The SSL Protocol

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HP Open Source Security for OpenVMS Volume 2:...

Overview of SSL

The SSL Handshake

The SSL Protocol

This section provides an overview of SSL technology and its application.

The SSL protocol works cooperatively on top of several other protocols. SSL works at the application level. The underlying mechanism is TCP/IP (Transmission Control Protocol/Internet Protocol), which governs the transport and routing of data over the Internet. Application protocols, such as HTTP (HyperText Transport Protocol), LDAP (Lightweight Directory Access Protocol), and IMAP (Internet Messaging Access Protocol), run on top of TCP/IP. They use TCP/IP to support typical application tasks, such as displaying web pages or running email servers.

SSL addresses three fundamental security concerns about communication over the Internet and other TCP/IP networks:

SSL server authentication -- Allows a user to confirm a server's identity. SSL-enabled client software can use standard techniques of public-key cryptography to check whether a server's certificate and public ID are valid and have been issued by a Certificate Authority (CA) listed in the client's list of trusted CAs. Server authentication is used, for example, when a PC user is sending a credit card number to make a purchase on the web and wants to check the receiving server's identity.

SSL client authentication -- Allows a server to confirm a user's identity. Using the same techniques as those used for server authentication, SSL-enabled server software can check whether a client's certificate and public ID are valid and have been issued by a Certificate Authority (CA) listed in the server's list of trusted CAs. Client authentication is used, for example, when a bank is sending confidential financial information to a customer and wants to check the recipient's identity.

An encrypted SSL connection -- Requires all information sent between a client and a server to be encrypted by the sending software and decrypted by the receiving software, thereby providing a high degree of confidentiality. Confidentiality is important for both parties to any private transaction. In addition, all data sent over an encrypted SSL connection is protected with a mechanism that automatically detects whether data has been altered in transit.

The SSL Handshake