Certificates

In short: A certificate is a digital ID. It links a public key to an identity (website, person, company) and is signed by a trusted body.

In more detail: The word stands for several kinds. The basic idea is always the same: a certificate authority (CA) confirms that the key really belongs to the name.

In Depth

• TLS certificate: for websites and the connection via HTTPS, see certificates in web development.
• Email certificate (S/MIME): for signing and encrypting email.
• Code signing: proves who a program comes from and that it is unchanged.
• Client certificate: login for people or devices without a password.
• Qualification certificates: in everyday life also documents such as school or chamber-of-commerce certificates. Same word for “proof”, but technically something entirely different.

How the check works

The device contains a list of trusted root certificates. A certificate is valid if its chain leads there, it is not expired or revoked, and the name matches. The mathematics behind it is asymmetric encryption.

See also: certificate, TLS