It would only be revealed to your drug dealer or to whoever was in the vicinity.

And to the authoroties, who then promise to not violate that promise.

Except they refuse to be limited by cryptographic means to that.

Why? Because they demand the ability to change their promise in the future ... exact details to be specified. Perhaps “solving drugs” with contact tracing. At which point they have your data, you have zero control, and “your honour we can prove he lied: he was close to that drug dealer 5 times. Further details (such as that this happened in the train station and 5000 other people were also close) cannot be confirmed because that would violate privacy”.

This is the government that got caught letting police officers stalk their ex for 2+ years and then initially arrested the victim for more than 2 weeks when caught. Let’s not pretend they’re above doing this, especially since it’s become increasingly clear this contact tracing is the police’s wet dream.

With any luck, we will create stigma a hundred thousand times more powerful against deliberately helping the virus spread.