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ZK Identity System

The ZK Identity System provides a privacy-preserving way to attest to an identity (e.g., verifying you are a Github user) without revealing the specific identity or linking multiple actions to the same user. It uses Zero-Knowledge Proofs (ZK-SNARKs) to guarantee:
  1. Privacy: No one knows which user performed an action.
  2. Uniqueness: A user cannot double-spend an action in the same context (via Nullifiers).
  3. Soundness: Mathematical proof of validity.

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Core Concepts

Commitment

Poseidon(provider_id, secret) A cryptographic commitment to an identity, stored on-chain in a Merkle Tree. It hides the user’s ID and secret.

Nullifier

Poseidon(provider_id, secret, context) A unique hash generated for a specific action (context). Including secret ensures nullifiers cannot be linked across contexts even if provider_id leaks. Prevents double-spending while maintaining cross-context unlinkability.

Merkle Tree

A valid commitment must exist in the global Merkle Tree. The ZK proof verifies inclusion in this tree.

ZK Proof

A Groth16 proof that asserts: “I know a secret corresponding to a commitment in the Merkle Tree, and here is my unique nullifier for this context.”

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Architecture Overview

The system operates in a Two-Phase Flow:
1

Generate Secret

User generates a random secret locally. This never leaves their device.
2

Create Commitment

User calculates commitment: Hash(provider_id, secret).
3

Submit to Chain

User submits the commitment to the blockchain via an identity_commitment transaction.
4

Merkle Update

Validators verify the transaction and add the commitment to the global Merkle Tree.

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Phase 2: Prove Ownership (Repeatable)

When a user wants to perform an action (e.g., vote, claim airdrop) anonymously:
1

Generate Proof

User uses their secret and the current Merkle path to generate a ZK proof locally.
2

Calculate Nullifier

User calculates a nullifier based on the action context: Hash(provider_id, secret, context).
3

Submit Attestation

User submits identity_attestation transaction with the proof and nullifier.
4

Verification

Validators verify the proof against the current Merkle root and checking if the nullifier has been used before.

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Privacy Model

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Security Guarantees

  • Anonymity Set: All users across all providers in the Merkle Tree.
  • Unlinkability: No link between the commitment (Phase 1) and the attestation (Phase 2).
  • Double-Spend Protection: The nullifier guarantees a user can only act once per context.