Rail Fence Cipher

The Rail Fence cipher is a transposition cipher that writes the message in a zigzag pattern across multiple 'rails' (rows), then reads off each rail in order to produce the ciphertext. The number of rails is the key.

Used during the American Civil War for quick field encryption. The simplicity made it popular for tactical communications where speed was more important than strong security. Ancient Greeks used a similar technique called the scytale.

While too weak for serious encryption, rail fence ciphers are used in puzzle games, escape rooms, and as educational tools. Sometimes combined with other ciphers to add a layer of transposition to a substitution cipher.

Very limited key space (only n-1 possible keys for a message of length n). Vulnerable to brute force - an attacker can simply try all possible rail counts. Pattern analysis can reveal the number of rails. Does not hide letter frequencies.