Cipher guides · Substitution

How to Solve the A1Z26 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.

A1Z26 Each number is a letter's position in the alphabet.

The key, letter by letter

A → 1
B → 2
C → 3
D → 4
E → 5
F → 6
G → 7
H → 8
I → 9
J → 10
K → 11
L → 12
M → 13
N → 14
O → 15
P → 16
Q → 17
R → 18
S → 19
T → 20
U → 21
V → 22
W → 23
X → 24
Y → 25
Z → 26

A worked example

Message

TREASURE MAP

Key

A=1

Encoded

20-18-5-1-19-21-18-5 13-1-16

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 A1Z26. The key: A=1. Each number is a letter's position in the alphabet. Apply the key to the first three letters and they resolve to 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.

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