140、Suppose you are about to provide your credit card number when ordering merchandise over the World Wide Web.How do you know for sure that the sit you have contacted is the business you think it is? Suppose a brokerage firm receives a request via its Web site to sell a client’s stock.How does it know that the request came from the client rather than an impostor? The Secure Socket layer( ) is a protocol system that uses public-key encryption techniques to resolve such questions.It also allows the messages between the client and server to be encrypted.To communicate via AAL, both a client and a server must register in advance with a third site known as a certification authority.The client then contacts the server using the SSL protocol, which causes both the client and the server to contact the certification authority to confirm the authenticity of each other before further communication.During this authentication process they also obtain the encryption keys needed to encrypt their communication. Most Web browsers support SSL in such a way that its use is transparent to the user.Once a user has registered with a certification authority, SSL is activated merely by contacting a server with a URL beginning with https rather than http as in traditional hypertext protocol communication.(5)、Choose a title for this text.