Interoperability hackathons showcase the benefits of open source and community and drive scale

By Trevor Butterworth

The growth in open source software has been driven by a simple, powerful value proposition: more means more. The more people use an open source solution, the better the solution becomes through stress testing and innovation; the better it becomes, the more it will scale because more people will want to use it.

This can happen organically—or it can happen through a community pushing itself to adopt, adapt, and scale. This was the idea behind the first Cardea Interop-a-thon.

Cardea is a complete open-source codebase for creating, sharing, and verifying digital health credentials with a focus on COVID-19 testing and vaccination; it was developed by Indicio and SITA and donated to Linux Foundation Public Health (LFPH), where its continued development is overseen by a community of companies and interested parties, including Indicio and SITA.

As the concept of verifiable digital credentials requires interoperability to scale, we decided that the best way to drive interoperability was to set up a reference implementation of Cardea and invite other companies using Hyperledger Aries-based solutions to test against it and each other.

It was a success. The six companies that participated in the virtual event all achieved their goals. It wasn’t painless—and that was the point. Glitches, bugs, and unknown obstacles were all uncovered by the concerted focus on testing against each other. The result is that everyone  emerged with better products.

The reaction was, “we need more of this!” And so, this week, on March 17, we will host our second Cardea Interop-a-thon. We’ll have the standard reference implementation to test against, but we’ll also have two new and important features: out-of-band invitations and machine readable governance.

Out-of-band (OOB) invitations use the new out-of-band protocol for creating a connection using an invitation URL or QR code. The first phase is coming to Hyperledger Aries at the end of March (see the transition plan) and the community will proceed until the full OOB invitation process is supported as the default connection method (to read more, see the Aries RFC).

Machine-readable governance is a way to implement governance rules at the agent level; it makes the governance authority portable. Why is this important?

First, it means that governance rules can be cached and verification can happen offline.

Second, it means that complex information flows with “if this, then that” logic become simpler to choreograph than if governed by a central trust authority; bonus, they can be kept private too (for more on the benefits of machine-readable governance, see “Machine Readable Governance is the Key to Scaling Decentralized Trust.”)

Registration is closed, and we’ve got over twice as many participants for our second Interop-a-thon; but you’re more than welcome to show up and watch! Visit for details.