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First look at Apple/Google contact tracing framework
41–50 of 113 posts
Re: First look at Apple/Google contact tracing framework
#42The system doesn't need to ship every key to every phone, much more compact structures like Bloom filters could be used instead. If we assume about 1000 positives per day and each positive uploading 14 days of keys at 4 keys per hour that's a bit over 1 million keys per day. A Bloom filter with a false positive rate of 1/1000 could store that in about a megabyte. Phone downloads the filter each day and checks its obs…
The main issue of bloom filters is this: > only needs to download the actual keys if there's a potential match. One of the design constraints of the service was that it should not know your (suspected) infection status unless you give consent that it should be shared. > Matches must stay local to the device and not be revealed to the Diagnosis Server. https://covid19-static.cdn-apple.com/applications/covid19/cu... Th…
I see lots of ways to mitigate requesting the keys from disclosing much information:
- could set the false positive rate higher than the chance of encountering a case in the wild (which makes it smaller)
- phone could be programmed to sometimes randomly request keys even when the filter doesn't match
- keys could be distributed across many static mirrors and your phone could pick one at random if the filter matched
Re: First look at Apple/Google contact tracing framework
#43> Published keys are 16 bytes, one for each day. If moderate numbers of smartphone users are infected in any given week, that's 100s of MBs for all phones to DL. Seems like a usecase for bloom filters or k-anonymity.
Can you expand on that a bit more? Is the set running and updated locally or centralized?
If local, does it solve the size issue?
Thanks!
Re: First look at Apple/Google contact tracing framework
#44Finally a decent use-case for blockchain and nobody is paying attention. Seems to make a lot more sense to reconcile location and proximity from a shared user-controlled anonymous ledger.
Re: First look at Apple/Google contact tracing framework
#45Regardless of the technical issues with this, I think the "prank" issue Moxie brings up is much more serious. We've already seen the phenomenon of "Zoom bombing", I can imagine "tracer bombing" would be a much more serious issue. The only way I could see this working is that if when you enter a positive result you have to enter some sort of secret key from the testing authority, but that's totally not tenable given a…
Why wouldn't the patient provide their framework info (if they so chose) at the time of sample collection? Then the medical authority could report it to the local government on the patient's behalf in the event of a positive test. Other end users then decide which (if any) "reporting authorities" to pull data from and check against. This also seems to address Moxie's concern about public location data being necessary…
My understanding too was that there was a middleman involved in collecting and distributing the keys, to avoid people spamming the system. You want to be 100% sure it's a positive, and not put the trust in the user. Otherwise random people could just say they have it. The local government would have to submit the keys as you mention and act as moderators for that region.
Re: First look at Apple/Google contact tracing framework
#46> Published keys are 16 bytes, one for each day. If moderate numbers of smartphone users are infected in any given week, that's 100s of MBs for all phones to DL. Seems like a usecase for bloom filters or k-anonymity.
This calculation doesn't make sense to me. Since the start of the pandemic, there's been 1.6m confirmed cases so far worldwide. Even if every single one of those were to send 16 bytes identifier, that would still only be 27MB, no?
Where are they getting 100s of MBs per week? I know it's exponential growth and the number of cases will grow, but their calculation still seems off to me.
EDIT: I guess each person has 14 keys, so that makes it an order of magnitude bigger.
Re: First look at Apple/Google contact tracing framework
#47Earlier quoted context omitted.
I think it may differ by region. I can say factually that the testing in Texas is absolutely abysmal. Many people who have lots of symptoms are being turned away for testing. On Tuesday our illustrious governor announced with lots of fanfare that Walgreen's would be expanding drive-thru testing using Abbott's 15-minute testing devices. It's now Friday evening and still no word on even where the locations will be for…
This may be a bit of an optimistic take, but there's at least some evidence the IFR is ~0.37%. Given the current number of deaths in NYC, that would imply at least ~20% of the city population has already been infected, likely more given the lag between infection and death. If that's true, the best strategy will probably be to keep vulnerable groups isolated and loosen some restrictions until herd immunity is reached.…
Further to this, once we have antigen tests rolling out en mass it will give us a much clearer picture as to how many people have been infected (and are now hopefully immune). Until then we just need to sit back and wait.
Re: First look at Apple/Google contact tracing framework
#48Earlier quoted context omitted.
Why wouldn't the patient provide their framework info (if they so chose) at the time of sample collection? Then the medical authority could report it to the local government on the patient's behalf in the event of a positive test. Other end users then decide which (if any) "reporting authorities" to pull data from and check against. This also seems to address Moxie's concern about public location data being necessary…
My understanding too was that there was a middleman involved in collecting and distributing the keys, to avoid people spamming the system. You want to be 100% sure it's a positive, and not put the trust in the user. Otherwise random people could just say they have it. The local government would have to submit the keys as you mention and act as moderators for that region.
> The local government would have to submit the keys as you mention and act as moderators for that region.
There's a big difference between a centralized and decentralized model here.
* Centralized, there's a single (or only a few) worldwide APIs that you need approval to work with. This also hinders interoperability of different end-user app implementations.
* Decentralized, anyone can set up a distribution server and require whatever authentication they'd like for it. A local government, a hospital, the Red Cross, etc. The framework becomes nothing more than a decentralized protocol that can potentially even be repurposed for other novel uses.
For the decentralized approach, bear in mind that there's nothing preventing a third party from hosting and managing a distribution server on behalf of someone else. So (for example) the CDC could host a server (and handle authentication) for a state or county government that didn't feel up to the task.
Another example, say the local hospital has their own database (possibly hosted by the state or Google or whoever). They can feed their (authenticated, locally collected) data to a local authority (the city or county), which only needs to accept data from trusted institutions (ie all the hospitals in the area). They can in turn feed this inherently trustworthy data to a state system, and so on. If each entity in this hierarchy makes their dataset publicly available, then users can independently decide which datasets are relevant to them (perhaps they traveled recently?) and check them on a daily basis.
Re: First look at Apple/Google contact tracing framework
#49> Published keys are 16 bytes, one for each day. If moderate numbers of smartphone users are infected in any given week, that's 100s of MBs for all phones to DL. Seems like a usecase for bloom filters or k-anonymity.
16 byte keys for a quarter million people are only 4mb per day.
We aren’t seeing remotely close to a quarter million infections per day. The data sizes are reasonable, even if you multiply it times n days for the backward tracing.
I think his post is a little bit more fearmongering than is necessary.
Re: First look at Apple/Google contact tracing framework
#50Regardless of the technical issues with this, I think the "prank" issue Moxie brings up is much more serious. We've already seen the phenomenon of "Zoom bombing", I can imagine "tracer bombing" would be a much more serious issue. The only way I could see this working is that if when you enter a positive result you have to enter some sort of secret key from the testing authority, but that's totally not tenable given a…
It also assumes that if you get a notification of having been near a COVID positive individual that you'll be prudent enough to self isolate.
It doesn’t need to be everyone involved in opting in to tracing, or everyone notified to comply with the self-isolation recommendations to reduce the r0. It works even with only partial penetration of the populace.