[Slartie]

His argument is self-defeating. If you have rapid exponential growth and would have to publish hundreds of megabytes of keys per day, this approach of contact tracing is useless and you must instead get the entire population under lockdown. If everybody is sheltering at home, nobody needs notifications of possible contacts, because everybody is doing what would be the response to such a notification already.

This approach, just like the manual approach of tracking potential contacts via paper and phone, is only of use in a scenario with a very limited number of transmissions and an R (reproduction rate) of around or below 1. Its purpose is not to reach such a situation, but to aid in keeping that situation in effect without severe measures. But severe lockdowns must first suppress the infection counts to such levels before any contact tracing may work at all.