Secure Sockets Layer (SSL), is cryptographic protocol that provide communication security over the Internet.

SSL encrypt the segments of network connections above the Transport Layer, using symmetric cryptography for privacy and a keyed message authentication code for message reliability. Several versions of the protocols are in widespread use in applications such as web browsing, electronic mail, Internet faxing, instant messaging and voice-over-IP (VoIP).

The protocol uses a third party, a Certificate Authority (CA), to identify one end or both end of the transactions. This is in short how it works.

1. A browser requests a secure page (usually https://).
2. The web server sends its public key with its certificate.
3. The browser checks that the certificate was issued by a trusted party (usually a trusted root CA), that the certificate is still valid and that the certificate is related to the site contacted.
4. The browser then uses the public key, to encrypt a random symmetric encryption key and sends it to the server with the encrypted URL required as well as other encrypted http data.
5. The web server decrypts the symmetric encryption key using its private key and uses the symmetric key to decrypt the URL and http data.
6. The web server sends back the requested html document and http data encrypted with the symmetric key.
7. The browser decrypts the http data and html document using the symmetric key and displays the information. Several concepts have to be understood here.