There are only two real ways to implement that. One is the "attribute certificate" is still tied to your full identity and then people won't be willing to associate them. The other is that the attribute certificates are fully generic (e.g. everyone over 18 gets the same one) and then someone will post it on the internet and, because there is no way to tie it back to a specific person, there is no way to stop them and it makes the system pointless.
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There are only two real ways to implement that. One is the "attribute certificate" is still tied to your full identity and then people won't be willing to associate them. The other is that the attribute certificates are fully generic (e.g. everyone over 18 gets the same one) and then someone will post it on the internet and, because there is no way to tie it back to a specific person, there is no way to stop them and it makes the system pointless.