Skip to main content
▮ CipherChronicle
fr — Français en — English
Sign in

Cipher methods Transposition

Rail Fence (zig-zag)

A zigzag transposition across several rails. The message is written diagonally, then read rail by rail.

Family :
Transposition
Difficulty :
Beginner
Era :
Classical cryptography

Also known as : zigzag cipher · fence cipher

The Rail Fence cipher (or zigzag) is the canonical example of a transposition cipher: no letter is changed, only rearranged following a geometric pattern.

Principle

Write the plaintext diagonally, top-down then bottom-up, across a fixed number of rails (rows). The ciphertext is read by concatenating each rail left to right.

With 3 rails and CIPHERCHRONICLE:

Rail 1 : C . . . E . . . R . . . C . . .
Rail 2 : . I . H . R . H . O . I . L . .
Rail 3 : . . P . . . C . . . N . . . E .

Reading rail by rail: CERC + IHRHOIL + PCNE = CERCIHRHOILPCNE.

The key is simply the number of rails (here 3).

Variants

  • Redefence — same principle but with a starting offset (you don’t have to begin on the first rail).
  • Scytale — ancient variant that uses a cylinder rather than a sheet.
  • Columnar transposition — generalization where column order is permuted by a keyword.
  • Double transposition — Rail Fence applied twice with different rail counts.

Strengths and weaknesses

Strengths

  • Trivial to apply by hand, even for a child.
  • Resists raw frequency analysis — letter distribution stays identical to the plaintext.

Weaknesses

That’s also its tell: if the frequency distribution looks normal but the text reads as gibberish, you’re facing a transposition.

  • Brute force: humanly, rail counts range from 2 to 10. Testing each is instant.
  • Text structure: ciphertext length divided by the number of rails often hints at the correct key (the zigzag should fill rails evenly).

In CipherChronicle

Rail Fence is the gateway to transpositions, stepping out of the substitution world (Caesar, Atbash). Its grids reward players who notice the “natural” distribution and realize no letter was swapped.

Grid

C
E
R
C
I
H
R
H
O
I
L
P
C
N
E
Q
R
S
T
U
V
W
X
Y
Z
Key3 rails
  1. 1

    Ciphertext

    The letters are all there, but in seemingly random order — no substitution.

  2. 2

    Transposition detected

    The frequency distribution matches the plaintext — no letter was replaced, only shuffled.

  3. 3

    Hypothesis: 3 rails

    The message was written zigzag on 3 lines, then read line by line.

  4. 4

    Reconstructing the zigzag

    Redraw the rails and replace each letter on its diagonal position.

  5. 5

    Message revealed

    The original order is restored by reading the zigzag left to right.
Encrypt your own text Decrypt some text