Horizen - ZK-SNARK private Corona App

Dear all, I am indirectly involved with one of the teams in the Netherlands working on a private Covid-19 tracking App an assignment/call from the Dutch government. The idea is to store close contact encounters with others by sensing proximity via their Bluetooth signal of mobile phones and subsequently exchanging addresses to mark an encounter. If you or one of the people you interacted with is tested positive with Covid-19, the App can privately notify all the people you recently interacted with by sending them a message/transfer so they know they should be tested.

There are currently two possibilities we are considering for the notification part 1) Sending a notification via the Lightning Network. Since the LN uses onion routing without exit nodes, such a message/transfer would be very private except that you see the address of the sender. Alternatively, 2) I opted that we could use ZK-SNARK shielded transaction to make anonymous message/transfer to notify people in an anonymous way that they had contact with someone carrying Covid-19.

To understand if the second option is feasible, I would like to ask if it is possible to make a SK-SNARK shielded transaction with only a mobile wallet? I also would like to know if there are people on the Horizen team who are available for a collaboration on this @finpunk . The developers themselves are most knowledgeable on Bitcoin, Elements and Lightning. But if shielded transactions can be made from a mobile wallet, I think a solution using ZK-SNARK and possibly running on Horizen (ZEN) or a side chain would be an even more elegant solution. Ideally a transaction or notification would not even show who the sender is of that notification which I think is possible with ZK-SNARK but not with lightning transactions where the receiver will see the address of the sender.

Looking forward to hearing any suggestion or opinions.

Update: I just red the latest post by @finpunk at

I understand Horizen does not have the resources right now to work on such an App. Stay ZEN and work on the core such as working towards the first side chains applications. I cannot wait to see it all come together this year. I just wished I had more fiat since it is a great time to buy more ZEN.


hi @norin very much appreciate the thought! The short answer is we still don’t yet have the capability of doing SNARKs on mobile, but the tech is collapsing in computational costs and will certainly get there in the relatively near future.

I have a feeling contract tracing is going to be a part of our new reality for some time, so the privacy community has to dive head first into this and provide tools for society that provably preserve privacy in the process. Can we have both security and privacy? We better! Because the consequences of society giving up so much are too high.

That said, ginger-lib and the tools that’ll be available for data privacy in our sidechain system go a long way in the right direction. I have no doubt we’ll find ways to radically collapse computational costs for privacy and make it widely available in products.

We’re about a month away from the sidechain Beta SDK, which will let devs start to experiment with the tools. This is so important for us and why we’re all-in on making that a reality ASAP. From there, we’ll need to count on brilliant teams of devs elsewhere to bring useful products to market!