THE LIBRARY · FIELD GUIDES

The Cipher Library

How the classical ciphers work, and how to read them by hand.

A cipher is a system for hiding a message in plain sight. Not a code, which swaps whole words for other words, but a rule applied to every letter, the same way, every time. Learn the rule and the message opens.

Almost every cipher on this page belongs to one of two families. A substitution cipher replaces each letter with something else: another letter, a number, a symbol, a fragment of a grid. The letters change, their order does not. A transposition cipher does the opposite. It keeps every letter and scrambles where they sit. Nothing is replaced, everything is moved.

That distinction is the first thing a solver establishes, because it decides the method. Count the symbols. If one dominates the way E dominates English, you are looking at substitution. If the letter frequencies look like ordinary English but the words are nonsense, every letter is present and merely out of order. The American Cryptogram Association has been publishing puzzles built on both families since 1929, and the two-family split still holds.

SUBSTITUTION CIPHERS

Every letter is swapped for another letter. The order of the message never changes, only its clothing.

FIELD GUIDE · SUBSTITUTION CIPHERS

The Alphabet Backwards, and the Cipher Hidden In It

Say it once and it is a party trick. Write it under the alphabet and it becomes a cipher that hid the name of Babylon for twenty-five centuries.

6 MIN READ ATBASH

NUMBER CIPHERS

Letters become numbers. The message stops looking like language, which is most of the disguise.

FIELD GUIDE · NUMBER CIPHERS

A1Z26 Cipher: Letters to Numbers and Back

Every letter has an address: its place in the alphabet. The A1Z26 cipher is nothing more than that arithmetic, and that is exactly why it is the first code most people ever break.

5 MIN READ A1Z26

SYMBOL CIPHERS

Letters become marks: shapes, pockets of a grid, invented glyphs. A substitution cipher wearing a costume.

FIELD GUIDE · SYMBOL CIPHERS

Pigpen Cipher: Decode the Freemason's Cipher

Two grids, two crosses, and an alphabet hidden in the walls. The pigpen cipher has guarded Masonic ledgers and a New York gravestone for two centuries, and it takes ten minutes to learn.

4 MIN READ SUBSTITUTION

WHERE TO GO NEXT

Last updated September 9, 2026