Secure Sockets Layer (SSL) is a protocol for establishing secure links between networked computers. It allows client and server applications to communicate across a network in a way that is designed to prevent eavesdropping, tampering, and message forgery.

SSL uses a combination of public key and symmetric key encryption to secure the transmission of data. The client and server exchange public keys to establish an SSL connection. The server’s public key is used to encrypt the message, and the client’s private key is used to decrypt it. This ensures that the message can only be read by the intended recipient.

SSL is commonly used to secure Internet communications, such as when a web browser connects to a web server using the HTTPS protocol. It is also used in other applications, such as email, file transfer, and virtual private networks (VPNs).

In order for an SSL connection to be established, the client and server must both have a valid SSL certificate. SSL certificates are issued by certificate authorities (CAs), which are trusted third parties that verify the identity of the parties involved in the SSL connection. This helps to ensure that the client is communicating with the server it thinks it is, and not with an impostor.