Bacon's cipher

How it works

Francis Bacon described his biliteral alphabet in 1605 and 1623. Each letter is written as five symbols, each a or b: with I and J, and U and V, sharing a code, the 24 letters are the numbers 0 to 23 in five binary digits (A = aaaaa, B = aaaab, C = aaaba). A 26 letter version gives every letter its own code.

Bacon’s point was steganography: the a and b need not be visible as such. Any two kinds of anything work, two typefaces, two sizes, upper and lower case. A harmless cover text five times longer than the secret can carry it in the case of its letters.

As a cipher it is a fixed code with no key, so it protects nothing once it is spotted. What it hides well is the existence of a message.