How to Solve the Columnar Transposition Cipher

A transposition cipher doesn't change any letters at all. Every letter of the answer is already in front of you; they have simply been written down in the wrong order.

How to recognise it

Count the letters. If the frequencies look like ordinary English — plenty of E, T, A, O — but nothing reads, the message has been reordered rather than substituted.

Columnar Transposition Written in rows under the keyword, then read out one column at a time — columns taken in alphabetical order of their letter.

A worked example

Every letter of the answer is already in front of you — they are simply in the wrong order. Counting the letters is the first useful thing you can do. This one is Columnar Transposition. The key: keyword ANVIL. Written in rows under the keyword, then read out one column at a time — columns taken in alphabetical order of their letter. Rebuild the grid, read it back in the original order, and the first letters come out T R E. The answer was TREASURE MAP.

Working one out from scratch

Find the shape the writer used: how many rails, how many columns, which route. The letter count is your best lever, because it tells you which rectangles the message could have been written into.