Cipher guides · Substitution

How to Solve the Caesar Shift Cipher

A substitution cipher swaps every letter for another letter and keeps that swap for the whole message. The text still looks like text — same word lengths, same spacing, same doubled letters — it just isn't in English yet.

How to recognise it

Word shapes survive. If you can see one- and two-letter words, an apostrophe, or the same letter doubled in the middle of a word, you are almost certainly looking at a substitution.

Caesar Shift Every letter has slid 3 places down the alphabet. Slide them back.

The key, letter by letter

A → D
B → E
C → F
D → G
E → H
F → I
G → J
H → K
I → L
J → M
K → N
L → O
M → P
N → Q
O → R
P → S
Q → T
R → U
S → V
T → W
U → X
V → Y
W → Z
X → A
Y → B
Z → C

A worked example

Message

TREASURE MAP

Key

shift 3

Encoded

WUHDVXUH PDS

Every letter has been swapped for another one, and the same swap is used all the way through. Letter shapes stay put — word lengths and spacing are still real clues. This one is Caesar Shift. The key: shift 3. Every letter has slid 3 places down the alphabet. Slide them back. Take the first letter, W, and walk it back 3 places: it lands on T. Do that to every letter and the message reads T R E… The answer was TREASURE MAP.

Working one out from scratch

Start with the short words and the most common letter. In English that letter is usually E, and a lone letter is usually A or I. Two or three correct guesses tend to collapse the rest of the message on their own.

Now try one

There’s a new cipher waiting today

One a day, three guesses, and a streak that breaks the moment you miss one. Today’s is cipher #1.

Today’s cipher All cipher guides