The most common form of cryptographic exchange is probably between a web server and a web browser. The Internet and the World Wide Web would be nothing without a way to safeguard personal information like passwords and credit card numbers. Web browsers and web servers use Public-key cryptography to establish initial trust then safely exchange a symmetric key for the duration of the session. The asymmetric cryptography uses key pairs. One is private and the others is public. The keys are prime numbers of sufficient key length to make it impractical to take the public key and try to guess the private key. It is therefore consider safe. Unfortunately it is too computational intense to use for every piece data the web browser and server exchange. The symmetric key is used for speed.