Editing Polybius square (section)

== Encryption principle ==
There are several encryption methods using the Polybius square. Three of them are described below. 
{| class="wikitable"
|-
! 
! 1 !! 2 !! 3 !! 4 !! 5
|-
! 1
| A || B || C || D || E
|-
! 2
| F || G || H || I/J ||K
|-
! 3
| L || M || N || O || P
|-
! 4
| Q || R || S || T || U
|-
! 5
| V || W || X || Y || Z
|}

=== Method 1 ===
Let's encrypt the word "SOMETEXT" with a [[Caesar cipher]] using a shift equal to the side of our square (5). To do it, locate the letter of the text and insert the one immediately below it in the same column for the ciphertext. If the letter is in the bottom row, take the one from the top of the same column.
{| class="wikitable"
|+
|-
!Letter of the text
|s
|o
|m
|e
|t
|e
|x
|t
|-
!Cipher text letter
|x
|t
|r
|k
|y
|k
|c
|y
|}

Thus, after encryption, we get "xtrkykcy".

=== Method 2 ===
A more complicated method involves a [[Bifid cipher]] without a key (or, in other words, with a key of plain alphabet):
{| class="wikitable"
|-
! 
! 1 !! 2 !! 3 !! 4 !! 5
|-
! 1
| A || B || C || D || E
|-
! 2
| F || G || H || I/J ||K
|-
! 3
| L || M || N || O || P
|-
! 4
| Q || R || S || T || U
|-
! 5
| V || W || X || Y || Z
|}
The message is transformed into coordinates on the Polybius square, and the coordinates are recorded vertically:
{| class="wikitable"
|+
!Letter
|s
|o
|m
|e
|t
|e
|x
|t
|-
!Horizontal coordinate
|3
|4
|2
|5
|4
|5
|3
|4
|-
!Vertical coordinate
|4
|3
|3
|1
|4
|1
|5
|4
|}


Then the coordinates are read row by row:
 34  25  45  34  43  31  41  54  
Next, the coordinates are converted into letters using the same square:
{| class="wikitable"
|+
!Horizontal coordinate
|3
|2
|4
|3
|4
|3
|4
|5
|-
!Vertical coordinate
|4
|5
|5
|4
|3
|1
|1
|4
|-
!Letter
|s
|w
|y
|s
|o
|c
|d
|u
|}
Thus, after encryption, we get "swysocdu".

=== Method 3 ===
{| class="wikitable"
|-
! 
! 1 !! 2 !! 3 !! 4 !! 5
|-
! 1
| A || B || C || D || E
|-
! 2
| F || G || H || I/J ||K
|-
! 3
| L || M || N || O || P
|-
! 4
| Q || R || S || T || U
|-
! 5
| V || W || X || Y || Z
|}
An advanced variation, which involves the following: the obtained primary ciphertext (result From Method 2) is encrypted again. In this case, it is written out without being split into pairs.

 3425453443314154

The resulting sequence of digits is cyclically shifted to the left by one step (an odd number of steps [move 3 to the end]):

 4254534433141543

This sequence is again divided into groups of two:

 42 54 53 44 33 14 15 43

And is replaced with the final ciphertext according to the table:
{| class="wikitable"
|+
!Horizontal coordinate
|4
|5
|5
|4
|3
|1
|1
|4
|-
!Vertical coordinate
|2
|4
|3
|4
|3
|4
|5
|3
|-
!Letter
|i
|u
|p
|t
|n
|q
|v
|o
|}

Thus, after encryption, we get "iuptnqvo".