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The UK coronavirus contact tracking application is configured to use a different model than that proposed by Apple and Google, despite concerns raised about privacy and performance.
The NHS says it has a way to make the software work “well enough” on iPhones without users having to keep it active and on-screen.
That limitation has posed problems for similar applications in other countries.
Experts from GCHQ’s National Cyber Security Center have assisted the effort.
NCSC indicated that its participation has been limited to an advisory role.
“Engineers have faced several core challenges for the app to meet public health needs and support contact event detection well enough, even when the app is in the background, without unduly affecting battery life,” he said. a spokeswoman for NHSX, the digital health service. Innovation unit.
Centralized pairing
Contact tracking apps are designed to automatically alert people to whether they are at high risk for the virus, based on whether someone else they were recently close to has been diagnosed with it.
They work by recording every time two people are at a certain distance from each other for longer than specified.
When a user registers as infected, a cascade of alerts is automatically sent to all others to whom they may have transmitted, possibly advising them to quarantine and / or test themselves.
Like authorities in many other countries, NHSX has chosen to use Bluetooth wireless transmissions to track each qualifying meeting, and has said that alerts will be sent anonymously, so that users don’t know who triggered them.
You have opted for a “centralized model” to accomplish this, which means that the matching process, which determines which phones to send alerts to, occurs on a computer server.
This contrasts with the “decentralized” approach of Apple and Google, where the matches take place on users’ phones.
Tech giants believe their effort provides more privacy, since it limits the capacity of the authorities or a hacker use computer server logs to track specific individuals and identify their social interactions.
But NHSX believes that a centralized system will give you more information about the spread of Covid-19, and therefore how to evolve the application accordingly.
“One of the advantages is that it is easier to audit the system and adapt it more quickly as scientific evidence accumulates,” Professor Christophe Fraser, one of the epidemiologists who advises NHSX, told the BBC.
“The main objective is to give notifications to people who are at the highest risk of becoming infected, and not to people who are at much lower risk.
“It is probably easier to do it with a centralized system.”
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This approach puts the UK at odds with Switzerland, Estonia and the Austrian Red Cross, as well as a pan-European group called DP3T, which is pursuing decentralized designs.
Germany had been in line with NHSX, but its government announced Sunday that it had switched tactics to a “strongly decentralized approach.”
That leaves France as one of the most vocal defenders of a centralized model.
But hundreds of the country’s crypto and computer security experts have just signed an open letter asking him to reconsider. Dozens of those opponents work for Inria, the institution in charge of building the application.
For its part, the European Commission has indicated that any of the models is acceptable.
“All countries implementing an app should put adoption first, and if it doesn’t work well or dramatically depletes battery life, that can be a deterrent, especially for those with older phones,” said Dr DP3T’s Michael Veale.
Energy impact
Apple and Google intend to launch an API software building block this week to support apps that follow their model.
As an incentive, Apple will allow compatible products to perform Bluetooth-based “handshakes” in the background without hindrance.
The American company is not opposed to NHSX’s own effort, and has supported the British team, but still believes that its own solution is much more energy efficient.
The UK solution involves activating the app in the background every time the phone detects another device running the same software.
Then it executes a code before returning to an idle state. All this happens at high speed, but there is still an energy impact.
In contrast, Apple’s own solution allows correspondence to take place without the application having to wake up at all.
And because handshakes take less time to execute, there should be much less cost to battery life.
Australia is the last country to launch a contact tracking app. He also indicated that he had found a way to bypass Apple’s restrictions, but has since recognized power consumption issues as well as “interference” if users have other Bluetooth and paging apps open.
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