How contact tracing apps can stop both COVID-19 and Big Brother

Comic by Nicky Case. Story made with Tappable.

A problem with COVID-19: it takes about 5 days for the first symptoms to show up, 2 days of which you are contagious.

So if we quarantine folks exposed to you from the day you're diagnosed...

... we stop the spread, by staying one step ahead!

*what about never-symptomatic people? Turns out they don't play a large role in COVID-19 spread! See citations at end

This is called "contact tracing". It's a core part of how South Korea & Taiwan are already containing COVID-19. It is what we should do, too.

We don't even need to find all the contacts! Finding about 60% of them is enough ...

* ~60%? again, see citations at the end!

... but we do need to find them quickly. Traditional contact tracing, with interviews, is too slow.

Hence, why we need contact tracing apps.

But do we have to sacrifice privacy for health?

It's entirely possible to

protect peoples' lives AND liberties, with a really simple process!

Let's see how it works,

with the help of

Alice & Bob

Alice gets a tracing app! Its code is open to the public. She can verify that it does the following...

Every 5 minutes, her phone sends uniquely random messages to all nearby devices, using Bluetooth.

* 5 minutes is just an example! and technically it's "pseudo-random," since it's not quantum ... does NOT matter.

These random messages contain NO INFO about Alice's identity, location or anything. The app does not use GPS.

While her phone sends out random messages, it also listens for similar random messages from nearby phones.

Bob also has a privacy-first tracing app. It may be the same as Alice's or one that is compatible.

If Alice & Bob stay close to each other for more than 5 minutes, their phones will exchange unique messages.

Both their phones will remember all the messages they "said" and "heard" over the last 14 days.

Again: because the random messages contain NO INFO, Alice's privacy is protected from Bob, and vice versa!

* 14 days is also just an example! Epidemiologists may learn that the "infectious period" is actually shorter or longer.

The next day, Alice develops a dry cough and fever.

Alice gets tested.

Alice has COVID-19.

It is not a good day for Alice.

As soon as she is diagnosed, 

Alice uploads her "What I Said" messages to a hospital database. She uses a one-time passcode given by her doctor.  The code is to prevent spam.

Alice can keep messages private. like for instances the evenings she spent at home.

The database stores Alice's messages:

These messages are meaningless to the hospital. They don't say where Alice was, who she was with, what they were doing or how many people she met. 

* different countries hospitals could exchange messages, but

because they contain no info, no privacy is lost.

... but they are very meaningful to Bob!

Bob's phone, regularly checks the hospital's database of random messages from COVID-19 cases.  It checks if it "heard" any of them from nearby phones in the last 14 days.

NO PERSONAL INFO is exchanged.

* the real DP-3T protocol is even MORE secure! it uses a "cuckoo filter" so phones know ONLY the covid-19 messages, they heard, without revealing ALL covid-19 messages.

If Bob's phone heard 6 or more COVID-19 cases' messages, he is warned to self-quarantine. That's after 6 x 5 min = 30 minutes of total exposure. 

And thus, Bob cuts the chain of transmission - one step ahead of the virus!

* again, these numbers are just examples!

And that's it!

That's how digital contact tracing can proactively prevent the spread of COVID-19 while also protecting our rights.

Thanks, Alice & Bob!

Stay safe.


This comic was made by Nicky Case and published in the Public Domain.

The comic has been adapted to a Story format by the team at Tappable. Create your own Web Stories by signing up for early access on

This comic is a rough summary of the DP-3T protocol, as of April 9th, 2020. The real thing is more complex and even more secure!

And finally, share this story widely!