├── EthereumSmartContracts.md ├── LICENSE └── README.md /EthereumSmartContracts.md: -------------------------------------------------------------------------------- 1 | ## Ethereum smart contracts security recommendations and best practices: 2 | 1. In ERC20 approve first change to 0 and then to value 3 | 1. tokens should verify in approve that previously was 0 if changing not to 0 like in minime and also add increaseAllowance/decreaseAllowance preferring it over approve 4 | 2. https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/edit 5 | 3. https://github.com/ethereum/EIPs/issues/738 6 | 4. https://github.com/ethereum/EIPs/pull/610#issuecomment-304746812 was said to not be necessary: https://github.com/Giveth/minime/pull/18#issuecomment-337928059 7 | 5. minime solution is shortest and best and here is an explanation of why it is enough: https://github.com/ethereum/EIPs/issues/20#issuecomment-277542427 8 | 9 | 2. Using things like block.coinbase, block.difficulty, block.gaslimit, block.number, block.timestamp, tx.gasprice, or tx.origin in constant functions is not a good idea, because it is unspecified what EVM will return, and different implementations, or even different versions of the same implementation, may behave differently 10 | 1. https://github.com/ethereum/EIPs/pull/610#issuecomment-327514172 11 | 12 | 3. re-entrancy: transferring ether can trigger another contract which triggers back current contract causing money drain. this can be solved by Checks-Effects-Interactions pattern https://solidity.readthedocs.io/en/v0.5.8/security-considerations.html#re-entrancy 13 | 1. this caused the DAO hack https://ethereum.stackexchange.com/questions/6210/how-was-the-recursion-created-that-lead-to-thedao-hack 14 | 2. https://medium.com/spankchain/we-got-spanked-what-we-know-so-far-d5ed3a0f38fe 15 | 3. the smart contracts execution is single-threaded (but the order between transactions is unknown until they settle with enough confirmations) which makes it possible to use state variables as mutexes, however this adds gas cost so other solutions might be preferable 16 | 1. https://ethereum.stackexchange.com/questions/8261/how-to-solve-solidity-asynchronous-problem/8265#8265 17 | 2. https://github.com/sigp/solidity-security-blog#preventative-techniques 18 | 4. https://github.com/ethereum/wiki/wiki/Safety#pitfalls-in-race-condition-solutions 19 | 20 | 4. always first do checks and then state changes and only then external contracts calls or transfers https://solidity.readthedocs.io/en/v0.5.8/security-considerations.html#use-the-checks-effects-interactions-pattern 21 | 22 | 5. using "transfer" can cause problems and it is better to allow withdrawals instead. ALWAYS use ERC20 approve+transferFrom instead of transfer, which will help protect from transfers to bad address and other errors, see: https://solidity.readthedocs.io/en/v0.5.8/common-patterns.html#withdrawal-pattern 23 | 24 | 6. never trust transaction origin as identification (origin is always the EOA who made initial transaction while msg.sender can be a contract which made internal transaction as a result of the original transaction) https://solidity.readthedocs.io/en/v0.5.8/security-considerations.html#tx-origin 25 | 26 | 7. use openZepplin safemath to protect from math overflows and underflows for any mathematic operations https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-101 27 | 1. there is an EIP about evm opcodes protecting from overflows so use them when available https://eips.ethereum.org/EIPS/eip-1051 28 | 29 | 8. enable SMTChecker using appropriate pragma to allow formal verification https://solidity.readthedocs.io/en/v0.5.8/layout-of-source-files.html#smt-checker https://solidity.readthedocs.io/en/v0.5.8/security-considerations.html#formal-verification 30 | 31 | 9. dont add kill/self destruct or it can cause money loss: https://github.com/parity-contracts/0x863df6bfa4/pull/2 https://github.com/paritytech/parity-ethereum/issues/6995 32 | 33 | 10. https://medium.com/loom-network/how-to-secure-your-smart-contracts-6-solidity-vulnerabilities-and-how-to-avoid-them-part-2-730db0aa4834 34 | 1. point 4 in the link: calling selfdestruct with a contract address, sends ether to that address without calling the contract fallback function so never base decisions on the balance. 35 | 1. another way is using coinbase transaction of mining reward 36 | 2. another way is pre-fund an address before contract creation https://github.com/sigp/solidity-security-blog#pre-sent-ether 37 | 3. another way is if the constructor is payable then to transfer funds on contract creation 38 | 2. point 5 - always assume that transfers and external calls (of instance) can trigger revert 39 | 1. calling method from contract instance propogates errors and allows to get return value while calling using .call(..) does not require knowing the abi, on failure only returns false without reverting and does not allow getting the true return value https://ethereum.stackexchange.com/questions/30383/difference-between-call-on-external-contract-address-function-and-creating-contr 40 | 2. UPDATE: From solidity compiler version 0.5 the function .call DOES allow to get the return value, see: https://solidity.readthedocs.io/en/v0.5.8/050-breaking-changes.html#semantic-and-syntactic-changes 41 | 3. ALWAYS