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How Apple and Google will let your phone warn you if you’ve been exposed to the coronavirus
Apps that warn about close contact with COVID-19 cases can help relax social distancing rules.
On April 10, Apple and Google announced a coronavirus exposure notification system that will be built into their smartphone operating systems, iOS and Android. The system uses the ubiquitous Bluetooth short-range wireless communication technology.
There are dozens of apps being developed around the world that alert people if they've been exposed to a person who has tested positive for COVID-19. Many of them also report the identities of the exposed people to public health authorities, which has raised privacy concerns. Several other exposure notification projects, including PACT, BlueTrace and the Covid Watch project, take a similar privacy-protecting approach to Apple's and Google's initiative.
So how will the Apple-Google exposure notification system work? As researchers who study security and privacy of wireless communication, we have examined the companies' plan and have assessed its effectiveness and privacy implications.
Recently, a study found that contact tracing can be effective in containing diseases such as COVID-19, if large parts of the population participate. Exposure notification schemes like the Apple-Google system aren't true contact tracing systems because they don't allow public health authorities to identify people who have been exposed to infected individuals. But digital exposure notification systems have a big advantage: They can be used by millions of people and rapidly warn those who have been exposed to quarantine themselves.
Because Bluetooth is supported on billions of devices, it seems like an obvious choice of technology for these systems. The protocol used for this is Bluetooth Low Energy, or Bluetooth LE for short. This variant is optimized for energy-efficient communication between small devices, which makes it a popular protocol for smartphones and wearables such as smartwatches.
Bluetooth LE communicates in two main ways. Two devices can communicate over the data channel with each other, such as a smartwatch synchronizing with a phone. Devices can also broadcast useful information to nearby devices over the advertising channel. For example, some devices regularly announce their presence to facilitate automatic connection.
To build an exposure notification app using Bluetooth LE, developers could assign everyone a permanent ID and make every phone broadcast it on an advertising channel. Then, they could build an app that receives the IDs so every phone would be able to keep a record of close encounters with other phones. But that would be a clear violation of privacy. Broadcasting any personally identifiable information via Bluetooth LE is a bad idea, because messages can be read by anyone in range.
To get around this problem, every phone broadcasts a long random number, which is changed frequently. Other devices receive these numbers and store them if they were sent from close proximity. By using long, unique, random numbers, no personal information is sent via Bluetooth LE.
Apple and Google follow this principle in their specification, but add some cryptography. First, every phone generates a unique tracing key that is kept confidentially on the phone. Every day, the tracing key generates a new daily tracing key. Though the tracing key could be used to identify the phone, the daily tracing key can't be used to figure out the phone's permanent tracing key. Then, every 10 to 20 minutes, the daily tracing key generates a new rolling proximity identifier, which looks just like a long random number. This is what gets broadcast to other devices via the Bluetooth advertising channel.
When someone tests positive for COVID-19, they can disclose a list of their daily tracing keys, usually from the previous 14 days. Everyone else's phones use the disclosed keys to recreate the infected person's rolling proximity identifiers. The phones then compare the COVID-19-positive identifiers with their own records of the identifiers they received from nearby phones. A match reveals a potential exposure to the virus, but it doesn't identify the patient.
Most of the competing proposals use a similar approach. The principal difference is that Apple's and Google's operating system updates reach far more phones automatically than a single app can. Additionally, by proposing a cross-platform standard, Apple and Google allow existing apps to piggyback and use a common, compatible communication approach that could work across many apps.
No plan is perfect
The Apple-Google exposure notification system is very secure, but it's no guarantee of either accuracy or privacy. The system could produce a large number of false positives because being within Bluetooth range of an infected person doesn't necessarily mean the virus has been transmitted. And even if an app records only very strong signals as a proxy for close contact, it cannot know whether there was a wall, a window or a floor between the phones.
However unlikely, there are ways governments or hackers could track or identify people using the system. Bluetooth LE devices use an advertising address when broadcasting on an advertising channel. Though these addresses can be randomized to protect the identity of the sender, we demonstrated last year that it is theoretically possible to track devices for extended periods of time if the advertising message and advertising address are not changed in sync. To Apple's and Google's credit, they call for these to be changed synchronously.
But even if the advertising address and a coronavirus app's rolling identifier are changed in sync, it may still be possible to track someone's phone. If there isn't a sufficiently large number of other devices nearby that also change their advertising addresses and rolling identifiers in sync – a process known as mixing – someone could still track individual devices. For example, if there is a single phone in a room, someone could keep track of it because it's the only phone that could be broadcasting the random identifiers.
Another potential attack involves logging additional information along with the rolling identifiers. Even though the protocol does not send personal information or location data, receiving apps could record when and where they received keys from other phones. If this was done on a large scale – such as an app that systematically collects this extra information – it could be used to identify and track individuals. For example, if a supermarket recorded the exact date and time of incoming rolling proximity identifiers at its checkout lanes and combined that data with credit card swipes, store staff would have a reasonable chance of identifying which customers were COVID-19 positive.
