The Gnosis Safe is a multisignature wallet with support for confirmations using signed messages based on ERC191. It is the successor of the Gnosis Multisig Wallet and combines more functionality with reduced gas costs. The Gnosis Safe allows basic wallet configuration like adding and removing owners and more advanced features like extensions, which allow to do transactions with different requirements.
A Safe transaction has the same parameters as a regular Ethereum transaction: A destination address, an Ether value and a data payload as a bytes array. In addition, Safe transactions have two more parameters: operation and nonce.
The operation type specifies if the transaction is executed as a CALL, DELEGATECALL or CREATE operation. While most wallet contracts only support CALL operations, adding DELEGATECALL operations allows to enhance the functionality of the wallet without updating the wallet code. As a DELEGATCALL is executed in the context of the wallet contract, it can potentially mutate the state of the wallet (like changing owners) and therefore can only be used with known, trusted contracts. The CREATE operation allows to create new contracts with bytecode sent from the wallet itself.
The nonce prevents replay attacks and is increased with every successfully executed Safe transaction. The number of executed Safe transactions is therefore equal to the current nonce saved in the wallet storage.
As the creation of new contracts is a very gas consuming operation, Safe contracts use a proxy pattern where only one master copy of a contract is deployed once and all its copies are deployed as minimal proxy contracts pointing to the master copy contract. This pattern also allows to update the contract functionality later on by updating the address of the master copy in the proxy contract. As contract constructors can only be executed once at the time the master copy is deployed, constructor logic has to be moved into an additional persistent setup function, which can be called to setup all copies of the master copy. This setup function has to be implemented in a way it can only be executed once. It is important to note that the master copy contract has to be persistent and there should be no possibility to execute a selfdestruct call on the master copy contract.
The proxy contract implements only two functions: The constructor setting the address of the master copy and the fallback function forwarding all transactions sent to the proxy via a DELEGATECALL to the master copy and returning all data returned by the DELEGATECALL.
The proxy factory allows to create new proxy contracts pointing to a master copy and executing a function in the newly deployed proxy in one transaction. This additional transaction can for example execute the setup function to initialize the state of the contract.
The Gnosis Safe contract implements all basic multisignature functionality. It allows to execute Safe transactions and Safe extensions.
Safe transactions can be used to configure the wallet like managing owners, updating the master copy address or whitelisting of extensions. All configuration functions can only be called via transactions sent from the Safe itself. This assures that configuration changes require owner confirmations.
Before a Safe transaction can be executed, the transaction has to be confirmed by the required number of owners. There are two ways to confirm transactions:
- Owners represented by private key controlled accounts can sign the transaction hash.
- Owners represented by contract accounts (e.g. other Safe contracts) or private key controlled accounts can confirm a transaction by calling the
confirmTransactionfunction.
Once the required number of confirmations is available executeTransaction can be called by sending confirmation signatures and references to confirmations sent using confirmTransaction. In case the account calling executeTransaction is a wallet owner its call can be used as confirmation and the owner doesn't have to confirm with a signed message or confirmTransaction.
executeTransaction expects all confirmations sorted by owner address. This is required to easily validate no confirmation duplicates exist.
Assuming we have 4 owners in a 4 out of 4 multisig configuration:
0x1(Private key)0x2(Private key)0x3(Safe contract)0x4(Private key)
0x1 and 0x2 are confirming by signing a message. 0x3 is confirming by sending a confirmTransaction transaction. 0x4 is calling the executeTransaction function and therefore also confirming the transaction.
The Safe transaction parameters used for executeTransaction have to be set like the following:
v = [v_0x1, v_0x2]r = [r_0x1, r_0x2]s = [s_0x1, s_0x2]owners = [0x3, 0x4]indices = [2, 3]
v, r and s are the signature parameters for the signed confirmation messages. Position 0 in v represents 0x1's signature part and corresponds to position 0 in r and s. The owners array contains owner addresses confirming transaction by sending a confirmTransaction or calling executeTransaction. Their address position in the sorted array of all confirming owner addresses is set in the indices array starting from position 0:
allConfirmingOwners = [0x1, 0x2, 0x3, 0x4]
Position of 0x3 is 2 and position of 0x4 is 3 in indices array.
Extensions allow to execute transactions from the Safe without the requirement of multiple signatures. Extensions define their own requirements for execution. Every extension has to implement the interface for extensions. This interface requires only one function isExecutable receiving all transaction parameters and evaluating if a transaction is allowed to be executed. Extension transactions don't require a nonce as they don't require replay protection.
The Daily Limit Extensions allows an owner to withdraw specified amounts of specified ERC20 tokens on a daily basis without confirmation by other owners. The daily limit is reset at midnight UTC. Ether is represented with the token address 0. Daily limits can be set via Safe transactions.
The Social Recovery Extensions allows to recover a Safe in case access to owner accounts was lost. This is done by defining a minimum of 3 friends’ addresses as trusted parties. If all required friends confirm that a Safe owner should be replaced with another address, the Safe owner is replaced and access to the Safe can be restored. Every owner address can be replaced only once.
The Whitelist Extensions allows an owner to execute arbitrary transactions to specific addresses without confirmation by other owners. The whitelist can be maintained via Safe transactions.
Libraries can be called from the Safe via a DELEGATECALL. They should not implement their own storage as this storage won’t be accessible via a DELEGATECALL.
This library allows to batch transactions and execute them at once. This is useful if user interactions require more than one transaction for one UI interaction like approving an amount of ERC20 tokens and calling a contract consuming those tokens. If one transaction fails all are reverted.
This library allows to create a new Safe extension and whitelist this extension for the Safe in one single transaction.
npm installtruffle testtruffle deployAll contracts are WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
All smart contracts are released under GPL v.3.
- Stefan George (Georgi87)
- Christian Lundkvist (christianlundkvist)
- Nick Dodson (SilentCicero)
- Gonçalo Sá (GNSPS)
- Richard Meissner (rmeissner)
The code has not been reviewed yet.