Elementary Cyptography

Consider the steps involved in sending messages from a sender, S, to a recipient, R.–If S entrusts the message to T, who then delivers it to R, T then becomes the transmission medium.–If an outsider, O, wants to access the message (to read, change, or even destroy it), we call O an interceptor or intruder.

Any time after S transmits it via T, the message is vulnerable to exploitation,

O might try to access the message in any of the following ways:

–Block it, by preventing its reaching R, thereby affecting the availability of the message.

–Intercept it, by reading or listening to the message, thereby affecting the confidentiality of the message.

–Modify it, by seizing the message and changing it in some way, affecting the message's integrity.

–Fabricate  the authentic-looking message, arranging for it to be delivered as if it came from S, thereby also affecting the integrity of the message.

As you can see, a message's vulnerability reflects four possible security failures:

–Interception, interruption, modification, and fabrication.

-Encryption is a technique that can address all these problems.

–Encryption, probably the most fundamental building block of secure computing is a means of maintaining secure data in an insecure environment.

Can be used in protecting programs, databases, networks, and electronic communications

Terminology:

–Encryption is the process of encoding a message so that its meaning is not obvious;

–Decryption is the reverse process, transforming an encrypted message back into its normal, original form.

–Alternatively, the terms encode and decode or encipher and decipher are used instead of encrypting and decrypt.

–A system for encryption and decryption is called a cryptosystem.