How to become a relayer?

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Following the execution of Tornado Cash 10th governance proposal, anyone can become a relayer for Tornado Cash users.
The only condition to be included on the Tornado Cash UI is to lock a min. of 300 TORN*. To remain listed, it is needed to keep enough TORN locked (~40 TORN at the moment in April 2022) to be able to pay back the transaction fee to the staking contract.
*This minimum stake can be changed by a governance vote at any time.
Relayers form an essential & necessary part of the Tornado Cash ecosystem. Their use guarantees privacy as they solve the infamous “fee payment dilemma” : how to pay fees for token withdrawals from a pool while maintaining anonymity?
Therefore, relayers act as third parties and manage the entire withdrawal. They pay for transaction fees by deducting them directly from the transferred amount. They also charge an additional fee for their services.
Since the implementation of the Relayer Registry proposal, the protocol collects a fee directly from the relayer’s staked balance through the StakingReward contract for each withdrawal. This fee percentage may vary from one pool to another and is also subject to change through on-chain governance.
Currently, it is fixed at 0.3% . Some pools remain without fees, either because the instance is too small to assign a fee (0.1 ETH, 100 DAI/USDT, 1000 DAI/USDT), or because there is not enough liquidity on Uni v3 (all cDAI instances).
How to Become a Relayer?
Anyone can become a relayer for the protocol in 6 simple steps through a Relayer Registry User Interface (UI).
Below you will find everything your need to join our relayers' club & get listed on Tornado Cash decentralized relayer registry.
1. Warning: Understand & Accept Potential Risks
Before you commit to sharing part of your journey with Tornado Cash users as a relayer, you need to understand & accept all potential risks of being a relayer for the protocol.
How a Relayer is chosen by user interface
The formula for designating a relayer is as follows:
The list of all registered relayers is retrieved from the Relayer Registry smart contract.
For each relayer, calculate a score based on its staked TORN and its fee. The higher the stake, the higher the score is; the higher the fee, the lower the score is. For Ethereum mainnet, the formula used to calculate the score is stake * [1 - 25*(fee-0.33)^2]; for sidechains, the formula is stake * [1 - 11.89*(fee-0.01)^2].
Then randomly pick a relayer, weighted by its calculated score.
2. Set up Relayer
The first concrete step is to run the Tornado Cash Relayer software for Ethereum Mainnet on your computer. All steps are outlined in the protocol's github. To complete this task successfully, you will have to carefully follow these instructions.
GitHub - tornadocash/tornado-relayer: Relayer for Tornado cash.
GitHub
Once completed, you will need to insert your url in the input box.
It is strongly recommended that you use your own RPC nodes. Instructions on how to run full nodes can be found here.
3. Set Up ENS Subdomain
The next steps entail:
Creating an ENS domain for your relayer.
Setting up its mainnet subdomain.
Adding a TXT record with the Relayer URL to the mainnet subdomain according to this specific format:
Ethereum Relayers (Mandatory)
TXT record
mainnet-tornado.xxx.eth
goerli-tornado.xxx.eth
Sidechains Relayers (Optional)
You also have the option to add subdomains with their corresponding TXT records to support chains other than Ethereum. Sidechains relayers use a different version of the Relayer software. The complete requirements with instructions are found here.
TXT record
bsc-tornado.xxx.eth
gnosis-tornado.xxx.eth
polygon-tornado.xxx.eth
optimism-tornado.xxx.eth
arbitrum-tornado.xxx.eth
avalanche-tornado.xxx.eth
Nova Relayer (Optional)
Tornado Cash Nova uses its own version of the software. If you wish to become a relayer for Tornado Cash Nova, you will find instructions to follow here.
TXT record
gnosis-nova.xxx.eth
4. Set Up Workers
Workers are the addresses that will allow your relayer to send ZK-proofs to users. By default, the first worker is the ENS domain owner's address.
To ensure an extra level of security, we advise you to set up more than one worker.
Only the mainnet requires you to register workers. All other networks do not require the use of registered workers.
5. Stake
With the implementation of a decentralized relayer registry, a staking condition has been introduced as a requirement to become listed on Tornado Cash UI. Keep in mind staking TORN is now necessary to be added to the recommended list of relayers.
The minimum staked amount is currently set by Tornado Cash governance at 300 TORN. This threshold can be changed by Tornado Cash governance at any time.
When a relayer is used in the Tornado Cash pool, a small amount of TORN is automatically collected from this staked balance by the StakingReward contract. This element is essential to keep in mind as relayers will need to keep enough TORN locked (~40 TORN at the moment in April 2022) to be able to pay back the transaction fee to the staking contract.
The collected fees are subsequently distributed among DAO members with locked TORN tokens. TORN are usually locked to participate in on-chain governance (submitting & voting on proposals). You can find more information both on this forum post & in the Staking TORN documentation page.
Your staked TORN amount is not claimable, and it is non-refundable.
6. Summary: Final Verification & Registration
Last but not least, we advise you to double-check all information displayed in the Summary before registering.
Welcome to the relayer team! Thanks to you, privacy can be better respected 💚
Written by @bt11ba & @ayefda​