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Circuit Model

The Zero-Knowledge circuit is the mathematical core that enforces the rules of verification without revealing secrets.

Circuit Layer

Concept​

Deeproof uses a circuit written in Circom. The circuit's job is to answer the question:

"Does this user know a valid UserID and Trapdoor that hash to this Commitment, and is their KYC level sufficient?"

...without revealing the UserID or the Trapdoor.

Inputs​

The circuit takes two types of inputs:

1. Private Inputs (Secret)​

These values are known only to the user (prover) inside their browser. They are never revealed to the public or the contract.

  • userId: The unique identifier from the identity provider (e.g., Binance User ID).
  • trapdoor: A random secret number generated by the user's extension. This acts as a password.
  • userKycLevel: The actual KYC level retrieved from the provider.

2. Public Inputs (Visible)​

These values are public and used by the smart contract to verify the proof.

  • minKycLevel: The minimum required KYC level (e.g., "2").
  • identityCommitment: The resulting hash of the UserID and Trapdoor.

logic​

The circuit performs the following checks:

  1. KYC Check: It asserts that userKycLevel matches (or is greater than) minKycLevel.
    • Logic: userKycLevel === minKycLevel constraint.
  2. Commitment Generation: It hashes the userId and trapdoor using the detailed Poseidon Hash algorithm.
    • Logic: commitment = Poseidon(userId, trapdoor)

Output​

The circuit outputs:

  • The Proof: A cryptographic string proving the constraints are met.
  • The Commitment: A public hash that represents the user's identity identity (like a fingerprint) but cannot be reversed to find the original ID.