EU member states in the eHealth Network agreed on guidelines that describe the main technical specifications for the implementation of Digital Green Certificate, the EU-wide digital COVID-19 passport. The announcement noted that it is critical to advance the work of the technical implementation, in parallel with the ongoing legislative process, to ensure a rollout of Digital Green Certificate across the EU by June 2021. The agreed technical specification covers data structure and encoding mechanisms, including QR codes. This is to ensure that all certificates, whether it is digital or paper-based, can be read and verified across the EU. The guideline also introduces the EU gateway, which will be set up by the European Commission and allow the sharing of electronic signature keys so that the authenticity of Digital Green Certificates can be verified across the EU. There is no personal data of certificate holders will travel through the gateway, as they are not necessary for the verification. Furthermore, the guidelines explain reference implementations for software to issue Digital Green Certificates, a reference app to verify certificates, and a template for a wallet app for citizens to store them. Member states are responsible for setting up these systems at national level, however the reference implementations will help accelerate the deployment as it allows member states to build upon them. The reference implementations will be open source and available by mid-May 2021.