X.509 Certificate

What Does X.509 Certificate Mean?

An X.509 certificate is any certificate under the X.509 specification standard for public key infrastructure and Privilege Management Infrastructure (PMI) proposed by the International Telegraph Union Telecommunication Standardization Sector (ITU-T) in order to standardize formats for:

  • Attribute certificates
  • Public key certificates
  • Certificate revocation lists
  • Certification validation algorithms

These certificates are used for identity validation and for transmission of encrypted data that only the owner (person, organization or software) of a specific certificate is able to decrypt and read.

Techopedia Explains X.509 Certificate

X.509 certificates act as secure identifiers, digital passports which contain information about the owner. The certificate is tied to a public key value which is associated with the identity contained in the certificate. This tells the application or server that the entity trying to access it is legitimate and known, and should be given access. The certificate contains information regarding the subject of a certificate (the owner) and the issuing certification authority (CA).

X.509 certificates include:

  • Owner’s information or subject distinguished name (DN)
  • Public key associated with the subject
  • Version information
  • Serial number of the certificate
  • Another distinguished name identifying the issuer of the certificate (CA)
  • Digital signature of the CA
  • Information on the algorithm used to create the digital certificate

To ensure the validity of the certificate, it must be signed by a certification authority, which is a trusted node that confirms the integrity of the public key value contained in the certificate. The certificate is signed by the CA by adding a digital signature encoded with the CA’s private key. The CA has a declared public key which is known by all supporting applications and devices, who then validate a certificate by decoding the digital signature within the certificate using the CA’s public key.


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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.