Secret ink hides full text of The Wonderful Wizard of Oz in a letter

Ink laced with molecules that can store data has been used to write a letter containing a hidden, encoded message – the text of the novel The Wonderful Wizard of Oz  

Technology 20 July 2022

A letter that contained a secret message in the ink

Ink containing encrypted data (left) was used to write this letter (right)

Adapted from ACS Central Science 2022

Ink containing polymers that can store data has been used to write a letter containing a hidden message.

Eric Anslyn at the University of Texas at Austin and his colleagues have developed a technique that involves steganography – the practice of hiding one message inside another.

The team generated a 256-character cipher key to encrypt and decrypt files using the Advanced Encryption Standard (AES), a common cryptography method. The cipher key was then encoded into eight oligourethanes, a type of polymer.


“Because they’re a polymer with a very specific sequence, the units along that sequence can carry a sequence of information, just like any sentence carries information in the sequence of letters,” says Anslyn.

Each polymer was made up of 10 smaller compounds called monomers. The middle eight monomers hold the details of the key, with one monomer on each side acting as the key’s synthesiser and decoder.

The polymers were then mixed with isopropanol, glycerol and soot to make an ink. Using the ink, some of the researchers wrote a letter and then sent it to another person on the team. The group then extracted a sample of the ink and used the cipher key to unlock the hidden message: the entire text of the novel The Wonderful Wizard of Oz by L. Frank Baum.

“The idea of writing a message but the real, hidden message is contained in the molecular structure of the ink is fascinating, although maybe not the most practical method,” says Alan Woodward at the University of Surrey, UK. Woodward points out that the use of AES would mean that the key for encrypting and decrypting the code would still need to be passed securely between the sender and recipient.

For Anslyn, the ability to hide information is secondary. His main goal is storing data. The information density within molecules in polymers, which include DNA, is higher than it would be through encoded magnetic spots on a hard disc.  “The information density is mind-boggling,” he says.

Journal reference: ACS Central Science , DOI: 10.1021/10.1021/acscentsci.2c00460

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