Explain Ethereum smart contract hacking like i am a five
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Ethereum allows for smart contracts which are programs stored on the blockchain that execute automatically based on predefined rules. Smart contracts are vulnerable to hacking through bugs and exploits like integer overflows. Major hacks have occurred on smart contracts, like The DAO hack which stole $50 million worth of ether. Writing secure smart contracts is challenging as seen through continued hacks, showing the technology is still immature.
![Since August 2018 the latest Metamask has been
showing the hex data to be sent
Kittie ID in hex
Identifier for the Bid function (MethodID) –
keccak256(“bid(uint256)”)[:4]
59 zeroes because the
world needs 2ˆ256 Kitties](https://image.slidesharecdn.com/hacktivity2018ethereumsmartcontracthackingexplainlikeiamafivecopy-copy-181015145457/85/Explain-Ethereum-smart-contract-hacking-like-i-am-a-five-21-320.jpg)
![The DAO hack …
// INSECURE --- this is not DAO code, but similar so it is easy to understand
function withdrawBalance() public { // 1st line
uint amountToWithdraw = userBalances[msg.sender]; // 2nd line
require(msg.sender.call.value(amountToWithdraw)()); // 3rd line. At this point, the caller's code is
executed, and can call withdrawBalance again
userBalances[msg.sender] = 0; // 4th line
}](https://image.slidesharecdn.com/hacktivity2018ethereumsmartcontracthackingexplainlikeiamafivecopy-copy-181015145457/85/Explain-Ethereum-smart-contract-hacking-like-i-am-a-five-28-320.jpg)
![Teh library codez
function initWallet(address[] _owners, uint _required, uint _daylimit) {
//the shared library has initWallet and it is public !
initDaylimit(_daylimit);
initMultiowned(_owners, _required);
}
initWallet is not in the non-library code, but is called in the shared library](https://image.slidesharecdn.com/hacktivity2018ethereumsmartcontracthackingexplainlikeiamafivecopy-copy-181015145457/85/Explain-Ethereum-smart-contract-hacking-like-i-am-a-five-35-320.jpg)
Explain Ethereum smart contract hacking like i am a five
- 1. EXPLAIN ETHEREUM SMART CONTRACT HACKING LIKE I AM FIVE Zoltan Balazs 2018 October
- 2. Whoami? Zombie Browser Toolkit https://github.com/Z6543/ZombieBrowserPack HWFW Bypass tool Similar stuff was used in PacketRedirect in Danderspritz FlewAvenue by EQGRP https://github.com/MRGEffitas/hwfwbypass Malware Analysis Sandbox Tester tool https://github.com/MRGEffitas/Sandbox_tester Played with crappy IoT devices – my RCE exploit code running on ~600 000 IP cameras via Persirai https://jumpespjump.blogspot.hu/2015/09/how-i-hacked-my-ip-camera-and-found.html https://jumpespjump.blogspot.hu/2015/08/how-to-secure-your-home-against.html Invented the idea of encrypted exploit delivery via Diffie-Hellman key exchange, to bypass exploit detection appliances Implemented by Angler and Nuclear exploit kit developers https://www.mrg-effitas.com/generic-bypass-of-next-gen-intrusion-threat-breach-detection-systems/ 2
- 3. Questions Hands up if you know something about blockchain Hands up if you have ever tried to explain Bitcoin to your parents/colleagues/kids Hands up if it ended: “it is complicated” Hands up if you have ever interacted with a Smart Contract
- 4. Why am I talking about this? ITSEC folks laugh about Blockchain a lot They believe it is not happening not important not working Bad news: it is happening! Trust me, this is an important topic I will calculate losses in Lamborghinis – 200K USD
- 5. So who am I to talk about this topic? I don’t give advice on investing/ selling/ HODLing cryptocurrencies
- 6. Main idea of cryptocurrencies Let’s go with metaphors on this topic Math is hard (at least for me it is true) Let’s form a group where we solve mathematical challenges MINING Everyone can easily check if someone solved the hard math challenge When someone solves a math challenge, they receive moneZ (my imaginary cryptocurrency)
- 7. Transactions If Bunny wants to send moneZ to Piggie, everyone will know and has to know about all details of the transaction In fact, everyone knows how much moneZ everyone has because it is public knowledge Sidenote: ETHEREUM different
