Cryptography is writing is a disguised way using a secret code. Sometime the word ‘cipher’ is used instead of code. It is said that Julius Caesar used a cipher to keep his message secret from enemy eyes. In modern time, ciphers and codes are used by both government and business for important and secret messages.
There are two kinds of cipher. One kind is the substitution of a number , letter, or other symbol for each letter in a message. The other kind is the transposition or rearrangement of the order of the letters in a message. These two types can be used for a message which can be translated by use of a code book held by both sender and the receiver of the message.
Codes and ciphers can be “broken”, or solved, by direct methods of deciphering and decoding. But to do this, the key to a cipher or code book is necessary, which is generally hard to find. A scientific method of reading cryptograms (secret message) has been developed and is called crypto analysis. A person reading cryptograms must first determine in what language the secret message has been written. He must decide whether the message is in cipher or code. Tables of the frequency of the use of letters in a language, and many other things, are necessary in breaking ciphers and codes.
In simple terms – Cryptography is the discipline which embodies the principles, means and methods for the transformation of data in order to hide its information content, present its undetected modification and prevent its unauthorized use.