Letter Frequency Analysis

Paste any English text and count every letter. This pattern of counts is what a simple substitution cipher cannot hide.

CryptanalysisFrequency analysisdemo

Objectives

Count the letter distribution of a text you choose.
Compare that distribution against the English reference table.
Explain why a short sample ranks E first but does not fix the order after it.

33%

Default text: UAH news, 25 August 2026.

Any English text. Paste your own.

Nothing leaves the browser. Spaces, digits and punctuation are dropped before counting.

letters counted

444

Every attack in this module starts here. A substitution cipher renames the letters and leaves the counts alone, so the shape you are about to see is the shape that survives encryption.

Every letter, counted

letter	count	this text	English
A	38	8.6%	8.17%
B	4	0.9%	1.49%
C	12	2.7%	2.78%
D	14	3.2%	4.25%
E	55	12.4%	12.70%
F	7	1.6%	2.23%
G	10	2.3%	2.02%
H	13	2.9%	6.09%
I	29	6.5%	6.97%
J	1	0.2%	0.15%
K	1	0.2%	0.77%
L	30	6.8%	4.03%
M	15	3.4%	2.41%
N	39	8.8%	6.75%
O	25	5.6%	7.51%
P	5	1.1%	1.93%
Q	0	0.0%	0.10%
R	36	8.1%	5.99%
S	28	6.3%	6.33%
T	37	8.3%	9.06%
U	22	5.0%	2.76%
V	4	0.9%	0.98%
W	10	2.3%	2.36%
X	2	0.5%	0.15%
Y	7	1.6%	1.97%
Z	0	0.0%	0.07%

Q, Z do not appear at all in this text. English has 26 letters and uses about 20 of them for almost everything.

most common in this text

E N A T R L

most common in English

E T A O I N

E comes first in any English text long enough to count. The order after E is a different matter. On 444 letters the topic words push their own letters up: a page about enrollment is full of E, N, L and U whether English is or not. Give the attacker a few hundred more letters and the ranking settles onto the reference column. That is exactly why the score card asks for “about 100 letters” or “about 300 letters” rather than “one ciphertext”.

step 1/3

CPE 645 / CS 685

Letter Frequency Analysis

Where Each One Breaks

Breaking Caesar