And because Bluetooth LE advertising beacons use plain-text messages, it's possible to send faked messages. This could be used to troll others by repeating known COVID-19-positive rolling proximity identifiers to many people, resulting in deliberate false positives.
Nevertheless, the Apple-Google system could be the key to alerting thousands of people who have been exposed to the coronavirus while protecting their identities, unlike contact tracing apps that report identifying information to central government or corporate databases.
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What is human dignity? Here's a primer, told through 200 years of great essays, lectures, and novels.
- Human dignity means that each of our lives have an unimpeachable value simply because we are human, and therefore we are deserving of a baseline level of respect.
- That baseline requires more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose.
- We look at incredible writings from the last 200 years that illustrate the push for human dignity in regards to slavery, equality, communism, free speech and education.
The inherent worth of all human beings<p>Human dignity is the inherent worth of each individual human being. Recognizing human dignity means respecting human beings' special value—value that sets us apart from other animals; value that is intrinsic and cannot be lost.</p> <p>Liberalism—the broad political philosophy that organizes society around liberty, justice, and equality—is rooted in the idea of human dignity. Liberalism assumes each of our lives, plans, and preferences have some unimpeachable value, not because of any objective evaluation or contribution to a greater good, but simply because they belong to a human being. We are human, and therefore deserving of a baseline level of respect. </p> <p>Because so many of us take human dignity for granted—just a fact of our humanness—it's usually only when someone's dignity is ignored or violated that we feel compelled to talk about it. </p> <p>But human dignity means more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose—a freedom that can be hampered by restrictive social institutions or the tyranny of the majority. The liberal ideal of the good society is not just peaceful but also pluralistic: It is a society in which we respect others' right to think and live differently than we do.</p>
From the 19th century to today<p>With <a href="https://books.google.com/ngrams/graph?year_start=1800&year_end=2019&content=human+dignity&corpus=26&smoothing=3&direct_url=t1%3B%2Chuman%20dignity%3B%2Cc0" target="_blank" rel="noopener noreferrer">Google Books Ngram Viewer</a>, we can chart mentions of human dignity from 1800-2019.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDg0ODU0My9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY1MTUwMzE4MX0.bu0D_0uQuyNLyJjfRESNhu7twkJ5nxu8pQtfa1w3hZs/img.png?width=980" id="7ef38" class="rm-shortcode" data-rm-shortcode-id="9974c7bef3812fcb36858f325889e3c6" data-rm-shortcode-name="rebelmouse-image" />
American novelist, writer, playwright, poet, essayist and civil rights activist James Baldwin at his home in Saint-Paul-de-Vence, southern France, on November 6, 1979.
Credit: Ralph Gatti/AFP via Getty Images
The future of dignity<p>Around the world, people are still working toward the full and equal recognition of human dignity. Every year, new speeches and writings help us understand what dignity is—not only what it looks like when dignity is violated but also what it looks like when dignity is honored. In his posthumous essay, Congressman Lewis wrote, "When historians pick up their pens to write the story of the 21st century, let them say that it was your generation who laid down the heavy burdens of hate at last and that peace finally triumphed over violence, aggression and war."</p> <p>The more we talk about human dignity, the better we understand it. And the sooner we can make progress toward a shared vision of peace, freedom, and mutual respect for all. </p>
Scientists find that bursts of gamma rays may exceed the speed of light and cause time-reversibility.
- Astrophysicists propose that gamma-ray bursts may exceed the speed of light.
- The superluminal jets may also be responsible for time-reversibility.
- The finding doesn't go against Einstein's theory because this effect happens in the jet medium not a vacuum.
Jet bursting out of a blazar. Black-hole-powered galaxies called blazars are the most common sources detected by NASA's Fermi Gamma-ray Space Telescope.
Cosmic death beams: Understanding gamma ray bursts<div class="rm-shortcode" data-media_id="cu2knVEk" data-player_id="FvQKszTI" data-rm-shortcode-id="c6cfd20fdf31c82cb206ade8ce21ba3f"> <div id="botr_cu2knVEk_FvQKszTI_div" class="jwplayer-media" data-jwplayer-video-src="https://content.jwplatform.com/players/cu2knVEk-FvQKszTI.js"> <img src="https://cdn.jwplayer.com/thumbs/cu2knVEk-1920.jpg" class="jwplayer-media-preview" /> </div> <script src="https://content.jwplatform.com/players/cu2knVEk-FvQKszTI.js"></script> </div>
Researchers dramatically improve the accuracy of a number that connects fundamental forces.
- A team of physicists carried out experiments to determine the precise value of the fine-structure constant.
- This pure number describes the strength of the electromagnetic forces between elementary particles.
- The scientists improved the accuracy of this measurement by 2.5 times.
The process for measuring the fine-structure constant involved a beam of light from a laser that caused an atom to recoil. The red and blue colors indicate the light wave's peaks and troughs, respectively.
Scientists at Washington University are patenting a new electrolyzer designed for frigid Martian water.
- Mars explorers will need more oxygen and hydrogen than they can carry to the Red Planet.
- Martian water may be able to provide these elements, but it is extremely salty water.
- The new method can pull oxygen and hydrogen for breathing and fuel from Martian brine.