avoid the use of now and block.blockhash for your contract’s business logic as their results are predictable or can be manipulated by miners https://www.reddit.com/r/ethereum/comments/483rr1/do_not_use_block_hash_as_source_of_randomness/ 42 | 4. more things covered already in other bullets in the recommendations list here https://medium.com/loom-network/how-to-secure-your-smart-contracts-6-solidity-vulnerabilities-and-how-to-avoid-them-part-1-c33048d4d17d 43 | 44 | 11. .call() and .call().value() should be avoided (.value(..) adds ether to send and .gas(..) adds gas limit). they both dont limit gas (without calling .gas(..)) and return true/false instead of reverting on failure and they may cause re-entrance vulnerability https://ethereum.stackexchange.com/questions/43782/importance-of-call-value/43821#43821 45 | 46 | 12. use cases of using send,transfer,.call().value(..).gas(..)()(). basically most cases use transfer and if using call then always set .gas(..) or otherwise the other contract can do a DOS by doing assert which takes away all gas preventing code from continueing execution after the call https://ethereum.stackexchange.com/questions/19341/address-send-vs-address-transfer-best-practice-usage/38642#38642 https://github.com/ethereum/solidity/issues/610 47 | 48 | 13. always prefer to throw and revert than to return true/false (more safe against reentrance attacks) as from discussion here https://github.com/ethereum/solidity/issues/610 49 | 1. some good arguments about why better to return false instead of throw: https://github.com/ethereum/EIPs/pull/610#issuecomment-305770167 50 | 2. some good arguments about why better to throw than return false: https://github.com/ethereum/EIPs/issues/20#issuecomment-300500880 https://github.com/ethereum/EIPs/issues/20#issuecomment-300746940 51 | 52 | 14. in general it is safer to trigger exception than to return false because exception reverts any changes to the state while return false leaves the responsability for the caller to revert if needed https://ethereum.stackexchange.com/questions/15140/would-it-be-better-to-use-throw-instead-of-return-false/15147#15147 53 | 54 | 15. new solidity compiler versions removed throw keyword and it now has assert,require,revert 55 | 1. discussion on use cases of assert (in the end of 2018 open zepplelin changed safemath to use require instead of assert) https://github.com/OpenZeppelin/openzeppelin-solidity/issues/1120 56 | 2. require and revert return the rest of the gas to the user while assert uses all of the gas recevied 57 | 3. require is for input validations while assert is mainly for static code analysis to identify situations which should NEVER happen and create compile time warnings 58 | 1. https://ethereum.stackexchange.com/questions/27812/why-using-assert-since-it-would-consume-all-gas/27824#27824 59 | 2. https://ethereum.stackexchange.com/questions/15166/difference-between-require-and-assert-and-the-difference-between-revert-and-thro/50957#50957 60 | 4. require vs revert seems to be different syntax for the same thing: https://github.com/ethereum/solidity/issues/6689 61 | 62 | 16. if contract does not need to receive ether (erc20 token without buying period for example) then dont implement payable functions and dont implement fallback functions. dont create unnecessary attack interface. more code = more attack interface. transfer to the contract will revert automatically: https://ethereum.stackexchange.com/questions/34160/why-do-we-use-revert-in-payable-function/34164#34164 63 | 64 | 17. still need a way to get ether out even if fallback function is not implemented in case where ether will still be received using selfdestruct or transfered when calling some methods 65 | 66 | 18. should make error messages as short as possible while still being clear because error messages increase contract deployment gas (while not increasing executing gas) https://ethereum.stackexchange.com/questions/66879/does-a-string-message-increase-the-gas-usage-of-a-require-statement 67 | 68 | 19. on division make sure the number is even or otherwise it will get rounded DOWN 69 | 70 | 20. be careful of replay attacks and of different assumptions https://media.consensys.net/discovering-signature-verification-bugs-in-ethereum-smart-contracts-424a494c6585 71 | 1. for example previously a replay was possible between ethereum mainnet transaction and other chains, this was addressed in eip 155: https://eips.ethereum.org/EIPS/eip-155 72 | 73 | 21. Implement only the necessary functionality and try doing that in the shortest and most efficient way, to avoid creating unneccesary attack surface and room for bugs in the code 74 | 75 | 22. Use audited and tested code https://security.stackexchange.com/questions/18197/why-shouldnt-we-roll-our-own 76 | 77 | 23. Write as many unit tests as possible https://consensys.github.io/smart-contract-best-practices/software_engineering/#contract-rollout 78 | 79 | 24. perform security audits and implement security layers architecture to protect from the unknown https://dasp.co/#item-10 80 | 81 | 25. Inline assembly is a way to access the Ethereum Virtual Machine at a low level. This bypasses several important safety features and checks of Solidity. You should only use it for tasks that need it, and only if you are confident with using