The ICAO Public Key Directory (PKD) serves as a central repository for exchanging the information necessary to authenticate electronic Machine Readable Travel Documents (eMRTDs) such as ePassports, electronic ID cards, and Visible Digital Seals. The primary identity document used in international travel, ePassports, is secured with an integrated closed circuit chip, offering security and facilitation benefits that can only be realized when border control authenticates the chip through ePassport validation. As exchanging the necessary information bilaterally would result in a highly complex and ineffective system, the ICAO PKD provides an efficient solution for states to upload and download the required information, ensuring interoperability, and reliable exchange.
https://www.icao.int:443/Security/FAL/PKD/Pages/default.aspx