This cipher technique considered more secure compared to other substitution algorithms reason being it breaks the message apart into two separate streams and then recombines them. It is a combination of the Polybius square with the transposition and uses fractionation to achieve diffusion. This encrypting technique invented by Felin Delastelle. It just only ever used by amateur cryptographers.

**Encrypting Algorithm:**

For this cipher technique algorithm, we use the 25-letter “key-Square” table.

**Example:**

1 2 3 4 5 1 R A N C H 2 O B D E F 3 G I K L M 4 P Q S T U 5 V W X Y Z

Here we merged J with the I because we are using a 5 X 5 square key matrix so we can use only 25 characters out of the 26.

Let us take “RAMSWARUP IS THE STUDENT OF THE NIT CALICUT” as our plain text.

**Step-1:**

Now find each letter of the plain text in the key-square and write the corresponding row number and column in two separate lines. For example, our first letter is the “R” which is present in the first row and first column, so the key cipher text key value for it is “1-1”.

RAMSWARUP IS THE STUDENT OF THE NIT CALICUTROW : 113451144 34 412 4442214 22 412 134 1133144 COL : 125322151 23 454 3453434 15 454 324 4242454

**Step-2:**

Now select a certain amount of size (this is called the period) which indicate how many key values we are going to take. for example in this example take the block size is 5. So divide the values in the block of the period.

ROW:11345 11443 44124 44221 42241 21341 13314 4COL:12532 21512 34543 45343 41545 43244 24245 4

**Step-3:**

Now merge the values of rows and columns. Rows values followed by the columns. Final values after combining the values of rows and columns:

1134512532 1144321512 4412434543 4422145343 4224141545 2134143244 1331424245 44

**Step-4 (Final Step):**

Now select pair values from the final combined values and take corresponding character value from the key-square matrix. (first value indicates the row number and second value indicates the column values).

For example first taken value is 11 which indicates the character “R” and then we took 34 which is representing the character “L”.

CIPHER-TEXT:RLVFIRTIHATASUSTBCXSQECHUOLCITNGQQUT

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