Secure Sockets Layer (SSL) is the technology used in most Web-based applications. SSL version 2.0 supports strong authentication of the web server, but the authentication of the client side only comes with version 3.0. SSL v4 is not a defined standard.
Source: TIPTON, Harold F. & KRAUSE, Micki, Information Security Management Handbook, 4th edition (volume 1), 2000, CRC Press, Chapter 3, Secured Connections to External Networks (page 54).