We propose the concept of "zk-SBT"—a zero-knowledge soulbound token. A zk-SBT has an open part and a secret part. The open part is a non-transferable NFT. The secret part is a verifiable credential. The two parts are linked by storing the hash/CID of the credential in the NFT. A zk-SBT can be minted by a trusted party and bound to the address of a receiver to represent a transfer of trust. E.g. a city hall can mint an identity zk-SBT to a citizen. The NFT shows "Residence Permit". The credent...