The ICAO Public Key Directory (PKD) is a central repository for exchanging the information required to authenticate electronic Machine Readable Travel Documents (eMRTDs) such as ePassports, electronic ID cards and Visible Digital Seals.
 
ePassports play a particular crucial role as the principle identity document used in international travel. The security and facilitation advantages of ePassports are grounded in the presence of an integrated closed circuit chip. However, those benefits can only be realized when border control authenticates the chip. If the chip is not authenticated at border control, the ePassport has little advantage over a traditional, non-electronic passport. 
                                                                                               
This authentication — usually referred to as ePassport validation—is the process of validating the authenticity and integrity of an ePassport by verifying the digital signature on the chip. 
 
For the border control of a receiving State to authenticate the ePassport of a foreign traveler, the receiving State must have access to certain information from the issuing State. Should states only have the option to exchange the necessary information bilaterally, the volume of information being exchanged would result in a highly complex and ineffective system that would be susceptible to errors. The ICAO PKD provides an efficient means for States to upload their own information and download that of other States.
 
By playing the role of central broker for this information, the ICAO PKD ensures that information adheres to the technical standards required to achieve and maintain interoperability. In addition, the ICAO PKD ensures that information can be exchanged reliably, in a timely manner and on an open-ended, indefinite basis. Read the ePassport Basics section to learn more about the kinds of information needed to conduct ePassport validation.