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The NHS wanted the ability to model "risk-from" a contact, rather than only "risk-to". In the decentralised approach, infected users upload a list of their own
by g_p 6y ago
The NHS wanted the ability to model "risk-from" a contact, rather than only "risk-to". In the decentralised approach, infected users upload a list of their own identifiers, these are broadcast, and everyone checks if they've been near one. There needs to be a threshold picked that will trigger to alert you - probably "contact-minutes" with an infected person.
The NHS approach is less binary, as they believe based on the rate of spread that it's necessary to request people report symptoms and share their own anonymous contact log. Based on the level of exposure the "suspected individual" had with other known/suspected infected people, combined with the number of other known/suspected infected people you were near, your advice can be tailored. You might be told to isolate, but then you're asked to report symptoms regularly. Others in the same position as you will be doing so as well - there is potential here to actually tell people they no longer need to self isolate if the "group" don't have any symptoms emerging, based on the epidemiology and the rate people are believed to develop symptoms in the population.
There's a good write-up of this actually in the NCSC security report and post - https://www.ncsc.gov.uk/files/NHS-app-security-paper%20V0.1.pdf https://www.ncsc.gov.uk/files/NHS-app-security-paper%20V0.1.... and https://www.ncsc.gov.uk/blog-post/security-behind-nhs-contact-tracing-app https://www.ncsc.gov.uk/blog-post/security-behind-nhs-contac.... It explains a lot about the rationale, and not only for security, also in terms of the approach and how the app is designed to work when people have symptoms etc.
- seanwilson 6y agoThanks for that I'll have a read. Is there any discussion about other countries using this NHS app (the repo says MIT license)? Each country could customise the alert heuristic but it seems like a waste of resources for each country to code their own app for a global problem.
- g_p 6y ago> Thanks for that I'll have a read. > Is there any discussion about other countries using this NHS app (the repo says MIT license)? > Each country could customise the alert heuristic but it seems like a waste of resources for each country to code their own app for a global problem. Not seen any other country talking about this yet although it only came out today in source form, and still is technically in limited beta. I imagine Australia and Singapore will be interested in the iOS Bluetooth in sleep workaround method, as that does appear to be novel and not really done before. If you implement the same basic API, it would be easy for another country to implement. The nice aspect of this design is that you can have an MVP (like UK has right now) while you evolve the more complex heuristics and models on the backend, and add those as you develop them. I'd agree it's a waste to build multiple apps, and I imagine countries will be looking at this approach now, and the value of an app with real working code, versus trying to build something. The Bluetooth protocol itself is designed to support multiple countries using it - the outer message contains a country code flag so you know which country's health system you'd need to communicate with in order to exchange info of a proximity event.
- seanwilson 6y ago> the iOS Bluetooth in sleep workaround method Why do they need to find a workaround? Can't Apple tell them the best way or push an iOS patch to help?
- g_p 6y ago> > the iOS Bluetooth in sleep workaround method > Why do they need to find a workaround? Can't Apple tell them the best way or push an iOS patch to help? Apple seem to take the view governments should use their decentralised approach, or not do it, and don't seem to have been willing to help governments do this without using their "joint approach" with Google. I am normally the first to back anything decentralised. But in this case, the stated goals of the app (from a very good NCSC writeup I've linked elsewhere in these comments) simply don't work with a decentralised approach (namely being able to do risk-from calculation, not just risk-to, and being able to gather and model from symptoms whether others should keep isolating or can go back to normal). Given Apple said it wouldn't help anyone not wanting to go "their" way, it's quite reassuring to see that engineers do what they do best, finding a new workaround, and making details of it available for any other devs... Perhaps Australia can use this in their app now to fix their issues with Bluetooth and iOS.
- lozenge 6y agoThe Bluetooth message includes the country code unencrypted, this allows the system to interoperate with others. Every country will want its own data store at a minimum.