---
# System prepended metadata

title: 'BEP-???: Cross Chain Relayer Management'

---

# BEP-???: Cross Chain Relayer Management

## 1. Summary

This BEP introduces a new governance proposal type to manage the set of whitelisted Relayers.  A Relayer whitelist was introduced recently to the BSC genesis contracts ([PR-198](https://github.com/bnb-chain/bsc-genesis-contract/pull/198)). This BEP will improve the management of the relayer whitelist by introducing Relayer Managers, where a Relayer Manager can manage the registration of a single Relayer. Managers will be elected and ejected via governance.

## 2. Abstract

This BEP introduces a new governance proposal type to manage Relayer Manager public keys that will be stored in the [`RelayerHub`](https://github.com/bnb-chain/bsc-genesis-contract/blob/71dcd4c409a68a6e084645a9f1f80adecd5a4269/contracts/RelayerHub.sol) genesis contract on BSC.  

Relayer Managers will be able to manage their individual elayer public key.  Only Relayer public keys registered via Managers will be able to invoke the `RelayerHub` smart contract for cross chain transfers.  


## 3. Status

This BEP is a draft.

## 4. Motivation

After the [BSC Bridge exploitation](https://github.com/verichains/public-audit-reports/discussions/17) it is important we introduce some mechanism in place that enhances the security of the system. A governance based set Manager public keys who manage a single Relayer adds an extra layer of security.


## 5. Specification


### 5.1 Current Relayer Whitelist

Currently whitelisted relayers are [hardcoded](https://github.com/bnb-chain/bsc-genesis-contract/blob/a8476b2aefba0a66db86311ab44d43d7e2df24fe/contracts/System.sol#L88) in the `System` genesis smart contract.  This list needs to be updated manually by deploying a new version of the smart contract.

### 5.2 The New Whitelisting Mechanism
After the implementation of this BEP:

- A Relayer Manager role will be introduced with corresponding public keys.   
- The set of Managers will be updated via governance using the existing [param change proposal](https://github.com/bnb-chain/bnb-chain.github.io/blob/master/docs/learn/bsc-gov-workflow.md#submit-cross-chain-param-change-proposal) mechanism.
- Managers will have to register the 100BNB once their public key has been added to the set of Managers via governance
- Once registered, Managers will be able to add an associated Relayer public key
- There will be a 1:1 relationship between Manager public key to active Relayer public key.
- Only associated Relayers can send cross chain messages. 
- Managers can modify public key of their Relayer at any time.  This will facilitate rotation of Relayer instances.

### 5.3 `RelayerHub` Smart Contract Changes
#### Relayer Manager functions
```
function removeManagerByGov(address) external onlyGov
```
Removes Manager public key from current set of Managers. 100BNB will be returned to Manager address if the Manager has desposited.  Emits an event on success. This is only called via governance.
```
function removeManager() external onlyManager
```
Removes Manager public key from current set of Managers. 100BNB will be returned to Manager address if the Manager has desposited. Emits an event on success.
```
fuction addManagerByGov(address) external onlyGov
```
Adds a Manager public key to the current set of Managers. This is only called via governance. Emits an event on success.

```
function registerManager() external payable onlyManager
```
Registers an Manager and accepts 100BNB fee. Emits an event on success.

```
function addRelayer(address) external onlyManager
```
Adds a Relayer for the calling Manager.  Overwrites Relayer if there is an existing Relayer already added. Emits an event on success.

```
function registerManagerAddRelayer(address) external payable onlyManager
```
Calls both `registerManager` and `addRelayer`.

```
function removeRelayer() external onlyManager
```
Removes a Relayer associated to the calling Manager.  Emits an event on successful removal.

#### Relayer functions
```
function isRelayer(address) external bool
```
This will be called by the Relayer codebase, instead of registering.  Relayer can stop if this returns false


#### `updateParam` Changes

```
  function updateParam(string calldata key, bytes calldata value) external override onlyInit onlyGov{
    if (Memory.compareStrings(key,"requiredDeposit")) {
      ...
    } else if (Memory.compareStrings(key,"dues")) {
      ...
    } else if (Memory.compareStrings(key,"addManager")) {
       // TODO check and parse value
       // addManagerAddress(...)
    } else if (Memory.compareStrings(key,"removeManager")) {
       // TODO check and parse value
       // removeManagerAddress(...)
    } else {
      require(false, "unknown param");
    }
    emit paramChange(key, value);
  }
```
The `updateParam` function will be modified accept two new keys
- `addManager` to add a Manager to the stored Manager set.
- `removeManager` to remove a Manager from the stored Manager set.

#### Functions to be Deprecated

These Relayer functions will be deprecated:
```
function register() external payable ...
function unregister() external ...
```

### 5.4 Relayer Changes

Update Relayer codebase to no longer register and deposit. Update abi? and run code generation to call new `verifyRelayer` method on `RelayerHub` smart contract and proceed to relay cross chain messages on success.

### 5.5 Existing relayer key migration

Manager keys will need to be supplied for the existing two relayers.  Manger set will be seeded with these two Manager public keys.  Relayer public keys will be registered to these Managers.

Existing Relayers will need to pull down relayer code once the `RelayerHub` SC has been upgraded.

### 5.6 CLI commands
```
## mainet
./bnbcli params  submit-bscParam-change-proposal  --key "addManager" --value "ADDRESS"   --target 0x0000000000000000000000000000000000001006 --deposit 200000000000:BNB     --voting-period 100   --side-chain-id  bsc  --title "add new super trusty relayer"  --from alice  --trust-node   --chain-id Binance-Chain-Tigris

## testnet
./tbnbcli params  submit-bscParam-change-proposal  --key "addManager" --value "ADDRESS"   --target 0x0000000000000000000000000000000000001006 --deposit 200000000000:BNB     --voting-period 100   --side-chain-id  chapel  --title "add new super trusty relayer"  --from alice  --trust-node   --chain-id Binance-Chain-Ganges
```
The commands used to create a change proposal to governance.

#### Payload Structure

TODO: `addManager` and `removeManager` cases

## 6. Workflow

TODO: add workflow diagrams

## 7. License

The content is licensed under [CC0](https://creativecommons.org/publicdomain/zero/1.0/).

## Open Questions

- How do we deploy this thing?