Rail Fence Cipher

Module 01 / Lesson 07

Video Tutorial

What is a Rail Fence Cipher?

Rail Fence cipher is a simple transposition cipher that writes the message in a normal pattern on a number of "rails" (horizontal lines), then reads off each rail to create the ciphertext.

Key Components:

Number of rails (key)
Message text
Normal pattern
Reading direction

Key Rules:

Write text down
Write text vertical
Read text horizontally
Spaces are usually removed

Example with 3 Rails (Message: "CIPHERBOY")
                            Read text horizontally ⭢

                            ⭣
⭣
⭣

                            Write message down
                        
                            C   H   B

                            I   E   O

                            P   R   Y
                        
                        Result: "CIPHERBOY" → "CHBIEOPRY"

Python Implementation

def rail_fence_vertical(text, rails):
    text = text.replace(" ", "").upper()
    # Create empty rails
    fence = [[] for _ in range(rails)]
    
    # Write the message down (vertical pattern)
    for i, char in enumerate(text):
        fence[i % rails].append(char)
    
    # Read text horizontally (combine rails)
    ciphertext = "".join(["".join(rail) for rail in fence])
    return ciphertext

# Example
msg = "CIPHERBOY"
print(rail_fence_vertical(msg, 3)) # Output: CHBIEOPRY

← Previous Lesson Back to Module Next Lesson →