An SSL (Secure Sockets Layer) certificate is a digital certificate that provides authentication and encryption for secure communication between a client (such as a web browser) and a server (typically a website). SSL certificates are used to establish a secure and encrypted connection, ensuring that the data transmitted between the client and server remains confidential and protected from unauthorized access or tampering. This is particularly important for websites handling sensitive information, such as online banking, e-commerce, or login pages.
SSL certificates contain the following information:
- The domain name for which the certificate has been issued
- The organization or individual that owns the domain
- The certificate’s public key, used for encryption
- The certificate’s validity period (start and end dates)
- The digital signature of the Certificate Authority (CA) that issued the certificate
When a client (browser) connects to a server (website) with an SSL certificate, the following process occurs:
- The client requests the server’s SSL certificate.
- The server sends its SSL certificate to the client, including its public key.
- The client verifies the certificate’s authenticity by checking the issuing CA’s digital signature and ensuring the certificate has not expired.
- If the certificate is valid, the client generates a unique session key, encrypts it with the server’s public key, and sends it back to the server.
- The server decrypts the session key using its private key and establishes a secure, encrypted connection with the client.
The entire process is known as an SSL/TLS (Transport Layer Security) handshake. SSL has been succeeded by TLS, but the term “SSL” is still commonly used to refer to these digital certificates and the secure connections they enable.