Contact tracing: bluetooth could malfunction in an urban environment

Contact tracing: bluetooth could malfunction in an urban environment Cybersecurity

The saga of the NHS contact tracing application is still far from its end. Fiona Twycross, deputy mayor in London, questioned the ability of this technology to work reliably in busy urban environments, adding that she did not expect the application to be ready before autumn.

Originally scheduled to launch nationwide at the end of May – the same time as StopCovid in France – the application suffered a series of delays and could not be launched as planned on 1er June. The British government has not yet proposed a new launch date.

The application currently under test

A minister recently announced that the technology would be ready this month, while the spokesperson for the Ministry of Health and Social Services (DHSC) interviewed by ZDNet only replied that the tool would be “soon” deployed nationwide.

This contact tracing technology is currently being tested on the Isle of Wight, where it has been downloaded by 54,000 residents. But at a meeting in London, Fiona Twycross explained that even if the application worked on the island, it would not necessarily mean the same result in different contexts.

“It must be done right,” urges the deputy mayor. “We can all imagine what would happen in the context of a large tower, when you rely on bluetooth technology: it is possible that the readings obtained are inaccurate, or that people who were not in contact with others hear that they have been in contact with them. “

Bluetooth rather than geolocation

Bluetooth is used as the backbone of contact tracing applications, to allow smartphones to pick up proximity signals and anonymously record that they have approached other devices. If a person is infected, the affected users registered with the application are alerted and are advised to return home and isolate themselves.

Unlike GPS or Wi-Fi, bluetooth signals only track devices that have been close to each other, rather than the actual location of users. This technology has therefore been presented as a more privacy-friendly solution.

Experts warned, however, that the technology will fail to identify meaningful contact between users. When it comes to estimating distance, the strength of the bluetooth signal lacks precision, which means that bluetooth-based contact finders could report interactions that do not involve risk.

Bluetooth imprecision

A recent study published by Trinity College Dublin has shown that signal strength varies depending on many factors, including how the device is held, whether it is placed in a purse or pocket, or if it’s inside or outside. In addition, bluetooth does not pick up walls and windows – even though they prevent the virus from spreading.

In the case of a high-rise apartment building in a large city, the application can pick up the signal from a device located in a neighboring apartment or on another floor. This could then trigger an avalanche of false positives, warning users to isolate themselves, even if there is no risk of infection.

Aidan Fitzpatrick, CEO of the data company Reincubate, which has studied how the application works, explains to ZDNet that “bluetooth cannot effectively assess barriers or shields.” If we take adjacent rooms separated by a plasterboard wall, they share an excellent bluetooth connection. There will then be false positives in these cases. ”

No official results following the tests carried out

For the moment, no official results concerning the tests of contact tracing on the Isle of Wight have been published. Asked about the reasons for the constant postponement of the national launch date of this technology, the Minister of Health Matt Hancock said that the application works and that the delays are not due to “technical concerns”.

At the same time, the press indicates that the main reason why the initiative has not yet been rolled out nationally comes down to the problems caused by bluetooth signals.

Ross Anderson, professor of security engineering at the University of Cambridge, who is part of a group of people consulted by the NHS on the confidentiality and security of contact tracing applications, confirms to ZDNet that the risk of these applications create far too many false positives: “the problem is intrinsic to bluetooth. There are a ton of variables. So yes, if you live with 80 other people in a tower, bluetooth won’t see the difference. ”

Contact tracing is developing in Europe and worldwide

Several European countries have already launched their own version of the tool. Some of these applications have been developed by the country, as is the case for StopCovid and the future British application, while others are based on the API offered jointly by Google and Apple, which also uses bluetooth signals. .

“Whatever the framework used, that of Google and Apple or that of the NHSX, the problem is the same since it comes from bluetooth. The question is not which framework to use, but whether contact tracing is really a relevant solution, ”questions Aidan Fitzpatrick.

With usage levels remaining fairly low for the moment, it is difficult to assess the success of these bluetooth-based tools. In Singapore, for example, only a fifth of the population has adopted the national TraceTogether app, which has been available for several months. In France, only 2% of the population have downloaded StopCovid since June 3, when the application was launched.



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