The Hydra-S1 proving scheme is the first proving scheme in the Hydra family:

  • Hydra = using Hydra Proof of Ownership via the Commitment Mapper

  • S1 = single source, version 1: verifying membership in a single Data Group

Currently, the proving scheme is utilized by the ZK Badge protocol, which is no longer maintained. It allows users to verify membership in a Data Group from a single Data Source and mint a ZK Badge on an unlinked Ethereum address.

Sismo’s ZK Badge protocol uses Hydra S1 proving schemes to issue ZK Badges. You can see them here. While the contracts are still deployed, Sismo no longer maintains the ZK Badge protocol. Read more in this blog post.

Hydra Proof of Ownership

The Hydra-S1 proving scheme allows participants to establish, in one ZK proof, that for a given Proof Identifier:

  • They own 2 accounts (source and destination)

  • The source account is part of an Accounts Registry Tree

  • The source account was registered in the Accounts Registry Tree with a specific value

  • A claim about their source account value is true

    • e.g: "my account value is superior to 5" (non-strict claim)

    • or "my account value is strictly equal to 5" (strict claim)

  • They correctly generated a Proof Identifier

A Proof Identifier functions as a nullifier for the Hydra-S1 proving scheme, preventing the same user from minting a certain ZK Badge more than once.

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