The International Air Transport Association welcomed the creation by the International Civil Aviation Organization (ICAO) of a global directory of public keys required for authentication of health credentials. The directory—called the Health Master List (HML)—will make a significant contribution to the global recognition and verification (interoperability) of government issued health credentials. A public key enables third parties to verify that a QR code displayed on a health credential is authentic and valid. The HLM is a compilation of public key certificates signed by ICAO and regularly updated as more health proofs are issued and new public keys are required. Its