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X.509

X.509 is a standard that defines the format of public key certificates. The standard is based on ASN.1.
An X.509 certificate consists of a public key and an identity such as a hostname, an organization or an individual. This data is signed by a certificate authority (CA) or is self-signed.
X.509 certificates are used, for example, in SSL/TLS
X.509 can be contrasted to the PGP's web of trust. The former uses a hierarchical approach based on a certificate authority.

See also

Security: credentials
makecert.exe creates X.509 certificates
A typical file extension for Base64 decoded certificates is .cer.
The PowerShell cmdlet new-selfSignedCertificate creates X.509 certificates and private key/public key pairs
RFC 8555 describes a protocol between a CA and an applicant that can be used to automate the process of verification and certificate issuance.
Let's Encrypt (certbot) uses this protocol.

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