pir-client

Private Information Retrieval client for vote-nullifier-pir. Fetches circuit-ready Merkle non-membership proofs for Zcash nullifiers without revealing which nullifier is being queried to the server.

Used by Zcash wallets integrating shielded voting: before building a delegation ZKP, a wallet must prove its notes' nullifiers are absent from the on-chain nullifier set. The set has tens of millions of entries and can't be downloaded in full; pir-client performs a two-tier YPIR query that returns only a short authentication path.

Usage

use std::sync::Arc;

use pir_client::{ImtProofData, PirClientBlocking, Transport};

let transport: Arc<dyn Transport> = Arc::new(my_http_transport);
let client = PirClientBlocking::with_transport("https://pir1.example.com", transport)?;
let proof: ImtProofData = client.fetch_proof(my_nullifier)?;
assert!(proof.verify(my_nullifier));

Async equivalent:

use std::sync::Arc;

use pir_client::{PirClient, Transport};

let transport: Arc<dyn Transport> = Arc::new(my_http_transport);
let client = PirClient::with_transport("https://pir1.example.com", transport).await?;
let proofs = client.fetch_proofs(&[nf1, nf2, nf3]).await?;

The returned ImtProofData { root, nf_bounds, leaf_pos, path: [Fp; 29] } is then fed as a witness into the Zcash-voting delegation ZKP.

Security

• The client always sends the Tier 2 query even after a Tier 1 failure, to prevent a malicious server from distinguishing queries via timing.
• Verify each proof locally with proof.verify(nullifier) before trusting the returned root.

License

Dual-licensed under MIT or Apache-2.0. See LICENSE-MIT and LICENSE-APACHE.