Relayer

Relayers submit transactions on your behalf. Most users interact via relayer for all operations.

Why Relayers?

1. No ETH needed - Users don't need gas tokens
2. Privacy - Your EVM address isn't the msg.sender
3. UX - Single flow regardless of operation type

User creates proof/signature locally
    │
    ▼
Sends to relayer (off-chain)
    │
    ▼
Relayer submits tx
    │
    ▼
Contract verifies proof (not msg.sender)

Authorization Model

Operation	Authorization	How It Works
Register BPK	EIP-712 signature	User signs typed data, relayer submits
Shield	EIP-2612 permit	User signs permit, relayer pulls tokens
Transfer	ZK proof	Proof proves BPK ownership — no signature needed
Unshield	ZK proof	Proof proves BPK ownership — no signature needed

Key insight: For transfer and unshield, the ZK proof IS the authorization. The contract verifies the proof, not msg.sender. This means any relayer can submit the transaction without any trust.

SDK Usage

The SDK handles relayer interaction transparently — just pass useRelayer: true:

const client = await createClient({
  chainId: 8453,
  relayerUrl: 'https://eb-relayer.zkprivacy.dev',
});

const wallet = client.wallet({ spendingKey: keys.spendingKey, account });

await wallet.USD.registerBPK();

await wallet.USD.shield({ amount: 100_000000n, useRelayer: true });

await wallet.USD.transfer({
  to: 'zk1qyp5xs...',
  amount: 50_000000n,
  useRelayer: true,
});

await wallet.USD.unshield(50_000000n, undefined, { useRelayer: true });

The SDK generates the proof or signature locally, sends it to the relayer, and the relayer submits the transaction on-chain. The user never pays gas.

What Relayer Learns

Information	Relayer Knows?
That you're submitting a tx	Yes
Timing of submission	Yes
Transfer amount	No (encrypted)
Your identity	No (if using Tor)