it https://solidity.readthedocs.io/en/v0.5.8/assembly.html#inline-assembly 82 | 83 | 26. even if selfdestruct is not implemented, it is still possible using delegatecall so libraries should never call delegatecall/callcode 84 | 85 | 27. careful with delegatecall because it preserves context and allows the called contract to modify state of original contract. so the caller is at the merci of the called contract https://ethereum.stackexchange.com/questions/11578/how-to-protect-against-delegatecall-in-a-hub-spoke-contract-model/11598#11598 86 | 87 | 28. callcode also allows called contract to modify original contract storage just like delegatecall 88 | 1. https://ethereum.stackexchange.com/questions/3667/difference-between-call-callcode-and-delegatecall 89 | 2. to detect if your smart contract is called by callcode/delegatecall: https://ethereum.stackexchange.com/questions/69551/how-to-prevent-the-code-of-my-contract-being-used-in-a-callcode/69552 90 | 91 | 29. libraries called with delegatecall to modify original contract state, SHOULD NOT STORE STATE of themselves. because their state is actually pointing to storage slots of the caller contract which used delegatecall. use "library" keyword instead of "contract" keyword for libraries to detect problems at compile time (ensures the library contract is stateless and non-self-destructable) https://github.com/sigp/solidity-security-blog/blob/master/README.md#preventative-techniques-3 92 | 93 | 30. order of state variables matters! sort them from smallest to biggest type so that the storage allocated will be minimal which will require less gas to deploy 94 | 1. mappings and dynamically-sized arrays don't follow normal storage rules 95 | 2. when byte32 is converted to byte16 its taken from the left (0x922aba368bee9844aefc4b47b1d58d2857781b382dc1ad896d512e19131d108f -> 0x922aba368bee9844aefc4b47b1d58d28) https://gist.github.com/kenjirai/d1b9c135117eb39d7891d658cbd6154c 96 | 3. when uint32 is converted to uint16 then the smallest bytes are taken 0x12345678 -> 0x5678 97 | 98 | 31. private members of contract are accessible (for example using web3.eth.getStorageAt) so don't store any private information in the contract. zksnarks and zero knowledge proofs and private key signature can allow proof of secret without revealing the secret 99 | 1. getStorageAt returns 32 bytes content of desired storage slot which is a 32 bytes storage unit 100 | 101 | 32. constant variables of contract are not stored in storage 102 | 103 | 33. even if interface states that function is view/pure, the function implementation contract can define the function without view/pure and modify state. so can't assume state is not modified by interface declaration alone 104 | 105 | 34. when relevant to call something without letting it change state: STATICCALL opcode makes sure the called function does not modify state which new solidity compilers use for view/pure functions https://eips.ethereum.org/EIPS/eip-214 106 | 107 | 35. careful with EXTCODESIZE and CODESIZE because they behave differently during contract initialization: contract address is calculated from contract creation info and code initialization code is executed BEFORE the code is associated to the contract address so "During initialization code execution, EXTCODESIZE on the address should return zero, which is the length of the code of the account while CODESIZE should return the length of the initialization code" https://medium.com/coinmonks/ethernaut-lvl-14-gatekeeper-2-walkthrough-how-contracts-initialize-and-how-to-do-bitwise-ddac8ad4f0fd 108 | 1. "Put simply, if you try to check for a smart contract’s code size before or during contract construction, you will get an empty value. This is because the smart contract hasn’t been made yet, and thus cannot be self cognizant of its own code size" 109 | 110 | 36. contract which has problems at initialization will have an address but have no code 111 | 112 | 37. structs 113 | 1. struct declarations default to storage so ALWAYS use "memory" keyword in initialization of temporary struct inside function to prevent it being saved to storage. also because of this better to avoid structs for temporary calculations 114 | 2. if you declare a new storage struct in your function, it will overwrite other globally stored variables (starting from the first slot) 115 | 3. when you directly save a memory struct into a state variable, the memory struct is automatically forced into storage 116 | 4. function inputs are memory and not storage backed 117 | 5. you cannot implicitly convert memory into storage in assignment of function input struct to storage variable struct 118 | 6. although you cant return structs from functions, you can create mapping state variables with struct values and a default getter will be created for it which returns struct 119 | 120 | 38.when calling contract from remix better to always wrap big numbers with quotes to avoid problems and truncating 121 | 122 | 39. contract address is deterministically calculated from transaction so it is possible to recover lost funds if can send transaction of contract creation which creates address where funds are at (or to prefund a contract this way before its creation) 123 | 1. https://github.com/sigp/solidity-security-blog#keyless-ether 124 | 2. address is calculated