With the DP3T derivable day keys, you could identify that you were actually in contact with the same infected person multiple days. If the server ships 14 * (#

With the DP3T derivable day keys, you could identify that you were actually in contact with the same infected person multiple days. If the server ships 14 * (# of people infected) every day to every user, instead of just (# of people infected) and have the client generate the 14 keys for each infected person, you would only be able to identify that you were in contact with an infected person. With the DP3T proposal, it looks like you can identify that you were around the same infected user multiple days, which might be slightly worse for privacy (in the sense that it would help you identify who you got it from). But in either case, because the secret key is reset after being made public, it would not help you identify who was previously infected.