Definition
A certificate authority (CA) is a trusted entity that issues digital certificates, acting as a digital notary for online identities. These certificates verify the authenticity of websites, software, and individuals, ensuring that the digital information exchanged is legitimate. CAs operate by validating the identity of an applicant before issuing a digital certificate, which contains the applicant's public key and other identifying information. This process is crucial for establishing trust in digital communications, preventing impersonation and man-in-the-middle attacks. For instance, when you visit a secure website, your browser checks the site's SSL certificate, issued by a CA, to confirm its identity. Unlike a registration authority (RA) which verifies identities but does not issue certificates, a CA performs both functions. Certificate authority concepts are fundamental to cybersecurity and appear on exams like CompTIA Security+, CySA+, and CISSP.