#### Caesar Cipher

What-How

Hello, Welcome again.

In this post, we'll look at one of the earliest and simplest technique of encryption called 'Caesar Cipher'.

'Caesar' refers to the 'Julius Caesar', the famous Roman general, statesman and author around 100 BC; and 'Cipher' just means the 'technique'. It's believed that he used this technique for secret communication among his trusted social circle. Now what is this technique? Let's see.

For any message that you have, all the english letters are 'shifted' by a certain number to make the ciphertext from the plaintext message. Example:

Suppose the message/plaintext is: "AMAZON".
Then, for each letter in this text, we 'shift' it by certain number.

Let that 'shift-number' (or 'key' in this case) be 2.
Then, 'A' becomes: 'C', 'M' becomes 'O',
and 'Z' becomes 'B'.
(we wrap around after 'Z', such that 'Z' + 1 = 'A' and 'Z' + 2 = 'B')

The 'encrypted' message becomes "COCBQP" from "AMAZON".

To 'decrypt' this ciphertext, we just 'shift-back' each letter by '2'(which was the 'key' in this case), and get the original plaintext message back.

Note that Numbers, spaces and special characters are left unchanged.
And also each letter can only be shifted to 25 at maximum, because for any english alphabet, there are only 25 other alphabets left. (Just try that: 'A' shifted to 25 becomes 'Z' , but 'A' shifted to 26 becomes 'A' again, so that's of no use)
That's why, in this technique, the Key can only be a number between 1 to 25.

So, this is it. This is Caesar Cipher.

Next

This technique was very popular for centuries, but when, with passage of time, the seriousness in maintaing secrecy of message increased; and this technique's limitations started to scream of its incapability to be much 'secure'; new techniques were invented.
Also, many attacks were invented.

One of the easiest attack with which someone can 'crack' a ciphertext message encrypted using Ceaser Cipher, is 'Brute Force Attack'.
And that's what we will see next.
Bye till then.
:-)

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