Secure Sockets Layer (SSL) is the most popular standard for securing Internet communications and transactions. Secure web applications use HTTPS (HTTP over SSL). The HTTPS protocol uses certificates to ensure confidential and secure communications between server and clients. In an SSL connection, both the client and the server encrypt data before sending it. Data is decrypted upon receipt.
When a Web browser (client) wants to connect to a secure site, an SSL handshake happens, like this:
The browser sends a message over the network requesting a secure session (typically, by requesting a URL that begins with https instead of http).
The server responds by sending its certificate (including its public key).
The browser verifies that the server's certificate is valid and is signed by a CA whose certificate is in the browser's database (and who is trusted). It also verifies that the CA certificate has not expired.
If the certificate is valid, the browser generates a one time, unique session key and encrypts it with the server's public key. The browser then sends the encrypted session key to the server so that they both have a copy.
The server decrypts the message using its private key and recovers the session key.
After the handshake, the client has verified the identity of the Web site, and only the client and the Web server have a copy of the session key. From this point forward, the client and the server use the session key to encrypt all their communications with each other. Thus, their communications are ensured to be secure.
The newest version of the SSL standard is called Transport Layer Security (TLS). The Enterprise Server supports the SSL 3.0 and the TLS 1.0 encryption protocols.
To use SSL, Enterprise Server must have a certificate for each external interface or IP address that accepts secure connections. The HTTPS service of most web servers will not run unless a certificate has been installed. For instructions on applying SSL to HTTP listeners, see To Configure an HTTP Listener for SSL.
A cipher is a cryptographic algorithm used for encryption or decryption. SSL and TLS protocols support a variety of ciphers used to authenticate the server and client to each other, transmit certificates, and establish session keys.
Some ciphers are stronger and more secure than others. Clients and servers can support different cipher suites. During a secure connection, the client and the server agree to use the strongest cipher that they both have enabled for communication, so it is usually sufficient to enable all ciphers.
Using name-based virtual hosts for a secure application can be problematic. This is a design limitation of the SSL protocol itself. The SSL handshake, where the client browser accepts the server certificate, must occur before the HTTP request is accessed. As a result, the request information containing the virtual host name cannot be determined prior to authentication, and it is therefore not possible to assign multiple certificates to a single IP address.
If all virtual hosts on a single IP address need to authenticate against the same certificate, the addition of multiple virtual hosts probably will not interfere with normal SSL operations on the server. Be aware, however, that most browsers will compare the server's domain name against the domain name listed in the certificate, if any (applicable primarily to official, CA-signed certificates). If the domain names do not match, these browsers display a warning. In general, only address-based virtual hosts are commonly used with SSL in a production environment.