- 8. Blockchain The last not yet processed moneZ are collected in a transaction together The bundle of transactions is included as additional parts to the math challenge to be solved blocks Including the transactions in the math challenges will cost moneZ for the initiator transaction fee A long paper trail is created where every blocks are recorded blockchain
- 9. How can newcomers get moneZ - Bitcoin, etc.? They can start to solve new math challenges Before that they should get a copy of the long paper trail - blockchain By solving math challenges and including the transactions, they get the transaction fee Or they can ask someone to send them moneZ In exchange they can give something - real money, Alpaca socks
- 10. What is a wallet The wallet holds all the moneZ you previously received Whenever you send moneZ from your wallet to someone else's wallet, you sign the transaction with your signature, which is impossible to counterfeit Transactions are irreversible and final* Everyone will know you transferred the money, you can’t draw back
- 11. Why is this interesting? You don’t have to be in the same room to do the math challenges You can do all the stuff through the Internet You don’t even have to know who the others are (pseudo-anonimity)
- 13. Smart Contracts Assume you have a basic understanding of cryptocurrencies in general Let’s take a deep dive into Smart Contracts Bitcoin is also capable of doing Smart Contracts Ethereum YAC (Yet Another Cryptocurrency) was designed for Smart Contracts
- 14. Smart Contracts You want to sign and get a countersign of the contract carve the contract into stone contracts carved into the stone cannot be modified In the smart contract world, the stone is the blockchain it is powered by the time and energy spent on solved math challenges Code is universal
- 15. What is gas? Smart contract is code which can be executed by anyone who solves the math challenges for moneZ - mines the cryptocurrencies Similarly to moneZ transaction fees, you have to pay moneZ to get the smart contract code executed by everyone The more complex the smart contract code is, the more moneZ you have to pay This is called gas in Ethereum
- 16. Are we there yet?
- 17. Ethereum Virtual Machine Bytecode: it is not a machine code, thus you need a VM to execute it Solidity: compile JavaScript-like code into EVM bytecode Source code can be published - creates trust Solidity source code compiles into the same bytecode (reproducible) At least with the same parameters and same compiler version
- 18. JavaScript developers today Solidity (smart contract language) looks similar to JavaScript You need web3.js based frontend - this is JS Many smart contract coders have JavaScript background JavaScript: You must move fast and break things With Ethereum Smart Contracts, this approach is not “profitable” … Solidity: Deploy once, be hacked anytime
- 21. Since August 2018 the latest Metamask has been showing the hex data to be sent Kittie ID in hex Identifier for the Bid function (MethodID) – keccak256(“bid(uint256)”)[:4] 59 zeroes because the world needs 2ˆ256 Kitties
- 22. Code can be hacked Smart contracts are code
- 26. The DAO: Recursive call + race condition June 18th, 2016 Attacker transfers Ether worth $250 million from DAO That is 1250 Lamborghinis Reentrancy at the splitDAO function
- 27. The DAO hack You can interrupt the bank teller while he is giving you money The bank teller only updates your balance at the end
- 28. The DAO hack … // INSECURE --- this is not DAO code, but similar so it is easy to understand function withdrawBalance() public { // 1st line uint amountToWithdraw = userBalances[msg.sender]; // 2nd line require(msg.sender.call.value(amountToWithdraw)()); // 3rd line. At this point, the caller's code is executed, and can call withdrawBalance again userBalances[msg.sender] = 0; // 4th line }
- 30. The solution? Rewrite the past and pretend it didn’t happen Attacker got away with his ETH Classic worth $67.4 million – 337 Lambos
- 32. Multi-signature wallets “Captain planet, the world’s first multi-factor authentication” © dnet
