Analysis The UK has decided to break with growing international consensus and insist its upcoming coronavirus contact-tracing app is run through centralised British servers – rather than follow the decentralized Apple-Google approach.

In a blog post just before the weekend, the CEO of the National Health Service’s tech unit NHSX Matthew Gould, and the app’s main overseer Dr Geraint Lewis, said their new smartphone application will launch “in the coming weeks,” and stressed it “could be important in helping the country return to normality and beating coronavirus.”

But within the details over how it would work, the memo revealed the NHS and UK government reckon the contact-tracing protocols built by Apple and Google protect user privacy under advisement only. Thus, the British health service is in favor of a system that sends data on who may have the virus to a centralised server, and puts the NHS in charge of who is contacted and when.

Both techniques, Apple-Google and NHS, rely on Bluetooth: simply put, your phone wirelessly emits an electronic ID that other phones will pick up when they are in close proximity. If someone tests positive for COVID-19, their ID will be used to alert others who have been near them: an ID will be flagged as infected, and if you've been near that ID, then you may have caught the novel coronavirus, too, and will be warned as such.

Apple and Google, specifically, created an opt-in pro-privacy API for iOS and Android that allows your phone to periodically change its ID as well as store the IDs of other phones it comes close to. Then, if someone is found to have COVID-19, they can authorise the release of their phone’s IDs to a decentralized set of databases managed by healthcare providers, and if another user’s phone recognizes those IDs in the databases – ie: they were close to them recently – they are alerted to the fact by apps that plug into the API.

This particular approach is designed to ensure no one can use it to track individuals: Apple and Google reckon their cryptography-based protocol will make it difficult for governments and miscreants to monitor people – certainly Apple and Google will be none the wiser. Data stays on people's phones, and is only released to providers' databases when the user wants to. And they stay anonymous. To declare yourself infected, you need to enter a special code from a healthcare provider after testing positive – otherwise trolls could derail the system by falsely announcing themselves infected en masse.

An analysis by Brit developer David Llewellyn-Jones, among others, shows this is a decent enough solution, though a point of failure is the apps themselves that plug into the API: they cannot be allowed to siphon off sensitive information gleaned from the contact-tracing protocol.

As an alternative to all of this, the NHS proposes using a centralized approach, in which everyone's whereabouts and any other information is simply uploaded to a government-owned database and analyzed there.

Uptake

Experts say that for a contact-tracing app to be effective, about 60 per cent or more of the population will need to download it on their phones and opt-in. As a result, privacy concerns are critical to the app’s success: if people don’t trust it, they won’t install it.

While there are some advantages and disadvantages to a centralised NHS and decentralised Apple-Google model, the fact that high adoption is critical has led a slew of countries including Switzerland, Estonia, and Austria plumping for the decentralised privacy-protecting approach.

In addition, Germany has backtracked on its plans to run a centralised service, saying on Sunday it will switch to a "strongly decentralised approach," and France – which insisted on a centralised approach – is facing growing backlash from security experts, many of whom have signed a letter opposing its plans.

Apple and Google tweak key bits of contact-tracing privacy plan READ MORE

Despite this, however, the NHS has rejected the decentralised approach in favor of putting itself in control. The NHS app will grab all the IDs of all phones running the app, and store and process it all on its own servers. Then, if someone finds they have the virus and tells the app, whoever is in charge of the NHS database will decide how, when, and if, to alert other phones.

The NHS has been keen to stress that it will protect people’s privacy despite effectively granting itself real-time location tracking. “The data will only ever be used for NHS care, management, evaluation and research,” the blog post stated.

“You will always be able to delete the app and all associated data whenever you want. We will always comply with the law around the use of your data, including the Data Protection Act and will explain how we intend to use it.

“We will be totally open and transparent about your choices in the app and what they mean. If we make any changes to how the app works over time, we will explain in plain English why those changes were made and what they mean for you. Your privacy is crucial to the NHS, and so while these are unusual times, we are acutely aware of our obligations to you.”

Yes, but why?

The obvious question however is: why? Why take this approach at all, especially when the rest of the world is moving toward a decentralised approach?

The answer appears to be that those in charge think it will work better. “The app will advise you what action to take if you have been close to someone who has become symptomatic – including advising you to self-isolate if necessary,” the blog post stated. “The exact advice on what you should do will depend on the evolving context and approach.”

In other words, rather than simply receive an alert that will, presumably, be hard-coded into the app itself, the centralised server approach would, in theory, allow the NHS to send more personalised messages. It goes on: “Scientists and doctors will continuously support us to fine-tune the app to ensure it is as helpful as possible both to individuals and to the NHS in managing the pandemic.”

Whether that is a theoretical advantage or a pragmatic one is hard to know. If the NHS was swamped with hundreds of thousands or even millions of alerts, it would likely have to resort to automated default responses regardless.

Another reason put forward by the NHS is that it wants the ability to build a more extensive database, through app updates, in which additional data is provided by individual users but can then be attached to existing profiles in the centralized database and so help health professionals deal more effectively with the virus.

“In future releases of the app, people will be able to choose to provide the NHS with extra information about themselves to help us identify hotspots and trends. Those of us who agree to provide this extra information will be playing a key role in providing additional information about the spread of COVID-19 that will contribute towards protecting the health of others and getting the country back to normal in a controlled way, as restrictions ease.”

Lower risk

One of the epidemiologists working on the project, Professor Christophe Fraser, told the BBC on Monday: "One of the advantages is that it's easier to audit the system and adapt it more quickly as scientific evidence accumulates… The principal aim is to give notifications to people who are most at risk of having got infected, and not to people who are much lower risk. It's probably easier to do that with a centralised system."

But the end result is that the NHS plans to do exactly what people are concerned about: build a highly specific database of people, their movements and the health status, and have it populated by automated data uploads from anyone who has installed the app.

It will be a major test of how much people trust the NHS with their personal information, and how much they trust the UK government not to copy or exploit that data in future for different purposes. ®

PS: This was a fear the NHS app would burn through people's batteries by using Bluetooth – whereas the Apple-Google interface runs minimally in the background. However, it appears the NHS has found a compromise in that it will run its app intermittently in the foreground.