Bob connects to a company web site. His browser indicates that the digital certificate of the web site is valid. This application of encryption is an example of

Public key infrastructure (PKI)

Explanation:

The public key infrastructure is a technology for authenticating users and devices so as to securely exchange data or information over the internet.

With the aid of PKI, two or more communicating device can maintain additional security such as authentication, confidentiality, access Control etc.