  In order to contain the COVID-19 pandemic, several countries enforced
extended social distancing measures for several weeks, effectively pausing the
majority of economic activities. In an effort to resume economic activity
safely, several Digital Contact Tracing applications and protocols have been
introduced with success. However, DCT is a reactive method, as it aims to break
existing chains of disease transmission in a population. Therefore DCT is not
suitable for proactively preventing the spread of a disease; an approach that
relevant to certain use cases, such as international tourism, where individuals
travel across borders. In this work, we first identify the limitations
characterising DCT related to privacy issues, unwillingness of the public to
use DCT mobile apps due to privacy concerns, lack of interoperability among
different DCT applications and protocols, and the assumption that there is
limited, local mobility in the population. We then discuss the concept of a
Health Passport as a means of verifying that individuals are disease risk-free
and how it could be used to resume the international tourism sector. Following,
we present the DHP Framework that uses a private blockchain and Proof of
Authority for issuing Digital Health Passports. The framework provides a
distributed infrastructure supporting the issuance of DHPs by foreign health
systems and their verification by relevant stakeholders, such as airline
companies and border control authorities. We discuss the attributes of the
system in terms of its usability and performance, security and privacy.
Finally, we conclude by identifying future extensions of our work on formal
security and privacy properties that need to be rigorously guaranteed via
appropriate security protocols.
