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X.509 is an ITU-Tstandard for digital certificates and authentication services, from which the issuer's name and digital signature are derived. X.509 is part of the X.500 directory service for worldwide, distributed and open systems.

Certificates according to X.509 can also be standardised e-mail certificates, which are used for the secure transmission of e-mails and files and are also used for identification against websites.

Schematic structure of the X.509 certificate

Schematic structure of the X.509 certificate

X.509 uses the abstract description syntax ASN.1 to describe a certificate. It contains the serial number, the issuing authority, the person and server name, the public keyprocedure used and the public key of the person and server. This is followed by the digital signature and the signature of the person or server.

The X.509 standard does not prescribe any particular encryption method; the user can decide for himself which encryption method to use for his public key.

S/MIME and the SSL protocol are based on the X.509 format, which is described in RFC 2459.

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Englisch: X.509
Updated at: 05.07.2016
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