December 2018
Intermediate to advanced
222 pages
6h 6m
English
Content preview from Blockchain Quick Start Guide
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Use the checks-effects-interactions pattern
Be very careful when interacting with other external contracts, it should be the last step in your function. It can introduce several unexpected risks or errors. External calls may execute malicious code. These kinds of calls should be considered as potential security risks and avoided if possible.
pragma solidity ^0.4.24;// THIS CONTRACT is INSECURE - DO NOT USEcontract Fund { mapping(address => uint) userBalances;function withdrawBalance() public { //external call if (msg.sender.call.value(userBalances[msg.sender])()) userBalances[msg.sender] = 0;}}contract Hacker { Fund f; uint public count; event LogWithdrawFallback(uint c, uint balance); function Attacker(address vulnerable) public { f = ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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