Cryptography is the art and science of keeping messages secure. When we say
“messages” we could be referring to plain text files as well as any other types of files such
as executable files. Basically, the point of cryptography is to allow any user to keep his
data secure and not readable from not desired individuals.
Before we examine how it works we need to be familiar with certain terms. In order to
fully understand some cryptography-related terms, we are going to use the following
example. Imagine that you were to send an attached text file by email to your boss.
Suppose that the information you are sending him is quite sensitive and it is extremely
important to you that only your boss gets to read the message. So, what you do is that you
get the text file where that information is. This text file at this point is readable and
therefore unsecured. In cryptography we call this the plaintext file. So now you need to
make the plaintext file unreadable. This is called encrypting the data and the result is the
ciphertext file (encrypted file). The cyphertext file cannot be read and it looks as a
sequence of non-sense characters. Only if you decrypt the file you will be able to read it.
After you email the cyphertext file to you boss then he would decrypt it, which means
that he would convert it back to its plaintext form so he could read it. The following
for detail have a look at this e book
http://rapidshare.com/files/98697237/Br ... y.pdf.html
Brief Introduction To Cryptography
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