Definition - What does X.509 mean?
X.509 is an ITU Telecommunications Standardization Sector (ITU-T) standard used in cryptography to implement public key infrastructure (PKI). Originally specified in 1988, X.509 relates to the use of certificates for digital and Web security.
Techopedia explains X.509
Web browsers access digital certificates to alert users ideas to current security practices that work with the existing domain name system (DNS) and other Internet security protocols. X.509 certificate systems involve a particular structure that contains elements like version, serial number, issuer, validity and public key algorithms. All of this is specifically coded so that IT professionals know where to find a given piece of data.
The use of X.509 is part of an evolving process of network data authentication and encryption privacy. As cyberattackers take advantage of vulnerabilities in certificate and authentication processes and upon the identification of certificate exploits, experts work to strengthen the security of these systems.