from sender address and nonce. for contract the nonce starts from 1 (0 used for contract self creation): address(keccak256(0xd6, 0x94, YOUR_ADDR, 0x01)). next contracts address can be calculated by incrementing nonce in the formula 125 | 3. https://medium.com/coinmonks/ethernaut-lvl-18-recovery-walkthrough-how-to-retrieve-lost-contract-addresses-in-2-ways-aba54ab167d3 126 | 127 | 40. if many contracts are deployed and want to optimize deployment gas by making contracts smaller then can deploy contract bytecode directly which can make contract opcode as small as for example 12 opcodes for initialization and 10 opcodes for runtime, see: https://medium.com/coinmonks/ethernaut-lvl-19-magicnumber-walkthrough-how-to-deploy-contracts-using-raw-assembly-opcodes-c50edb0f71a2 128 | 129 | 41. arrays 130 | 1. arrays declarations default to storage so ALWAYS use "memory" keyword in initialization of temporary arrays inside function to prevent it being saved to storage 131 | 2. dynamic arrays are ones defined with empty [] 132 | 3. Dynamic arrays must be initialized as "storage" variables 133 | 4. You can resize dynamic storage arrays but You cannot resize memory arrays, nor fixed size arrays 134 | 5. when you call solidity method you pass array size and it is not checked against actual payload. this allows to pass arrays of size bigger than possible to actually be generated and might allow other exploits so it needs to be taken into account when developing contracts (that array length is not bound by solidity) 135 | 6. arbitrary array length change and index access in array should not be allowed because it can possibly allow to access any contract storage using the array indexer 136 | 7. changing array length can be done by changing the array length property. need to be careful of underflows 137 | 8. https://ylv.io/ethernaut-alien-codex-solution/ 138 | 9. https://f3real.github.io/Ethernaut_wargame2022.html 139 | 140 | 42. be aware that maps and arrays and any other variables, are not really allocated in an independent location, they are all together in the storage slots of the contract and are references to some positions in that storage (array and maps positions in the storage are calculated using a special formula), thus for example it is possible to access the same storage using a map and an array if the array is big enough 141 | 142 | 43. be aware that revert reverts everything including events except gas spent https://ethereum.stackexchange.com/questions/4085/is-it-a-good-practice-to-log-an-event-every-time-i-throw-in-solidity 143 | 144 | 44. https://blog.zeppelin.solutions/onward-with-ethereum-smart-contract-security-97a827e47702 145 | 1. Avoid declaring variables using var if possible, otherwise the type will be the smallest possible (for i=1 the type will be uint8 maxing at 255) 146 | 1. UPDATE: from solidity compiler version 0.5 using var is disallowed https://solidity.readthedocs.io/en/v0.5.8/050-breaking-changes.html#variables 147 | 2. the recommended naming for custom events is that they should start with "Log" to make them easily identified 148 | 149 | 45. add fail strings to require and revert commands for easier error finding and bugs detection 150 | 151 | 46. short address attack: if user address ends with one or more zeroes then by ommiting the zeroes if the sending system does not check the address length and create a transaction then the zero will be padded and will cause the transaction value to be added a zero causing undesired amount transfer 152 | 1. https://dasp.co/#item-9 153 | 2. mitigation using assert(msg.data.length == numOfParams * 32 + 4) creates bugs for multisig wallets working with the token 154 | 1. https://github.com/Giveth/minime/issues/8#issuecomment-348762658 155 | 2. https://vessenes.com/notice-about-fun-token-support-for-multisignature-wallets-2/ 156 | 3. funfair token paid for gas of transition to new contract https://funfair.io/new-fun-token-contract/ 157 | 3. mitigating by >= instead of == is also problematic https://blog.coinfabrik.com/smart-contract-short-address-attack-mitigation-failure/ 158 | 4. OpenZeppelin removed the short address attack validations from smart contracts because of the bugs they caused https://github.com/OpenZeppelin/openzeppelin-solidity/issues/261 159 | 5. was fixed in solidity 0.5.0 so no need to perform anything in the smart contract however SHOULD perform address validations in the deposit/withdrawal interfaces in our system https://github.com/ethereum/solidity/pull/4224 160 | 161 | 47. must compile with latest solidity versions to get latest security fixes, for example the short address attack fix in solidity 0.5.0 https://github.com/ethereum/solidity/pull/4224 162 | 1. https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-102 163 | 164 | 48. can't just do the hard work and security during contract development and then relax after deployment since solidity and evm upgrades many times enter new vulnerabilities to previously safe code, so need to always be up to date and ready to respond and to plan risk management for such cases. Example: https://medium.com/chainsecurity/constantinople-enables-new-reentrancy-attack-ace4088297d9 165 | 1. another example where geth protocol change caused a bug and loss of funds