In 1996, version 3 of the standard provided a major update with the addition of multiple extensions that are still used today to support the expansion and new applications of internet use. Looking to formalize the rules for certificate issuance, the Telecommunication Standardization Sector of the ITU (ITU-T) developed a hierarchical system for distinguished names that followed the electronic directory service rules for X.500 and was inspired by the systems used to assign telephone numbers globally but applied to the more flexible organizational requirements of the Internet. The first version of the X.509 standard was published back in 1988.

But the X.509 protocol is also applied to code signing for application security, digital signatures, and other critical internet protocols.

The most common use case of X.509-based PKI is Transport Layer Security (TLS)/Secure Socket Layer (SSL), which is the basis of the HTTPS protocol, which enables secure web browsing. Applied to cryptography, the public and private key pair is used to encrypt and decrypt a message, ensuring both the identity of the sender and the security of the message itself. One of the structural strengths of the X.509 certificate is that it is architected using a key pair consisting of a related public key and a private key. They are unobtrusive and ubiquitous, and we encounter them every day when using websites, mobile apps, online documents, and connected devices. They are used to manage identity and security in internet communications and computer networking. An X.509 certificate is a digital certificate based on the widely accepted International Telecommunications Union (ITU) X.509 standard, which defines the format of public key infrastructure (PKI) certificates.

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