Rail Fence Cipher

The Rail Fence Cipher is a type of transposition cipher where the plaintext is written diagonally in a zigzag pattern across multiple "rails" (rows), then read off line by line.

Step 1: Understand the Concept

In the Rail Fence Cipher, the plaintext is arranged in a zigzag pattern across a certain number of rows (rails). The number of rails is a key in the cipher. After writing the text in this pattern, the ciphertext is obtained by reading the characters row by row.

Step 2: Choose the Number of Rails

Decide on the number of rails (rows) you want to use. For this example, we'll use 3 rails.

Step 3: Write the Plaintext in a Zigzag Pattern

Let's take the plaintext message: WE ARE DISCOVERED RUN

Write it in a zigzag pattern across the chosen number of rails (3 in this case):

W . . . R . . . I . . . V . . . D . . . N
. E . A . E . D . S . O . E . E . . . U .
. . . . . . . . . . C . . . R . . . R . .

Step 4: Read Off the Ciphertext Row by Row

Read each row from top to bottom to obtain the ciphertext:

1. First row: W R I V D N

2. Second row: E A E D S O E E U

3. Third row: C R R

Combine these rows to get the final ciphertext: WRIVDN EAEDSOEEU CRR .

Step 5: Decryption Process

To decrypt the ciphertext, you would reverse the process:

1. Determine the number of characters per row based on the total length of the ciphertext and the number of rails.

2. Write the ciphertext back into the zigzag pattern, filling in each row with the appropriate number of characters.

3. Read off the plaintext by reading diagonally through the zigzag pattern.

Example Decryption

Given the ciphertext WREED EAE DS OE EADICRN and knowing the number of rails (3):

W . . . R . . . I . . . V . . . D . . . N
. E . A . E . D . S . O . E . E . . . U .
. . . . . . . . . . C . . . R . . . R . .

Read the zigzag pattern to get the original message: WE ARE DISCOVERED RUN.

This is the Rail Fence Cipher! You can experiment with different numbers of rails to see how it affects the ciphertext.

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