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Issue link: https://digital.macdirectory.com/i/1256627
Bluetooth beacons 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. Anonymous exchanges To get around this problem, ever y 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.