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Last active Jun 17, 2018
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Quick spike to demonstrate a generic account proxy pattern and a specific implementation for cold/hot wallets. Not reviewed, use it at your own risk.
contract AccountProxy {
event Fwded(address indexed to, uint256 value, bytes calldata, bool succeeded);
// must be implemented by super contract
function canFwd(address who, address to, uint256 value, bytes calldata) public view returns (bool);
function () payable {} // allow to deposit eth
function fwd(address to, uint256 value, bytes calldata) external {
require(canFwd(msg.sender, to, value, calldata));
bool succeeded =;
emit Fwded(to, value, calldata, succeeded);
contract HotColdProxy is AccountProxy {
address public hot;
address public cold;
mapping (bytes4 => bool) onlyColdFunctions;
mapping (address => bool) onlyColdAddresses;
constructor (address _cold, address _hot, bytes4[] _onlyColdFunctions, address[] _onlyColdAddresses) public {
cold = _cold;
hot = _hot;
for (uint i = 0; i < _onlyColdFunctions.length; i++) {
onlyColdFunctions[_onlyColdFunctions[i]] = true;
for (uint j = 0; j < _onlyColdAddresses.length; j++) {
onlyColdAddresses[_onlyColdAddresses[j]] = true;
onlyColdAddresses[this] = true;
function changeHot(address _hot) external {
require(msg.sender == address(this)); // proxy must call itself to allow flexibility
hot = _hot;
function changeCold(address _cold) external {
require(msg.sender == _cold); // could also require for proxy to call itself, but it is sensible to limit it to only cold
cold = _cold;
function canFwd(address who, address to, uint256 value, bytes calldata) public view returns (bool) {
if (who == hot) {
bool onlyCold = value > 0 || onlyColdAddresses[to] || onlyColdFunctions[sig(calldata)];
return !onlyCold;
return who == cold;
// TODO: Functions to change onlyCold addresses and functions
function sig(bytes calldata) internal pure returns (bytes4 sig) {
assembly { sig := mload(calldata) }
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