https://steemit.com/cryptocurrency/@barrydutton/breaking-the-biggest-canadian-coin-exchange-quadrigacx-loses-67-000-usdeth-due-to-coding-error-funds-locked-in-an-executable 166 | 2. example of place to periodically read is the solidity release notes to see bug fixes and behavior changes: https://github.com/ethereum/solidity/releases 167 | 168 | 49. don't base the smart contract code (passing .gas(2301) for example) on operations taking specific amount of gas such as transfer taking 2300 gas because those may change at any moment as discussed here: https://ethereum-magicians.org/t/remediations-for-eip-1283-reentrancy-bug/2434 169 | 170 | 50. CREATE2 opcode allows modifying contract code without modifying the address (redeploying to same address) which might be useful for some things but is considered a hack so the ability might be removed in future ethereum upgrades and can be used for attacks by redeploying malicious code in place of valid code 171 | 1. resources 172 | 1. https://medium.com/@jason.carver/defend-against-wild-magic-in-the-next-ethereum-upgrade-b008247839d2 173 | 2. https://ethereum-magicians.org/t/potential-security-implications-of-create2-eip-1014/2614 174 | 3. openzepplin zos is considering using it https://github.com/zeppelinos/zos/issues/152 175 | 4. code creating redeployable metamorphic contracts using CREATE2: https://github.com/0age/metamorphic 176 | 5. https://blog.ricmoo.com/wisps-the-magical-world-of-create2-5c2177027604 177 | 6. https://github.com/ricmoo/will-o-the-wisp 178 | 7. https://github.com/Zoltu/deterministic-deployment-proxy 179 | 2. ways to protect a smart contract from redeployable smart contracts (CREATE2) 180 | 1. dont interact with destructible contracts and libraries which use selfdestruct or CALLCODE or DELEGATECALL 181 | 2. validate that contract was created by EOA or by CREATE and the parent contract all the way up was created by EOA or by CREATE and not by CREATE2 182 | 183 | 51. SWC (Smart Contract Weakness Classification) collects known smart contracts weaknesses 184 | 1. resources 185 | 1. https://ethereum-magicians.org/t/eip-1470-smart-contract-weakness-classification-swc/1532 186 | 2. https://github.com/SmartContractSecurity/SWC-registry 187 | 3. https://github.com/ethereum/EIPs/issues/1469 188 | 4. https://smartcontractsecurity.github.io/SWC-registry/ 189 | 2. several weaknesses which do not appear previously in this list 190 | 1. functions and variables visibility should always be set appropriately to prevent unauthorized access https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-100 191 | 1. All function names are in lower camelCase (eg. sendCoin) and all event names are in upper CamelCase (eg. CoinTransfer). Input variables are in underscore-prefixed lower camelCase (eg. _offerId), and output variables are _r for pure getter (ie. constant) functions, _success (always boolean) when denoting success or failure, and other values (eg. _maxValue) for methods that perform an action but need to return a value as an identifier. Addresses are referred to using _address when generic, and otherwise if a more specific description exists (eg. _from, _to) https://github.com/ethereum/wiki/wiki/Standardized_Contract_APIs 192 | 2. UPDATE: From solidity compiler version 0.5 the compiler enforces explicit functions visibility declarations https://solidity.readthedocs.io/en/v0.5.8/050-breaking-changes.html#explicitness-requirements 193 | 2. in non-library contracts, the solidity compiler pragma in the contract should be locked to a specific version in which the contract was tested to avoid vulnerabilities being introduced by compilation in a different compiler version (supporting multiple compiler versions is more appropriate for libraries used by other contracts) https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-103 194 | 1. https://github.com/0xjac/ERC777/issues/61#issuecomment-479983564 195 | 3. always validate .call return value https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-104 https://github.com/sigp/solidity-security-blog#9-unchecked-call-return-values-1 196 | 4. never use assert unless asserting a bug which should NEVER happen. don't use it for logic reverts or for validations since it consumes all the gas that was sent to the transaction https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-110 197 | 5. fix all warnings which can be fixed and don't use deprecated functions https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-111 198 | 6. avoid race conditions and don't trust the miner https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-114 https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-116 199 | 1. https://dasp.co/#item-7 200 | 2. https://dasp.co/#item-8 201 | 3. https://github.com/sigp/solidity-security-blog#10-race-conditions--front-running-1 202 | 4. https://github.com/sigp/solidity-security-blog#12-block-timestamp-manipulation-1 203 | 7. don't assume that signatures are unique and don't hash the signatures https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-117 204 | 8. avoid shadowing variables https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-119 205 | 1. All function names are in lower camelCase (eg. sendCoin) and all event names are in upper CamelCase (eg. CoinTransfer). Input variables are in underscore-prefixed lower camelCase (eg. _offerId), and