Rail Fence Cipher

Write the message in a zigzag over several rows, then read it row by row. The letters stay the same; only their positions change.

Transpositiondemo

Objectives

Encrypt a message across a chosen number of rails.
Compare letter counts before and after transposing.
Explain why unchanged frequencies announce a transposition cipher.

50%

Do not replace letters. Reorder them. Same letters, new positions.

Plaintext

Rails

W . . . V . . . O . . . B . . . T . . . E . . 
. E . A . E . M . L . A . O . T . H . D . A . 
. . H . . . A . . . E . . . R . . . E . . . L

ciphertext: read the rails left to right, top to bottom

WVOBT EEAEM LAOTH DAHAE REL

Letter counts, before and after

plaintext

A:4 B:1 D:1 E:5 H:2 L:2 M:1 O:2 R:1 T:2 V:1 W:1

ciphertext

A:4 B:1 D:1 E:5 H:2 L:2 M:1 O:2 R:1 T:2 V:1 W:1

Identical. A transposition cipher only moves letters, so it cannot change their frequencies. English-looking frequencies on text that reads as nonsense announce a transposition before you have guessed a single key.

step 1/2

CPE 645 / CS 685

Rail Fence Cipher

Vernam Cipher and the One-Time Pad

Columnar Transposition