SSL (Secure Sockets Layer) Protocol

When you log in to the NIOS appliance, your computer ma kes an HTTPS (Hypertext Transfer Protocol over Secure Sockets Layer protocol) connection to the NIOS appliance. HTTPS is the secure version of HTTP, the client-server protocol used to send and receive communications throughout the Web. HTTPS uses SSL (Secure Sockets Layer) to secure the connection between a client and server. SSL provides server authentication and encryption. The NIOS appliance supports SSL versions 2 and 3.
When a client first connects to a server, it starts a series of message exchanges, called the SSL handshake. During this exchange, the server authenticates itself to the client by sending its server certificate. A certificate is an electronic form that verifies the identity and public key of the subject of the certificate. (In SSL, the subject of the certificate is the server). Certificates are typically issued and digitally signed by a trusted third party, the Certificate Authority (CA). A certificate contains the following information: the dates it is valid, the issuing CA, the server name, and the public key of the server.
A server generates two distinct but related keys: a public key and a private key. During the SSL handshake, the server sends its public key to the client. Once the client validates the certificate, it encrypts a random value with the public key and sends it to the server. The server decrypts the random value with its private key.
The server and the client use the random value to generate the master secret, which they in turn use to generate symmetric keys. The client and server end the handshake when they exchange messages indicating that they are using the symmetric keys to encrypt further communications.

Figure 1.2 SSL Handshake