- 33. Shared vulnerable library + reinit - 2017 July 20 $31M stolen – 155 Lambos A lot more was in danger, but good guys were faster Lot of shared libraries exists in the blockchain Save gas Contracts now share the same vulnerabilities Parity multi-signature wallets
- 34. Teh code NON LIBRARY CODE function() payable { // someone called a function we don’t have? if (msg.value > 0) // some ether is sent ... else if (msg.data.length > 0) //ether is not sent, but some data is _walletLibrary.delegatecall(msg.data); //let’s check if we can execute this code via shared library } ● If the method name is not defined on this contract… ● And there’s no ether being sent in the transaction… ● And there is some data in the message payload… for whatever method that calls DELEGATECALL, it will call the same method on the contract you're delegating to, but using the context of the current contract
- 35. Teh library codez function initWallet(address[] _owners, uint _required, uint _daylimit) { //the shared library has initWallet and it is public ! initDaylimit(_daylimit); initMultiowned(_owners, _required); } initWallet is not in the non-library code, but is called in the shared library
- 36. So some random guys don’t know how to code Smart Contracts …
- 37. Fixing the Parity bug Parity fixed previous bug and introduced a new one Library contract was not initialized properly. That allowed anyone to turn the library contract into a multi-sig wallet
- 38. The next Parity hack November 2017 - $300M lost – 1500 Lambos @devops199 “accidentally” called initWallet() method to own the library @devops199 “accidentally” called kill() method to self-destruct it It was planned to be fixed – forking EIP-999. Community voted no
- 39. Intro to integer underflow Underflow If there are (unsigned integer 8) 3 people on the bus, and four of them took of the bus, how many people are still on the bus? 255
- 40. Intro to integer overflow Overflow If there are (unsigned integer 8) 255 people on the bus, and the bus is totally full, and one guy hops on the bus, how many people are on the bus?
- 41. Proof of Weak Hands https://medium.com/@optimumregret/the-surreal-madness- of-ethereums-pyramid-schemes-da705fe7d92e USD 2M lost unsigned integer underflow withdrawal Use Safemath! https://etherscan.io/tx/0x233107922bed72a4ea7c75a83ecf58dae4 b744384e2b3feacd28903a17b864e0
- 42. Conclusion Blockchain, Ethereum, Smart Contracts are here to hack Writing secure Smart Contracts is hard Ethereum is still in beta Hacking Smart Contracts is possible, fun, but probably illegal Hacking your own smart contract is probably not illegal Hacking in test blockchain is not illegal
- 43. Where to learn to code? cryptozombies.io
- 44. Where to learn to hack?
- 45. References Nick Szabo: The idea of smart contracts 1997 https://perma.cc/V6AZ-7V8W https://www.reddit.com/r/explainlikeimfive/comments/12knie/eli5_bitcoins/?st=IZW0ENOG&sh=d566a3ee https://medium.freecodecamp.org/smart-contracts-for-dummies-a1ba1e0b9575 https://www.reddit.com/r/explainlikeimfive/comments/4lz9t4/eli5_ethereum/ http://hackingdistributed.com/2016/06/18/analysis-of-the-dao-exploit/ https://github.com/b-mueller/smashing-smart-contracts/blob/master/smashing-smart-contracts-1of1.pdf https://medium.freecodecamp.org/a-hacker-stole-31m-of-ether-how-it-happened-and-what-it-means-for-ethereum- 9e5dc29e33ce https://www.stateofthedapps.com/ Cryptozombies.io - best tutorial Latest hype and scams: https://boards.4chan.org/biz/
- 46. 48 Hack the planet! [email protected] https://hu.linkedin.com/in/zbalazs Twitter – @zh4ck www.slideshare.net/bz98 HACKERSULI !!!1! Greetz to @VitalikButerin, Satoshi Nakamoto https://JumpESPJump.blogspot.com
Editor's Notes
- #2: TODO bevezeto
- #5: Who thinks Smart Contracts are the future?
- #9: We are going to … TODO nyelvtan
- #19: TODO image
- #22: Megvagni a videot
- #30: It’s like the bank teller won’t change your balance until he gives you all the money you have requested. “Can I withdraw $500? Wait, before that, can I withdraw $500?” The smart contract was designed only to check you have $500 at the beginning, once, and allow themselves to be interrupted.
- #35: 5 people would summon Captain Planet who would save the world