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Smart Contract for Dapper
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README.md

Dapper-Contracts

Overview

This repository implements the Dapper Ethereum smart contract wallet. The wallet has recovery and multi-signature capabilities (via cosigner address) as well as allowing for users to have full sovereignty over all features.

Audit of Dapper

To view the audit of Dapper's smart contracts please see Sigma Prime's audit here and blog post describing the audit here.

Dev Setup

Requirements

Node 9

Run Tests

  • npm install
  • npm run build
  • due to contract bytecode being dependent upon the path at which it was compiled, copy the bytecode from FullWallet.json into WalletFactory.sol
  • npm test

Definitions

key - Unless otherwise noted, a key is defined as an Ethereum compatible public/private key pair, used with Ethereum Accounts. When in the context of smart contracts, key refers to an Ethereum address.

transaction - Unless otherwise noted, a transaction is defined as an Ethereum transaction.

value transfer - the transferring of value by way of ETH, ERC20, ERC721, or any 3rd party contract call.

Wallet Design and Features

In contrast to the standard HD wallet implementation, rather than an externally owned account, all assets (ETH, ERC20, ERC721, etc.) for the user are associated with the wallet's public address (contract account) for which by construction there exists no private key; hence value transfer actions from the wallet to another address require function calls to be performed on the wallet itself. For importing assets, one simply sends them to the user wallet contract address.

Recovery Key

The recovery key is an ephemeral key that exists only in memory on the clients device for a brief moment. The key is generated and used to sign the recovery transaction and then erased from memory. The wallet contract keeps track of the public address of the recovery key that signed the recovery transaction.

Recovery Transaction

The recovery transaction is a transaction signed by the recovery key. This transaction authorizes the RECOVERY operation. The RECOVERY operation is defined as the one time atomic removal of all existing device keys and the assignment of the backup key as the sole device key.

It should be noted that the recovery transaction in and of itself is of no use to anyone without the corresponding backup key.

Backup Key

The backup key is a key that is used in conjunction with the recovery transaction in order to perform a RECOVERY.

It should be noted that the backup key in and of itself is of no use to anyone without the corresponding recovery transaction.

In the Dapper client interface, the backup key is stored in the users "Recovery Kit" in mini private key format.

Device Keys

Administration and use of the wallet is controlled by what we refer to as device keys. More than one device key can exist. A device key needn't be the "creator" or "owner" of the wallet contract.

It is of note that a device key can also be a smart contract, which provides a way to provide additional functionality; for example: a dead man switch or enforcement of a daily ETH limit.

It is recommended that the number of device keys is kept to a minimum to increase security and reduce attack surface

As these keys allow unrestrained value transfer from the wallet, it is highly recommended that device keys have a cosigner set to improve security and reduce risk and a multiple single points of failure scenario

Device Key Capabilities

  • Perform value transfer transactions
  • Add another device key
  • Remove another device key
  • Adjust the cosigner on a device key
  • Rotate the backup key and recovery transaction

Device Key Inabilities

  • Perform a RECOVERY operation; this is restricted to the recovery key only.

Device Key Properties

An device key's only property is an optional cosigner address

Cosigner Address

Any device key can sign the outer transaction that allows you to perform value transactions, etc. However, a cosigner address can be set per device key such that a second signature must be provided in addition to the one provided by the device key.

This design allows for on-chain (smart contract) or off-chain checks (ie. fraud detection) to be performed by a cosigning service.

The cosigning key can also be replaced or removed, allowing for full flexibility and fine grained control of permissions and authorization.

Multi-Signature Implementation

The wallet achieves multi-signature capabilities by way of the invoke() method and its variants. Performing all value transfers, administration of device keys and rotating the backup key and recovery transaction are required to be called through the invoke() method, thus allowing for a cosigning check on all aforementioned operations. The invoke() methods variants are capable of receiving up to two signatures, in addition to the "free" signature provided by msg.sender.

Recovery Operation

A RECOVERY operation is performed by submitting the recovery transaction to the blockchain network. The effects of this transaction are as follows:

  • Remove all existing device keys (scorched earth policy)
  • Add the backup key as the only device key

This operation is intended to be executed in the scenario where all the users device keys are LOST, STOLEN or COMPROMISED. The operation essentially “activates” the backup key, and as such the backup key is no longer considered a backup key but rather a full device key.

The user can then rotate the backup key and recovery transaction via their new device key.

For questions, inquiries or more please email support@meetdapper.com

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