What a certificate authority is
A certificate authority, or CA, is a trusted entity that issues digital certificates. A digital certificate confirms that a particular public key belongs to the person, organization, or website named in the certificate. By signing these certificates, the certificate authority acts as a trusted third party that both the owner of the certificate and the party relying on it can trust. This role is central to how secure communication on the internet works.
The trust problem it solves
When your browser connects to a website, it needs a way to be sure the site really is who it claims to be, and not an impostor. The challenge is establishing that trust between two parties that have never met. A certificate authority solves this by vouching for the website's identity: because your browser already trusts the CA, and the CA has signed the website's certificate, your browser can extend that trust to the site. The CA is the common point of trust that makes the system work.
How certificates are issued
To obtain a certificate, a website operator applies to a certificate authority and must demonstrate control over the domain or identity being certified. Once the CA is satisfied, it issues a certificate that binds the website's public key to its identity and signs it with the CA's own key. Browsers and operating systems ship with a built-in list of trusted certificate authorities, so any certificate signed by one of them is automatically recognized as trustworthy.
The chain of trust
Certificate authorities are organized into a chain of trust. At the top are root certificates, which are highly protected and trusted by default. Roots sign intermediate certificates, which in turn sign the certificates issued to websites. When your browser checks a site's certificate, it follows this chain back up to a trusted root. If every link is valid and the chain leads to a root the browser trusts, the certificate is accepted; if any link is broken, it is rejected.
When trust breaks down
Because so much depends on certificate authorities, a compromised or careless CA is a serious problem. If a CA mistakenly or maliciously issues a certificate to the wrong party, that party could impersonate a legitimate website. For this reason, certificate authorities are held to strict standards, and browsers can remove trust in a CA that misbehaves. Mechanisms also exist to revoke certificates that should no longer be trusted, such as when a private key is stolen.
Why it matters
Certificate authorities are a foundation of trust on the modern web, making secure, authenticated connections possible between parties that have never met. Understanding what a certificate authority is - a trusted issuer that vouches for digital certificates - clarifies how your browser decides which sites to trust. For anyone interested in online security, the certificate authority is a key concept behind the everyday padlock icon.
Related on Skillo
See also: What is HTTPS and SSL certificates?, What is encryption? End-to-end encryption explained.
Sources
Published date reflects the original event date (2023-02-07). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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