Blockchain Developer's Guide

Security considerations

It is important to understand smart contracts in the domain in which they live: decentralized, asynchronous networks. As a result of living in this ecosystem, there are security considerations that are not always obvious and can lead to issues. To illustrate, we are going to look into two related functions of the ERC20 standard: approve and transferFrom. Here is code for the approve function from OpenZeppelin:

function approve(address _spender, uint256 _value) public returns (bool) {   allowed[msg.sender][_spender] = _value;   emit Approval(msg.sender, _spender, _value);   return true; }

The approve function allows a token owner to say that they have approved a transfer of their token to another account. Then, in response ...