output variables are _r for pure getter (ie. constant) functions, _success (always boolean) when denoting success or failure, and other values (eg. _maxValue) for methods that perform an action but need to return a value as an identifier. Addresses are referred to using _address when generic, and otherwise if a more specific description exists (eg. _from, _to) https://github.com/ethereum/wiki/wiki/Standardized_Contract_APIs 206 | 9. don't trust blockchain randomness without oracles https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-1204 207 | 1. https://dasp.co/#item-6 208 | 2. https://www.reddit.com/r/ethereum/comments/74d3dc/smartbillions_lottery_contract_just_got_hacked/ 209 | 10. when dealing with signatures make sure to protect from replay attacks https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-121 210 | 11. do not "bring your own crypto" https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-122 https://security.stackexchange.com/questions/18197/why-shouldnt-we-roll-our-own 211 | 12. in multiple inheritance inherit from the more general to the more specific (the compiler will linearize the inheritance from right to left) https://consensys.github.io/smart-contract-best-practices/recommendations/#multiple-inheritance-caution https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-125 212 | 13. be careful or even avoid using function pointers or letting user input set their value https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-127 213 | 14. avoid dynamic length loops or actions because if they increase with time then the contract can become unusable gas-wise https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-128 https://github.com/sigp/solidity-security-blog#the-vulnerability-10 214 | 1. dynamic length loop vulnerability and proposed solution in the following audit https://mainframe.com/Mainframe_Secondary_Audit.pdf 215 | 15. check unicode characters of contract code to make sure they are all ascii before trusting what you see because right-to-left-override and similar unicode characters can mass up the code (can't trust etherscan verified code for example without this check) https://smartcontractsecurity.github.io/SWC-registry/docs/SWC-130 216 | 16. Use interface type instead of the address for type safety (note that this will still not protect from malicious external implementation so never trust external calls and use validation-effects-calls pattern) https://consensys.github.io/smart-contract-best-practices/recommendations/#use-interface-type-instead-of-the-address-for-type-safety 217 | 218 | 52. when testing contract using metamask DONT FORGET to change metamask to test network or use metamask without real ether or otherwise can mistakenly use real ether and lose it 219 | 220 | 53. be aware that state variables are mutatable under enough confirmations (12+) happen for the modification transaction block https://ethereum.stackexchange.com/questions/8261/how-to-solve-solidity-asynchronous-problem/8265#8265 221 | 1. so to make sure a previous function call was confirmed, need to save block height at previous call and compare it with block height at current call 222 | 2. when transactions settle the uncle blocks do not modify state even though they give mining rewards to miners https://ethereum.stackexchange.com/questions/57727/are-uncle-blocks-unnecessary-overhead-on-blockchain 223 | 224 | 54. consider making tokens pausable to have mitigations in case of a hack such as happened for BEC token where the pause ability saved a lot of money: https://medium.com/secbit-media/a-disastrous-vulnerability-found-in-smart-contracts-of-beautychain-bec-dbf24ddbc30e https://nvd.nist.gov/vuln/detail/CVE-2018-10299 225 | 1. MFT is another contract with vulnerability found which was saved by being pausable: https://blog.mainframe.com/important-mft-contract-redeployed-4f0b0bd8dc3b 226 | 2. EOS, Tron, Icon, OmiseGo, Augur, Status, Aelf, Qash, and Maker tokens are pausable https://blog.cryptofin.io/what-we-learned-from-auditing-the-top-20-erc20-token-contracts-7526ef3b6fb1 227 | 3. although discussing security tokens, the arguments in the following link about why to make the token pausable are partially valid for utility tokens too: https://github.com/ethereum/EIPs/issues/1400#issuecomment-420490082 228 | 4. allows tokens to be freezed in order to move them in the future to a different blockchain if wanted/necessary which is an important ability 229 | 5. considered an "emergency stop mechanism" https://github.com/OpenZeppelin/openzeppelin-solidity/issues/401#issuecomment-325387093 230 | 6. regarding trust, one can say that users should NOT trust tokens which are NOT pausable because they can lose their money with such tokens more easily where pausable tokens can pause in emergency and the users balances are publicly known and it would be a criminal act for the token issuer to just "walk away" with the money for no reason after pausing the token 231 | 7. the following reddit thread was opened at the time of the infamous DAO hack WHILE IT WAS HAPPENING and you can read the comments to see how the DAO users helplessly watched their money drained without any way to stop it. they would surely prefer a pause ability https://www.reddit.com/r/ethereum/comments/4oi2ta/i_think_thedao_is_getting_drained_right_now/ 