Classical Cryptography

Vigenere Cipher Cryptanalysis Interactive Demo


STEP 1. INPUT PLAINTEXT AND CIPHERTEXT

The step shows letter frequencies for both plaintext and ciphertext. It also calculates the index of coincidence for the ciphertext and the estimated keyword length given by the Friedman test.

Ciphertext



RESULT OF STEP 1.

Table of Ciphertext letter frequencies.

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

The Index of Coincidence
The estimated Keyword Length

STEP 2. ENTER KEYWORD SIZE

This step examines all cosets for keyword sizes 1,2,..,n. A statistic graph will be generated indicating the average of the incidence of coincidence for each cosets.

Keyword Size





STEP 3. ENTER KEYWORD LENGTH

This step first determines the frequency of occurrence for each letter in the text. It then generates a statistic graph indicating the 26 dot products of the shifted frequency ratio vectors with the frequency vector for English.

Keyword Length