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From time immemorial, people have used cryptography to scramble messages to maintain their confidentiality.  At the point of origin, the message is scrambled and at the point of destination, it is descrambled as per a prearranged logic.  This is now an emerging option due to the increase in the volume of trade and commerce done through the internet.  To trade commodities online data security now assumes greater importance.

To understand encryption, let us look at an example.  If you want to send the message: 'Hello world' on the internet, you may encrypt it by replacing each letter by the next letter, so 'h' become 'I'; 'e' becomes 'f' and so on. 

There are four elements to an encryption system:
•   The plain text or the message to be encrypted.  In our example, it is 'Hello world'.
•   The key that is the string or digits.  In our example it is 'l'.
•   The cipher text is the encrypted message.  In our example it is 'Ifmmp Xpsme'
•   Cryptographic algorithm: This is the logic to combine the plain text with the key to generate the 'cipher text'.  It is also used to convert the cipher text to plain text using the key.  In our example, the cryptographic algorithm for encryption is 'replace each letter by the letter that succeeds it by the number represented by the key.  The logic for decryption is the reverse of this procedure

As per this scheme, if the key were '2', the cipher text would have been 'Jgnng Ygtnf'.  There are two common type encryptions in use today.  They are,
•   Secret-key
Public-key encryption

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