Secure Sockets Layer is an Internet security protocol utilized by both Web browsers and servers. SSL works by verifying that a particular website or remote server has a valid security certificate and that the certificate has a relationship with the remote destination.
SSL connections, which use the HTTPS protocol when serving secure Web pages, can be distinguished from insecure connections which use the standard HTTP protocol.
The original implementation of the SSL protocol was developed by the Netscape team in the early 1990s. Version 1.0 of SSL never saw a public release due to major security issues in the protocol at the time. SSL version 2.0 was released publicly in 1995 and was followed by a completely rewritten version 3.0 the following year because of numerous outstanding security flaws.
The successor to SSL, Transport Layer Security, was first introduced in 1999 and is still under active development as of 2014. While the differences between SSL and TLS are fairly minor, the two protocols are not interoperable. Should the same protocol not be supported by the two communicating parties, they must negotiate a common protocol to successfully communicate.
Several implementations of SSL and TLS are used in many different services that utilize the Internet, including Web browsing, email, Internet faxing, instant messaging and voice-over-IP (VoIP).