoded a 256-character key to encrypt and decrypt a digital version of L. Frank Baum’s The Wonderful Wizard of Oz. 

“To store 256 bits of information, we chose to encode a cipher key in hexadecimal (base-16) in a mixture of eight 10-mer [oligourethanes],” explains the paper. “Eight of the 10 monomers encode information … In base-16, each monomer provides a storage density of 4 bits per monomer, thus 32 bits per 10-mer, and overall, 256 bits in the sample.”

Mix these oligourethanes with a little soot, isopropanol, and glycerol, and you’ve got a serviceable ink – all your target reader need do is extract a sample and read off those original polymers.

“The idea of writing a message but the real, hidden message is contained in the molecular structure of the ink is fascinating,” Alan Woodward, professor of Computer Science at the University of Surrey’s Centre for Cyber Security, told New Scientist. “Although [it’s] maybe not the most practical method.” 

On that, Anslyn is in agreement. The next goal for the team will probably not be an encrypted version of The Marvelous Land of Oz, but the development of these ideas for large-scale data storage, he told IFLScience – and the part of the study he’s most proud of wasn’t the encryption, but the methods used to do it.

“The most important scientific breakthrough was the use of mass tags that allow us to sequence eight oligourethanes simultaneously,” he told IFLScience. 

“This is the real advance in the field,” he added. “The encryption key was just a single application that can be envisioned.”