ZK-Donation

This project addresses the "transparency vs. privacy" dilemma in humanitarian aid. While public blockchains provide auditability for donations, they expose vulnerable beneficiaries to social stigma and physical danger by making their transaction history public.

We have built a privacy-preserving protocol for Purpose Bound Money (PBM) that shields recipient data from the public while maintaining accountability. By utilizing Zero-Knowledge Proofs (ZKP), we ensure that transaction details (amount, merchant, and timing) remain confidential to third parties. However, we introduce a "Mandatory Auditability" feature: the protocol cryptographically enforces the delegation of a viewing key to the original donor. This creates a dual-access model where the recipient has the spending authority, but the donor retains the right to verify that the funds were used for their intended purpose. This balances the donor's need for trust with the beneficiary's right to safety.

The core of this project is a confidential transfer circuit implemented using the Noir DSL. We chose Noir for its ability to generate efficient ACIR (Abstract Circuit Intermediate Representation), allowing us to handle complex logic like private state transitions and encrypted log broadcasting seamlessly.

The Tech Stack:

Noir: To write the ZKP circuits that verify transaction validity without revealing inputs.

Dual-Key Encryption: We implemented a scheme where each transaction "note" is encrypted for two parties: the recipient (for spending) and the donor (for viewing). The circuit enforces that the donor’s public key is correctly included in the encryption process, making auditability non-optional.

Smart Contracts: Deployed on an EVM-compatible layer (likely Aztec or a ZK-Rollup), managing the PBM lifecycle—minting, confidential transfer, and merchant redemption.

The "Hacky" Bit: > One notable challenge was ensuring the donor's viewing rights persist through multiple hops of funds. We implemented a "provenance-carrying" encrypted state where the donor's identifier is cryptographically linked to the PBM's metadata. This ensures that even if the money is split or merged within the private state, the original donor's audit bridge remains intact without leaking who that donor is to the public.