Trifid cipher is a combination of a substitution cipher and a transposition cipher.
It was developed in 1901 by the French cryptologist Felix Delastelle as a development of the bifid cipher. Delastelle was a French who invented several ciphers, including two, three and four square ciphers.
The trifid cipher consists of a code table with three 3x3 code squares. The sum of the fields is 3x3x3, i.e. 27 characters. The Latin alphabet contains 26 letters, therefore the dot (.) character is used to complete.
Square 1


Square 2


Square 3


1 
2 
3



1 
2 
3



1 
2 
3

1

A 
B 
C 

1

D 
. 
E 

1

F 
G 
H

2

I 
J 
K 

2

L 
M 
N 

2

O 
P 
Q

3

R 
S 
T 

3

U 
V 
W 

3

X 
Y 
Z

For example, we want to encode the word CALCOOLATOR . We choose the coding method (order), e.g. square  row  column. We now look for each letter in the table and assign it the square number, row number and column number in the order we chose.
letter: C A L C O O L A T O R
square: 1 1 2 1 3 3 2 1 1 3 1
row: 1 1 2 1 2 2 2 1 3 2 3
column: 3 1 1 3 1 1 1 1 3 1 1
We arrange the numbers in three by reading in lines. Then, in the table, we look for the letters that our threedigit groups will indicate in the previously established order  first the square, then the row, then the column.
groups: 112 133 211 311 121 222 132 331 131 111 311
square: 1 1 2 3 1 2 1 3 1 1 3
row: 1 3 1 1 2 2 3 3 3 1 1
column: 2 3 1 1 1 2 2 1 1 1 1
letter: B T D F I M S X R A F
So the scrambled word CALCOOLATOR would be BTDFIMSXRAF.
The second step of encryption removes the relationship between the groups of numbers and the corresponding letters, which makes cryptanalysis very difficult. Thanks to the three tables describing the position of the letters, this effect was much stronger than in the bifit cipher. Despite the apparent simplicity, both of these ciphers, when they were created, were very resistant to breaking.
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