The Secure Sockets Layer (SSL) protocol has become the universal standard on the Web for authenticating sites and for encrypting communications between users and Web servers. Because SSL is built into all major browsers and Web servers, simply installing a digital certificate or Server ID enables SSL capabilities. SSL server authentication allows users to confirm a Web server's identity. SSL-enabled client software, such as a Web browser, can automatically check that a server's certificate and public ID are valid and have been issued by a certificate authority (CA) — such as VeriSign — listed in the client software's list of trusted CAs. SSL server authentication is vital for secure e-commerce transactions.