ABDK Multisig Wallet

Copyright (c) 2017-2019, ABDK Consulting

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Overview

ABDK Multisig Wallet is an Ethereum smart contract that allows multiple (up to 255) parties to collectively own an Ethereum address. The owners may suggest transactions to be executed from wallet's address, approve suggested transactions, and execute transaction that collected enough approvals.

The smart contract is available in two versions: stand alone and delegated.

Stand alone version is more expansive to deploy, but slightly cheaper to use. Delegated version is about ten times cheaper to deploy than stand alone version, but more expensive to use and requires stand alone version to be already deployed on the same blockchain.

Features

Here is the list of high-level features offered by ABDK Multisig Wallet:

1. public and private transactions are both supported via single API;
2. it is possible to deploy smart contract from wallet's address via CREATE and CREATE2 opcodes;
3. data returned by executed transaction is captured and logged;
4. smart contract is available in two versions: stand alone (expensive deployment, cheaper use) and delegated (cheaper deployment, more expensive use).

Usage Scenarios

This section describes most common usage scenarios for ABDK Multisig Wallet.

1. Stand Alone Deployment

For stand alone deployment just deploy ABDKMultisigWallet smart contract from some of your addresses. This will create new stand alone ABDK Multisig Wallet. The address used for deployment will become the only owner of the wallet.

2. Delegated Deployment

For delegated deployment, deploy ABDKMultisigWalletDelegated providing address of some already deployed stand alone ABDK Multisig Wallet as constructor parameter. Make sure that this stand alone wallet is deployed in the same blockchain and is based on the same code version as new deployed delegated wallet.

3. Public Transaction

In order to execute public transaction, initiator needs to call suggestRevealAndApprove method providing transaction destination, ether amount, and binary data as parameters. Then other owners need to call approve method providing transaction ID as parameter. Transaction ID may be extracted from the events logged by suggestRevealAndApprove. Finally, when transaction collected enough approvals, one of the owners needs to call execute method providing transaction details as parameters. These details may also be extracted from the events logged by suggestRevealAndApprove. Optionally, the last approver may call approveAndExecute method instead ofapprove to save some gas.

4. Private Transaction

For private transaction, initiator calls suggestAndApprove method providing hash of transaction details. The hash may be calculated off-chain from transaction details via calcualteHash constant method. Then, initiator sends transaction details to other owners via e-mail or some other off-chain media. The owners use checkHash constant method to ensure that transaction details they receive from initiator actually match hash stored in the smart contract. Then owners call approve and finally execute the same way as for public transaction. For this flow, transaction details appear on-chain only when execute method is called.

5. Smart Contract Creation

In order to create smart contract from wallet's address, owners need to make wallet to execute a transaction that calls createSmartContract or createSmartContract2 method on the wallet itself. The former method gets as a parameter contract's byte code packed together with constructor arguments and creates smart contract using CREATE opcode. The latter method accepts salt parameter along with byte code, and uses CREATE2 opcode.

6. Change Number of Approvals Required

To change number of approvals required to execute a transaction, owners need to make wallet to execute a transaction that calls setApprovalsRequired method, providing new number of required approvals as a parameter. Note that is number of required approvals will ever be set higher than current number of owner, the wallet will be locked forever and there will be no way to execute any transaction from it anymore.

7. Change Owner

ABDK Multisig Wallet may have up to 255 owners. Wallet smart contract has 255 slots for owners with indexed by numbers 1..255. Indexes of the slots occupied by current owner do not have to go in sequence. I.e. there could be owners at slots #1 and #3, while slot #2 may be vacant.

In order to change the owner occupying certain slot, owners need to make wallet to execute a transaction that calls changeOwner method, providing slot index and new owner address as parameters. Providing zero owner address will effectively make slot vacant. Note that one owner may not occupy more than one slot, so providing an address of existing owner to changeOwner method will revert the transaction.

Transaction approvals made by owners are bound to slot indexes rather than to owner addresses, so new owner may revoke approvals made be the owner who previously occupied the same slot.

8. Cancel Transaction

In some cases owners may decide not to execute suggested transaction. This may happen if transaction was suggested by mistake, or became irrelevant while collecting approvals, or was submitted by malicious party using compromised owner's key. Such transaction may be cancelled by calling cancelSuggestion method and providing transaction ID as a parameter. This method should be called from wallet's address, so owners need to suggest, approve, and execute transaction that will call this method.

