We are going to see one of the earliest method used in cryptography to send secret messages. It was used by Julies Caesar and hence named Caesar cipher.
Here, each letter of the message is shifted forward by 3 places in the alphabet. That is, A will become D, B will become E and so on.
For quick reference;
Plain text: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher text: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
So the message
'Welcome to my blog'
encrypted as
'ZHOFRPH WR PB EORJ'
This is technically called mono alphabetic substitution cipher. Here a shift of +3 is used. But we could use a shift of +1 to +25. A person who knows the algorithm (method) can only decipher the code and retrieve the message. Suppose someone wants to break the code and get the message, Is there a way? Yes, there is.
The appearance of letters in English language has certain frequencies as given below.
The letter E has highest frequency followed by other alphabets. In the ciphered text, letters have changed not the frequency. Suppose the frequency of appearance of H is 12 % in the encrypted message, it must stand for E since the frequency of E is 12.5% in the English language. Hence, by estimating the frequency of ciphered letters, one can get back the original message.
There are some additional informations in the language. An intelligent code breaker will use them also.
There are some common pairs of letters: TH, EA, OF, TO, IN, IT, IS, BE, ...
Some common triplets : THE, EST, FOR, AND, HIS, ENT, THA.
Common repeated letters: SS, EE, TT, FF, MM, AND OO.
And lone letters I or A.
These informations are of great value to the cryptographer. But the above method may not work for very short message.The war between encoders and core breakers was always there. But now, the cryptography has evolved and become sophisticated.
All communication channels like bank website, on line stores, whatsapp, messenger uses encryption. It is difficult to crack them even using powerful computer.
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