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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:
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.
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:
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.