Concepts in Data Encryption:
The cipher is a form of mono-alphabetic substitution, but relies on digraphs rather than single letters, and it is simple to master. The Playfair cipher is believed to be the first digraphic system. We start with a keyword and then place the remaining letters in underneath, for instance using "cryptogram" as a keyword we will then get the following.
c r y p t o g a m
b d e f h i
k l n
(the R appears twice in cryptogram, and is skipped the second time, the i and the j share the same location)
The box is then read by columns.
c b q r d s y e u p f v t h w o ij x g k z a l m n
The new string of 26 letters is then transposed on a 5x5 grid, with the i and the j sharing the same location.
c b q r d s y e u p f v t h w o i x g k z a l m n
Now, forget all that stuff we just did, another method, which we are going to use, is to place the keyword as the first series of letters in a 5x5 grid, and fill the remaining letters in.
c r y p t
Using this system, the message to be encrypted is broken up into groups of two letters, a sample message: cows cannot encrypt would be encrypted by co ws ca nn ot en cr yp tz. The z is thrown in because it would easily be recognized as a junk letter after decryption. Now that you have broken up the message, you must take each message pair, and find the letters on the chart, take the row of the first letter, and the column of the second letter, and take the intersecting letter. Next, take the row of the second, the column of the first, and get that intersecting letter. Done, that is how to encrypt a pair, now let's encrypt our message with the chart.
plain text co ws ca nn ot en cr yp tz cipher text co zn yo nn bc fl rc py tz
The main advantage of this system is that it robs a cryptanalyst of it main weapon, as
they are no longer able to look for recurring encoding, as in an e can be
encrypted as a different letter each time. This method is relatively secure, and a large
amount of sample cipher text is required in order to run a
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