Connecting the world and beyond

Fourth ITU-T X.509 Day

The International Telecommunication Union (ITU) organized the Fourth ITU-T X.509 Day which took place virtually on 5 September 2025 from 13h00 to 16h00 CEST.

ITU-T X.509 is the common global language for public key infrastructure (PKI) and privilege management infrastructure (PMI) – the fundamental framework for digital certificates and trust management. First published in 1988, the result of collabaration between ITU and ISO/IEC, ITU-T X.509 has evolved through nine editions (the latest approved in October 2019). A tenth edition is currently under study to address emerging needs such as quantum-safe cryptography.

The X.509 certificate and the Certificate Revocation List (CRL) structures, known for their extensibility, underpin secure transactions in business-to-business (B2B), business-to-consumer (B2C), and government-to-citizen (G2C) interactions. This robust standard provides a reliable foundation for a wide range of industries – from agriculture and finance to healthcare, transport, and utilities – and is vital to businesses, consumers, and governments worldwide.

With over 37 years of successful implementation, X.509 has become a universal enabler of interoperability and security in countless applications. To honour its legacy, ITU has been organizing ITU-T X.509 Day events since 2022, celebrating the standard's enduring impact and achievements each year.

The objectives of this fourth ITU-T X.509 Day (2025) event included:

Reviewing the progress of ITU-T X.509 since the third ITU-T X.509 Day in 2024, including updates from ongoing work and collaborations;
Assessing post-quantum cryptography (PQC) readiness in the X.509 ecosystem;
Exploring developments in decentralized PKI (DPKI) and trust models;
Discussing cross-border digital identity frameworks and global trust networks, highlighting how X.509 certificates enable interoperability of digital identities across borders and sectors;
Strengthening trust in AI-enabled systems by leveraging X.509;
Showcasing real-world adoption across sectors through case studies;
Identifying future development directions for ITU-T X.509 and opportunities for collaboration.

Target audience

Participation was free of charge and open to all interested stakeholders including ITU Member States, Sector Members, Associates and Academic Institutions and to any individual from a country that is a member of ITU and who wished to contribute to the work. The event was organised in English only.

Watch recording of the session here