232 | 8. unlike redeployable tokens which break the trust more than pausable token (because pausable tokens are part of something the user agreed to while redeployable tokens can introduce a whole new undesired contract code. and also pausable tokens dont modify balances while upgradable tokens can cause modifications), the pausing ability is even more important than upgrading ability for security reasons. that is because the pause serves as a response to attack while the upgrade can be looked at as a second step of restoration and it can also be done manually by deploying a fixed contract and updating the balances in it. 233 | 9. it is written here to pause the contract in "prepare for failure": https://github.com/ethereum/wiki/wiki/Safety#general-philosophy 234 | 235 | 55. make sure that smart contracts you interact with don't use dynamic address for contracts they call because then those innocent contracts could be malicious https://github.com/sigp/solidity-security-blog#preventative-techniques-6 236 | 1. honeypot used it: 237 | 1. https://www.reddit.com/r/ethdev/comments/7x5rwr/tricked_by_a_honeypot_contract_or_beaten_by/ 238 | 2. https://www.reddit.com/r/ethdev/comments/7xu4vr/oh_dear_somebody_just_got_tricked_on_the_same/dubakau/ 239 | 240 | 56. when testing a contract it is better to test it using a forked mainnet than testnet just in case of small critical differences. testing by forking mainnet can be done using genache: https://www.reddit.com/r/ethdev/comments/7x5rwr/tricked_by_a_honeypot_contract_or_beaten_by/du7i96z/ 241 | 242 | 57. be careful of divisions and losing precision https://github.com/sigp/solidity-security-blog#15-floating-points-and-precision 243 | 244 | 58. if someone withdraws money from an EOA address it does not mean he has the private keys for that address (done by taking a random signature and calculating the address from it and using the signature to withdraw from that address) 245 | 1. https://github.com/sigp/solidity-security-blog#one-time-addresses 246 | 2. https://medium.com/@weka/how-to-send-ether-to-11-440-people-187e332566b7 247 | 248 | 59. total amount of ether is not an invariant depending on mining if selfdestruct is called with its own address to send ether to (this was possibly fixed by now). same if after suicide the contract kills another contract which sends fund to the original suicided contract https://swende.se/blog/Ethereum_quirks_and_vulns.html quick#2 249 | 250 | 60. checking if address is a contract by checking extcodesize doesn't work in execution of contract constructor. note that checking if original sender is a contract can be done by "msg.sender != tx.origin", see quirk4 here: https://swende.se/blog/Ethereum_quirks_and_vulns.html 251 | 252 | 61. make sure to use wrapper around ERC20 interface when interacting with ERC20 tokens from new solidity compiler to be able to interact with many tokens (including BNB and OMG) which implemented ERC20 without return value. can use SafeERC20 library of open zeppelin for this purpose 253 | 1. https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca 254 | 2. https://docs.openzeppelin.org/docs/token_erc20_safeerc20 255 | 3. some exchanges use other wrappers: https://github.com/ethereum/solidity/issues/4116#issuecomment-439824542 256 | 257 | 62. "running a sale that accepts multiple currencies at a fixed exchange rate is dangerous and bad" https://vitalik.ca/general/2017/06/09/sales.html 258 | 259 | 63. be careful about assumptions of user being in control of his account/keys because many accounts are in control of exchanges and not users https://github.com/ConsenSys/singulardtv-contracts/issues/59 260 | 261 | 64. should use checkInvariants modifier like here: https://github.com/ethereum/wiki/wiki/Safety#assert-guards 262 | 263 | 65. when deploying use solidity optimizations to lower gas 264 | 265 | 66. must not add a check in erc20 approve of amount being not bigger than user balance because that prevents infinite approval and approval in advance 266 | 1. https://github.com/sec-bit/awesome-buggy-erc20-tokens/blob/master/ERC20_token_issue_list.md#a19-approve-with-balance-verify 267 | 268 | 67. when interacting with the contract sometimes it can be good to first do a call and only if success then to send transaction https://gist.github.com/ethers/2d8dfaaf7f7a2a9e4eaa 269 | 270 | 68. consider adding validation that transfer does not transfer to contract address, see validDestination modifier implementation here (or if not adding it then add a way for owner to withdraw contract tokens balance): https://consensys.github.io/smart-contract-best-practices/tokens/ 271 | 272 | 69. consider adding a comment in code published to etherscan with information of who to contact for issues found in the contract https://consensys.github.io/smart-contract-best-practices/documentation_procedures/ 273 | 274 | 70. Beware of negation of the most negative signed integer (Probably the solution should be to check for some invariant in the end of the calculation and not just -1) https://consensys.github.io/smart-contract-best-practices/recommendations/#beware-of-negation-of-the-most-negative-signed-integer 275 | 276 | 71. make sure that there are no shadows built ins https://consensys.github.io/smart-contract-best-practices/recommendations/#be-aware-that-built-ins-can-be-shadowed 