Functions and Properties

This section describes all public functions and properties of ABDK Multisig Wallet smart contract.

function suggest (bytes32 _hash)
public returns (uint256)

Suggest a transaction to be executed from the wallet's address. Parameter _hash is the hash of transaction details calculated via calculateHash method. Returns transaction ID. This method may be called only by wallet owners. Logs Suggestion event on successful invocation.

function reveal (uint256 _id, address _to, uint256 _value, bytes memory _data, uint256 _salt)
public

Reveal details of the transaction with given ID, revert in case provided transaction do not match hash stored in the smart contract. This method may be called only by wallet owners. Logs Revelation event on successful invocation.

function approve (uint256 _id)
public

Approve the transaction with given ID. This method may be called only be wallet owners. Logs Approval event on successful invocation.

function revokeApproval (uint256 _id)
public

Revoke approval from the transaction with given ID. This method may be called only be wallet owners. Logs ApprovalRevocation event on successful invocation.

function execute (uint256 _id, address _to, uint256 _value, bytes memory _data, uint256 _salt)
public returns (bool _status, bytes memory _returnedData)

Execute the transaction with given ID and transaction details, revert in case the transaction didn't collect enough approvals yet, or transaction details do not match hash stored in the smart contract. This method may be called only be wallet owners. Logs Execution event on successful invocation.

function createSmartContract (bytes memory _byteCode)
public payable returns (address _contractAddress, bytes memory _returnedData)

Create new smart contract using CREATE opcode. Parameter _byteCode is the byte code of the smart contract to be deployed packed together with constructor arguments. This method may only be called by the wallet itself via approved transaction. Logs ContractCreation event on successful invocation.

function createSmartContract2 (bytes memory _byteCode, bytes32 _salt)
public payable returns (address _contractAddress, bytes memory _returnedData)

Works similar to createSmartContract function but uses CREATE2 opcode with given salt.

function changeOwner (uint8 _ownerIndex, address _newOwner)
public

Change wallet owner at given index. This method may only be called by the wallet itself via approved transaction. Logs OwnerChange event on successful invocation.

function setApprovalsRequired (uint8 _approvalsRequired)
public

Change number of approvals required to execute a transaction. This method may only be called by the wallet itself via approved transaction. Logs ApprovalsRequiredChange event on successful invocation.

function cancelSuggestion (uint256 _id)
public

Cancel suggested transaction with given ID. This method may only be called by the wallet itself via approved transaction. Logs SuggestionCancellation event on successful invocation.

function calculateHash (address _to, uint256 _value, bytes memory _data, uint256 _salt)
public pure returns (bytes32)

Calculate transaction hash from destination address, ether amount, data, and salt.

function checkHash (uint256 _id, address _to, uint256 _value, bytes memory _data, uint256 _salt)
public view returns (bool)

Check, whether transaction details match hash stored in smart contract.

function approvalsCount (uint256 _id)
public view returns (uint8)

Get number of approvals required to execute a transaction.

function hashOf (uint256 _id)
public view returns (bytes32)

Get hash of transaction details stored in smart contract.

function isApproved (uint256 _id)
public view returns (bool)

Check, whether transaction with given ID collected enough approvals to be executed.

function isApprovedBy (uint256 _id, address _owner)
public view returns (bool)

Tell, whether transaction with given ID is approved by given owner.

function getOwnerAt (uint8 _index)
public view returns (address)

Get address of the owner at given index. Return zero address in case owner slot with given index is currently vacant.

function suggestAndReveal (address _to, uint256 _value, bytes memory _data)
public returns (uint256)

Convenient and gas effective way to suggest and reveal a transaction.

function suggestRevealAndApprove (address _to, uint256 _value, bytes memory _data)
public returns (uint256)

Convenient and gas effective way to suggest, reveal, and approve a transaction.

function suggestAndApprove (bytes32 _hash)
public returns (uint256)

Convenient and gas effective way to suggest and approve a transaction.

function suggestApproveAndExecute (address _to, uint256 _value, bytes memory _data)
public returns (bool _status, bytes memory _returnedData)

Convenient and gas effective way to suggest, approve, and execute a transaction. Use this method when number of required approvals is less than or equals to one.

function approveAndExecute (uint256 _id, address _to, uint256 _value, bytes memory _data, uint256 _salt)
public returns (bool _status, bytes memory _returnedData)

Convenient and gas effective way to approve and execute a transaction.

uint8 public ownersCount

Current number of owners.

uint8 public approvalsRequired

Number of approvals required to execute a transaction.

Events

This section describes all events that ABDK Multisig Wallet smart contract may log.

event Deposit (
  address indexed from,
  uint256 value,
  bytes data)

Logged by fallback function on incoming transactions.

event Suggestion (
  uint256 indexed id,
  address indexed owner,
  bytes32 indexed hash)

Logged when new transaction is suggested.

event Revelation (
  uint256 indexed id,
  address indexed owner,
  address indexed to,
  uint256 value,
  bytes data,
  uint256 salt)

Logged when transaction details are revealed.

event Approval (
  uint256 indexed id,
  address indexed owner)

Logged when transaction is approved by wallet owner.

event ApprovalRevocation (
  uint256 indexed id,
  address indexed owner)

Logged when wallet owner revokes transaction approval.

event Execution (
  uint256 indexed id,
  address indexed owner,
  bool status,
  bytes returnedData)

Logged when transaction has been executed.

event SmartContractCreation (
  address indexed contractAddress,
  bytes returnedData)

Logged when smart contract has been created.

event OwnerChange (
  uint8 indexed ownerIndex,
  address indexed oldOwner,
  address indexed newOwner)

Logged when owner has been changed.

event ApprovalsRequiredChange (
  uint8 newApprovalsRequired)

Logged when number of approvals required to execute a transaction has been changed.

event SuggestionCancellation (
  uint256 indexed id)

Logged when suggested transaction has been cancelled.