SSL-protocol and SSL-certificate
The SSL protocol can be used to only secure the connection, but it also enables reliable user authentication.
Both encrypted connection and user authentication are based on asymmetric encryption, where two different keys are used to encrypt and decrypt the message. One of the keys is a secret key and the other is a public one. That is why it is called a public key method. To encrypt the actual communication, a symmetric method is used, the key of which is sent to the other party encrypted with the recipient's public key.
To identify the user, a certificate is needed in addition to the public key. To prove that the public key belongs to a particular person or server, the certificate must be signed electronically by a trusted certificate authority.
When authenticating in to a protected service, the user sends their certificate and a message signed with the secret key to the server. By unpacking this message with a public key found on the certificate, the server ensures that the user also holds the secret key. Similarly, the user can verify the authenticity of the server based on the certificate sent by the server.
In an SSL-protected connection, the browser usually displays an image of a lock or equivalent in the status bar, and the URL begins in https: instead of the normal http.
In addition to a secure connection, search engines like Google favor websites that use https in their search results.