What is X.509 standard and certificate?

X.509 is a standard used for public-key certificates or digital documents. An assigned cryptographic key pair is paired with a user, organization, website, or device.

X.509 certificate is a digital certificate that uses the X.509 Public Key Infrastructure (PKI) standard to verify the ownership of a public key. The certificate can be used for asymmetric or symmetric encryption, which can belong to a user, website, device, or an organization. An X.509 certificate contains information about the certificate’s owner and about the certificate itself. Some of the data includes:

• Version: X.509 version applicable to the certificate, which suggests the information the certificate would include.
• A unique serial number of the certificate
• The algorithm used by the issuer to sign the certificate
• Name of the Issuer (Certificate Authority)
• Validity Period of the certificate
• The name of the owner of the certificate
• Public Key associated with the certificate
• Optional extensions