We can modify our ZK credential to support a limit of N shows as follows. First, let’s have the User select a random key K for a pseudorandom function (PRF), which takes a key and an arbitrary input and outputs a random-looking outputs. We’ll embed this key K into the signed credential. (It’s important that the Issuer does not learn K, so this often requires that the credential be signed using a blind, or partially-blind, signing protocol.3) We’ll now use this key and PRF to generate unique serial numbers, each time we “show” the credential.
1. 居家适老化改造（防滑地板、扶手、智能监测）。电影对此有专业解读
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Получивший взятку в размере 180 миллионов экс-мэр российского города обратился к суду14:53，详情可参考电影
В России предупредили о подготовке ВСУ к контратаке на одном направлении08:42
Фото: Gwent Police