Final answer:
The answer is option A. Certificates validate the identity of the source by binding a public key to the source's identity information and are an integral part of Public Key Infrastructure (PKI) for web security.
Step-by-step explanation:
Certificates are used to verify the identity of the source. They bind a public key with information about the source, which can include the source's name, a serial number, expiration dates, and the digital signature of the certificate-issuing authority, establishing a chain of trust.
The most common use of a certificate is in the context of Secure Sockets Layer (SSL) for web security. When you visit a website with SSL, the site presents a certificate to your browser. Your browser then checks that the certificate is valid, is signed by a trusted certificate authority, and that it is related to the site contacted.
The process of binding this information in the certificate is governed by protocols such as those specified by the Public Key Infrastructure (PKI). This infrastructure is essential for creating, managing, distributing, using, storing, and revoking digital certificates and managing public-key encryption.