Columnar Transposition: Scrambling Order, Not Letters

Substitution ciphers replace letters. Transposition ciphers keep every letter but change their order. Columnar transposition is the classic example and was used in military field ciphers into the 20th century.

How it works

1. Pick a keyword, e.g. ZEBRA.
2. Write the message in rows under the keyword, one letter per column.
3. Number the columns by the alphabetical order of the keyword letters: A=1, B=2, E=3, R=4, Z=5.
4. Read the columns out in that order.

Why it resists simple attacks

Letter frequencies are unchanged, which tells a codebreaker a transposition was used, but not the order. Longer keywords and doing it twice (double transposition) made it much harder.

How it's broken

Analysts guess the number of columns, then rearrange them to form common letter pairs such as TH, HE and IN. This is called anagramming the columns.

Try your own keyword with the columnar transposition tool on CaesarCipher.org.

Disclosure: written by the CaesarCipher.org team.