Security and privacy is a concern for everyone who uses the Internet, and the ability to provide secure transactions over the Internet has become one of the key requirements for many business applications. The SocketTools ActiveX Edition has the ability to establish secure connections with servers. Although most of the technical issues such as data encryption are handled internally by the control, a general understanding of the standard security protocols is useful when designing your own applications.
When you establish a connection to a server over the Internet (for example, a web server), the data that you exchange is typically routed over dozens of computer systems until it reaches its destination. Any one of these systems may monitor and log the data that it forwards, and there is no way for either the sender or receiver of that data to know if this has been done. Exchanging information over the Internet could be likened to talking with someone in a public restaurant. Anyone can choose to listen to what you're saying, and unless they introduce themselves, you have no idea who they are or if they've even heard what you said.
To ensure that private information can be securely exchanged over the Internet, two basic requirements must be met: there must be a way to send that information so that only the sender and the receiver can understand what is being exchanged, and there must be a way for them to determine that they each are in fact who they claim to be. The solution to the first problem is to use encryption, where a key is used to encrypt and decrypt the data using a mathematical formula. The second problem is addressed by using digital certificates. These certificates are issued by a certificate authority (CA), which is a trusted third-party organization who verifies the individual or company which is issued a certificate are who they claim to be. These two concepts, encryption and digital certificates, are combined to provide the means to send and receive secure information over the Internet.
The Secure Sockets Layer (SSL) protocol was originally developed by Netscape as a way to exchange information securely over the Internet, and is no longer widely used. Improvements to SSL have resulted in the Transport Layer Security (TLS) protocol, and it has become the the standard for secure communications over the Internet. Both of these protocols are designed to allow a private exchange of encrypted data between the sender and receiver, making it unreadable by an intermediate system. Using the restaurant analogy, it would be as if two people were speaking in a language that only they could understand. Although someone sitting at the next table could listen in on the conversation, they wouldn't have any idea what was actually being said.
A secure connection, for example between a web browser and a server, begins with what is called the handshake phase where the client and server identify themselves. When the client first connects with the server it sends a block of data to the server and the server responds with its digital certificate, along with its public key and information about what type of encryption it would like to use. Next, the client generates a master key and sends this key to the server, which authenticates it. Once the client and server have completed this exchange, keys are generated which are used to encrypt and decrypt the data that is exchanged. With the handshake completed, a secure connection between the client and server is established. SocketTools handles the handshake phase of the secure connection automatically and does not require any additional programming. If a secure connection cannot be established, an error is returned and the network connection is closed.
After the handshake phase has completed, the client may choose to examine the digital certificate that has been returned by the server. The information contained in the certificate includes the date that it was issued, the date that it expires, information about the organization who issued the certificate (called the issuer) and to whom the certificate was issued (called the subject of the certificate). The client may also validate the status of the certificate, determining if it was issued by a trusted certificate authority and was returned by the same company or individual it was issued to. There may be certain cases where the client determines that there's a problem with the certificate (for example, if the certificate's common name does not match the domain name of the server), but chooses to continue communicating with the server. Note that the connection with the server will still be secure in this case. In other cases, for example if the certificate has expired, the client may choose to terminate the connection and warn the user.
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