Symmetric key cryptography
Symmetric key cryptography started thousand years ago, when people needed to exchange secrets (for example in a war ). We still mainly uses symmetric key cryptography in our network security. However, today ciphers are much more complex. Let us first discuss traditional algorithms, which were character oriented. Then we discuss modern one which are nit oriented. Traditional ciphers : We briefly introduce some traditional ciphers, which are character oriented. Although these are now obsolete, the goal is to show how modern cipher evolved from them. We can divide traditional symmetric key ciphers in to two broad categories namely -- substitution ciphers and traditional ciphers, as shown in the following figure. Substitution ciphers : A substitution cipher substitute one symbol with another. If the symbol in the plain text are alphabetic character, we replace one character by another. For example, we can replace character 'a' with character 'd' , and characte...