Steganography, a close cousin of cryptography, is the art of concealing a message within another message. The term was first used by Johannes Trithemius in the 15th century in his book Steganographia (which itself was disguised as a book on magic). In layman’s terms, it’s known as “secret writing,” and part of its allure is that the secret message, or “ghost message,” is hidden in plain sight: The message itself is concealed in an object that does not attract attention, therefore making it an ideal spycraft tool.
The forefather of ghost messages was a clever 16th century Italian cryptographer. Giambattista della Porta was so brilliant at formulating ways to pass along information using secret writing that his research and techniques are still studied in military circles today. His treatise Magia Naturalis (“Natural Magic” in English) was published in 1558 in Naples and contained forward-thinking theories on a variety of scientific subjects, including an important chapter on steganography which caught the attention of the world.
della Porta’s most indelible mark in the practice of steganography was the invention of a way to hide messages inside of eggs, which Nathaniel Sackett demonstrates for Ben Tallmadge in Episode 6, “Mr. Culpeper.” Using a mixture of alum (a common household spice) and vinegar, the sender writes a message on the shell of a hard-boiled egg. On the outside, the egg looks unaltered; however, when the shell is peeled away, the message is exposed on the egg white. della Porta’s invention vaulted the humble egg from breakfast centerpiece to spycraft superfood.
With the rise of steganography came the question of the best “ink” to use when sending ghost messages. Though della Porta was an early champion of alum, many other fluids have been deployed, often depending on what was most accessible at the time. In The Art of Love, Roman poet Ovid referenced lovers using liquid derived from a plant (specifically, the milk of the tithymalus) to send secret messages to one another. A whole host of organic fluids can be used to write ghost messages on paper, including lemon juice, vinegar, milk, oatmeal, onion juice, sweat, saliva, urine, and even diluted blood. Depending on what type of “ink” is used, the message can later be revealed by applying heat or an appropriate chemical, or by viewing the paper under an ultraviolet light.
Whether the message is a dire warning between allies or a secret letter between lovers, steganography has long been a crucial tool for passing along hidden messages without detection. Used effectively, it can be a vital conduit of intelligence, passing information along right in front of the enemy’s eyes without detection.Read More