🥓Security

Baconian Cipher, 5-Bit A/B Groups

Encodes each letter as a group of five A and B symbols in Bacon's 24-letter alphabet, where I shares a code with J and U shares one with V.

Text

Codificado

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Bacon's cipher: five bits before bits existed

Francis Bacon described in 1605 a system in which each letter becomes a sequence of five symbols of two kinds, which he called a and b. With five positions and two options there are 32 combinations — enough for the 26 letters. It is, in practice, a five-bit binary encoding, three and a half centuries before the term existed.

Paste the text and the page returns the groups of five letters. The clever part of the system is not the table but what Bacon proposed doing with it: the two symbols need not be letters. They can be two typefaces in the same text, upper and lower case, or any pair of discreet variations — and then the message hides inside another apparently innocent text.

That makes Bacon's cipher less a cipher than a method of steganography: the goal is not scrambling the content, it is hiding that content exists. In this classic version I and J share a code, as do U and V, which reduces the table to 24 entries — a reflection of the alphabet of the day, which did not distinguish those pairs.

Frequently asked questions

Why do I and J share a code?

Because in the seventeenth-century Latin alphabet they were the same letter, as were U and V. Bacon's original table has 24 entries for that reason. Modern versions exist with 26 distinct entries, using the combinations that were left over.

How is the message hidden inside another text?

By choosing two discreet variations to stand for a and b and applying them letter by letter across the cover text: two slightly different typefaces, the presence or absence of italics, upper and lower case. Anyone who does not know what to look for reads the cover text without noticing a thing.

Can it decode here?

This page only encodes. The inverse is straightforward once you already have the groups of five — just consult the table — but the genuinely interesting case, extracting a message from a cover text, depends on knowing which variation was used, and that cannot be automated.

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