The idea is to leverage information from site A (say, a bank) who knows a lot about the user to attest to site B (say, HN) that the user is a real person, witho

The idea is to leverage information from site A (say, a bank) who knows a lot about the user to attest to site B (say, HN) that the user is a real person, without revealing any other information known by site A to site B.