Current Validators: How to Add a New Bridge Validator

Instructions for current bridge validators who are adding an additional validator to the set.

After a ballot is finalized, the new validator is added to the bridge management multisignature wallets (one on each side of the bridge).

The submitter will execute these methods: addValidator and (optionally) setRequiredSignatures method. After encoding the data for each of these methods, it is sent to each contract (one on either side of the bridge) using the submitTransaction execution method.

Multisignature wallet addresses (for reference):

• ETH Mainnet: 0xff1a8EDA5eAcdB6aAf729905492bdc6376DBe2dd

• xDai chain: 0x0d3726e5a9f37234d6b55216fc971d30f150a60f

Before starting, current validators should determine (through Slack or other means):

1) who will add the new validator (the submitter)

2) coordinate a time when the other validators will confirm the transaction, as the bridge will be stopped to complete the upgrade.

3) Ask the POA team to add a new bridge validator to the Certifier contract and confirm it has been added. This enables the node to relay bridge transactions with zero gas price.

Steps to add a new bridge validator

1) Use the addValidator method from the BridgeValidators ABI and the new validator account to encode the data for the transaction. This can be accomplished in different ways, this example uses https://abi.hashex.org/

• Scroll down to enter the parameters manually

• 1. Select ‘your function’ for function type and add addValidator function

• 2. Select address for Argument, paste in the new bridge validator’s address

• 3. Copy the example output. It should have a similar format to: 4d238c8e0000000000000000000000000d3726e5a9f37234d6b55216fc971d30f150a60f

Add in parameters manually and copy ABI

2) Use Nifty Wallet (or another tool that can build transactions based on contract source code/ABI) to invoke the submitTransaction method of the multisig wallet contract. You will do this for the ETH Mainnet and the xDAI chain. The following example uses Nifty Wallet.

SubmitTransaction

2.1 ETH Mainnet

• a. Open Nifty Wallet, make sure you are on the Eth Mainnet, and select the ETH Mainnet contract account 0xff1a8EDA5eAcdB6aAf729905492bdc6376DBe2dd. (Import Account -> Contract account -> Paste in Address). For additional instructions see https://medium.com/poa-network/nifty-wallet-now-supports-interactions-with-smart-contracts-5e8c43c19e3a

• b. Click Execute Methods, and choose the submitTransaction method

• c. Destination address is 0xe1579dEbdD2DF16Ebdb9db8694391fa74EeA201E

• d. Value is 0

• e. Data is the bytecode generated in 2d. Add 0x before the value. In our example it is 0x4d238……..

• f. Click Next

Enter parameters in Nifty wallet

• g. Choose the contract to execute this transaction. Select your Bridge Validator account and click Next.

• h. You should see a transaction confirmation popup to complete the process. Once the transaction is complete, identify the index of the transaction returned in the Submission event and make a note of it.

2.2 xDAI Chain

• a. Open Nifty Wallet, switch to the xDai network and go to xDai contract account 0x0d3726e5a9f37234d6b55216fc971d30f150a60f. If you have not used this feature before and need to import the contract, see https://medium.com/poa-network/nifty-wallet-now-supports-interactions-with-smart-contracts-5e8c43c19e3a

• b. Click Execute Methods, and choose the submitTransaction method

• c. Destination address is 0xb289f0e6fbdff8eee340498a56e1787b303f1b6d

• d. Value is 0

• e. Data is the bytecode generated in 2d. Add 0x before the value. In our example, it is 0x4d238……..

• f. Click Next

• g. Choose the contract to execute this transaction. Select your Bridge Validator address.

• h. Once this is complete, identify the index of the transaction returned in the Submission event and make a note of it.

setRequiredSignatures

3) Use the setRequiredSignatures method from the BridgeValidators ABI and the new validator account to encode the data for the transaction. This can be accomplished in different ways, this example uses https://abi.hashex.org/

• a. Scroll down to enter the parameters manually

  • b. Select ‘your function’ for function type and add setRequiredSignatures function

  • c. Select Uint256 for Argument, paste in the number of required signatures to account for the new validator. This number should be at least a majority of validators, the current set of validators decides this number.

  • d. Example output should have a similar format aec452390000000000000000000000000000000000000000000000000000000000000005

4) Complete steps as in #3, using the new ABI value with the submitTransaction method to send this transaction to both the ETH Mainnet and the xDai chain.

5) Share Submission event indexes for all transactions with current validators through the Slack channel or another means.

Chain	Contract	Method	Index
ETH	0xff1a8...Be2dd	addValidator	3
ETH	0xff1a8...Be2dd	setRequiredSignatures	5
xDai	0x0d...a60f	addValidator	2
xDai	0x0d...a60f	setRequiredSignatures	4

6) The current validators must then confirm these transactions on both sides of the bridge. Nifty Wallet (or another tool) may be used to confirm the transactions.

All bridges must be stopped before the last required validator submits a signature, then restart after it is submitted,* as this signature changes the value stored in the bridge contract. Validators need to coordinate here in order to stop and restart the bridge contracts.

• a. Stop bridge instance sudo service poabridge stop

• b . Open Nifty Wallet, make sure you are on the Eth Mainnet, and select the ETH Mainnet contract account 0xff1a8EDA5eAcdB6aAf729905492bdc6376DBe2dd

• c. Click Send, and choose the confirmTransaction method

• d. Select Index as transaction ID

• e. Choose your Bridge Validator address to execute the transaction

• f. Set the gas limit two times larger than the gas estimator suggests. As soon as enough confirmations are received, the method is invoked automatically.

• g. Repeat for the second method - ie setRequiredSignature

• h. Switch to the xDai network and select the xDai contract account 0x0d3726e5a9f37234d6b55216fc971d30f150a60f

• i. Repeat steps b-f to confirm transactions on the xDai chain.

7) Restart the bridge after the last validator signature is submitted. sudo service poabridge start

The new validator should now be added

Additional Details

• For more details regarding bridge contracts management, see https://forum.poa.network/t/xdai-bridge-contracts-management/1777

• For more information on Nifty wallet smart contract interaction, see https://forum.poa.network/t/nifty-wallet-now-supports-interactions-with-smart-contracts/1906