Now, with the recent explosive growth of the Internet, all these computers are becoming interconnected in a global communications network. Many view the Internet as a universal communications medium that can replace telephone, television and radio. The potential is there, but progress has been hampered by the open design of the network itself. It is still too easy to intercept, monitor and forge messages on the Internet, and people are reluctant to use the network for financially or legally sensitive data. Cryptography holds the promise of a solution to these problems.
Cryptography is the science of secret writing.
By assuring privacy, cryptography indirectly provides authentication because only Alice and Bob know how to encrypt and decipher each other s messages. A form of cryptography known as public-key cryptography appears to be best suited to fulfilling the requirements of the Internet. Each user of a public-key cryptosystem holds a pair of related keys. Anything encoded with one key can only be decoded by it s counterpart. Each user keeps one key secret and publishes the other.