Certificate Authorities (CAs)

Certificate Authorities (CAs) are trusted entities that issue digital certificates, which are used to establish a chain of trust on the internet, especially for securing communications over the web. These certificates are a crucial component of the [[SSL-TLS|SSL/TLS]] (Secure Sockets Layer/Transport Layer Security) protocols, which provide secure web browsing and data transmission.

CAs issue digital certificates to entities (such as websites, organizations, or individuals) after verifying their identity. This certificate binds a public key to the entity identified in the certificate, typically through a domain name for [[SSL certificates|SSL/TLS certificates]].

When a user visits a website secured with SSL/TLS, the browser checks the website's SSL certificate. A valid certificate issued by a trusted CA ensures the user that the website is legitimate and not an impostor. CAs are a fundamental part of the Public Key Infrastructure, an arrangement that binds public keys with respective user identities by means of a Certificate Authority (CA).

There is often a hierarchy of trust in the CA world, with root CAs at the top issuing certificates to intermediate CAs, which in turn can issue certificates to end entities (like websites).

CAs offer different levels of validation for issuing certificates:

• Domain Validation (DV): The CA checks the right of the applicant to use a specific domain name. This is the most basic level of validation.
• Organization Validation (OV): The CA checks the right to use a domain name and conducts some vetting of the organization.
• Extended Validation (EV): This is the highest level of validation, where the CA conducts a thorough examination of the organization, including its legal and physical existence.

CAs maintain lists of revoked certificates. A certificate may be revoked if it is discovered that the certificate was issued improperly or the private key has been compromised. By providing verified certificates, CAs enable secure communications over the internet, protecting data from eavesdroppers and attackers.

Web browsers and operating systems maintain a list of trusted CAs. If a certificate is issued by a CA not in this list, the browser may warn the user that the connection is not secure.

CAs operate under specific standards and regulations to ensure they provide a high level of security and trust. They are often audited and must adhere to standards like those set by the WebTrust program or the CA/Browser Forum.

Certificate Authorities play a crucial role in internet security. The trust model provided by CAs underpins secure online transactions, including online shopping, banking, and confidential communications.