The Rail Fence cipher rearranges letters along a zigzag. Start on the top rail, move down to the bottom, then climb back up. Once the message is written, read each rail from left to right, starting at the top.
The path used here
The grid uses A–Z letters only. Spaces and punctuation are removed, and you can see the changes in the prepared input. Decoding restores those prepared letters, without the original spacing or punctuation.
- Choose 2–12 rails.
- Begin on the top rail and move downward. The offset is zero.
- Reverse direction at the top and bottom rails.
- Do not pad short rails with X or another character.
Three rails, zero offset
WEAREDISCOVEREDFLEEATONCE3 rails; start at top; first direction downWECRLTEERDSOEEFEAOCAIVDEN| Rail | Letters read |
|---|---|
| 1 | WECRLTE |
| 2 | ERDSOEEFEAOC |
| 3 | AIVDEN |
How to decode the zigzag
First mark a zigzag with as many positions as there are ciphertext letters. Count the positions on each rail, fill the rails from top to bottom, then follow the zigzag to read the message. Do not split the ciphertext into equal pieces: the rails usually hold different numbers of letters.
The example has 25 letters, divided into rails of 7, 12, and 6. Blank grid cells are simply outside the path. They do not stand for spaces or missing letters.
Try one yourself
Encode MEETME using 3 rails. First write down the rail sequence 1, 2, 3, 2, 1, 2.