🪜 Rail Fence Cipher
Write the message in a zigzag across several rails, then read each rail in turn, the rail fence transposition cipher, with 2-10 rails.
Transformed in your browser, nothing you type is uploaded.
How the rail fence cipher works
Unlike substitution ciphers (which replace letters), the rail fence is a transposition cipher. It keeps the letters but scrambles their order. You write the message diagonally down and up across a set number of "rails", then read off each rail left to right to form the ciphertext. Decoding reverses the zigzag. The number of rails is the key; this tool lets you set 2 to 10.
Because it only rearranges letters, the ciphertext contains exactly the same letters as the plaintext, which is a giveaway, and with so few possible rail counts it's easily brute-forced. It's a classic teaching example of transposition and a common puzzle cipher, not a secure method. Spaces and punctuation are shuffled along with the letters, so results are cleanest on continuous text.
Frequently asked questions
What is a transposition cipher?
One that rearranges the order of the letters rather than replacing them (as a substitution cipher does). The rail fence is a classic example, same letters, scrambled positions.
How does the rail fence pattern work?
You write letters diagonally down then up across the rails, forming a zigzag, then read each rail's letters in order. With 3 rails, "HELLO" is written on a zigzag and read row by row to produce the cipher.
What is the key?
The number of rails. More rails scramble the text more, but there are only a handful of sensible values, which is why the cipher is easy to crack by trying each.
Is the rail fence cipher secure?
No. It preserves the exact letters and has very few keys, so it's quickly broken. It's valued for teaching transposition and for puzzles, not for security.
Does it run locally?
Yes, the zigzag arithmetic is done in your browser; nothing is uploaded.