277 | 278 | 72. pay attention that safemath only works with uint256, so be careful when working with other types without safemath 279 | 280 | 73. add speed bumps delays for sensitive actions which are rare enough or/and can be delayed (also make sure to add a way to pause/cancel in case of problem unlike DAO unstoppable speed bump which was useless), this will allow time to verify/detect/respond to attacks https://consensys.github.io/smart-contract-best-practices/software_engineering/#speed-bumps-delay-contract-actions 281 | 282 | 74. consider adding rate limiting where possible from business perspective https://consensys.github.io/smart-contract-best-practices/software_engineering/#rate-limiting 283 | 284 | 75. prefer more granural roles than just "owner". open zeppelin is doing it now: 285 | 1. https://github.com/OpenZeppelin/openzeppelin-solidity/issues/1146 286 | 2. https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1274 287 | 288 | 76. make sure gas is limited in external calls to prevent attacks such as GasToken minting https://cryptopotato.com/ethereums-malicious-gastoken-minting-could-result-in-a-disaster-for-crypto-exchanges/ 289 | 290 | 77. it is recommended to disable a contract instead of using self destruct if that contract is sent ether by users https://solidity.readthedocs.io/en/v0.5.8/introduction-to-smart-contracts.html#deactivate-and-self-destruct 291 | 292 | 78. to securely sign data offchain and pass it to a contract use eip 712 (by using web3.eth.personal.sign) and dont forget to add anti-replay nonce to the data signed and dont forget to add contract address to signature in case contract is redeployed to prevent replay to redeployed contract (cross contract replay attack) 293 | 1. https://github.com/ethereum/EIPs/pull/712 294 | 2. https://solidity.readthedocs.io/en/v0.5.8/solidity-by-example.html#what-to-sign 295 | 296 | 79. to make the contract clearer to users and avoid some misunderstandings, it is recommended to use natspec for any public/external functions/variables in the code and tools can use that to display it to end users 297 | 1. https://solidity.readthedocs.io/en/v0.5.8/style-guide.html#natspec 298 | 2. it needs to be published to swarm after compilation (otherwise one whitespace change can make the hash different) 299 | 3. the hash of the json metadata is embedded inside the contract bytecode suffix https://solidity.readthedocs.io/en/v0.5.8/metadata.html#encoding-of-the-metadata-hash-in-the-bytecode 300 | 4. https://solidity.readthedocs.io/en/v0.5.8/natspec-format.html 301 | 5. truffle does not support natspec yet: https://github.com/trufflesuite/truffle/issues/1118 302 | 6. metamask does not support natspec yet: https://github.com/MetaMask/metamask-extension/issues/2501 303 | 7. radspec is an implementation of natspec referenced by solidity documentation https://github.com/aragon/radspec#aside-why-is-natspec-unsafe 304 | 8. here it says it is hard to find the swarm where the json was deployed: https://blog.zeppelin.solutions/deconstructing-a-solidity-contract-part-vi-the-swarm-hash-70f069e22aef 305 | 9. Supporting natspec for state variables is stale for 1.5 years: https://github.com/ethereum/solidity/issues/3418 306 | 10. Here it says that radspec and natspec are not compatible: https://github.com/aragon/radspec/issues/67 307 | 11. seems natspec is not well supported right now but may be better supported in the future 308 | 309 | 80. dont trust hash of msg.data because some unused bits can be used to change the hash of msg.data https://solidity.readthedocs.io/en/v0.5.8/security-considerations.html#minor-details 310 | 311 | 81. enable SMTChecker when it will go to production https://solidity.readthedocs.io/en/v0.5.8/layout-of-source-files.html#smt-checker 312 | 313 | 82. Take care if you perform calendar calculations using these units, because not every year equals 365 days and not even every day has 24 hours because of leap seconds. Due to the fact that leap seconds cannot be predicted, an exact calendar library has to be updated by an external oracle https://en.wikipedia.org/wiki/Leap_second 314 | 315 | 83. careful when using blockhash. The block hashes are not available for all blocks for scalability reasons. You can only access the hashes of the most recent 256 blocks, all other values will be zero 316 | 317 | 84. be aware that packed abi encoding can be ambigious and hash collisions are possible for it https://solidity.readthedocs.io/en/v0.5.8/units-and-global-variables.html#abi-encoding-and-decoding-functions 318 | 319 | 85. If you use ecrecover, be aware that a valid signature can be turned into a different valid signature without requiring knowledge of the corresponding private key https://solidity.readthedocs.io/en/v0.5.8/units-and-global-variables.html#mathematical-and-cryptographic-functions 320 | 321 | 86. ethereum blockchain implements some functions (sha256, ripemd160 or ecrecover) as "precompiled" contracts which are deployed after their first use and thus first usage takes more gas and might run out of gas. relevant only for private blockchains https://solidity.readthedocs.io/en/v0.5.8/units-and-global-variables.html#mathematical-and-cryptographic-functions 322 | 323 | 87. note that if C is a contract then type(C).creationCode and type(C).runtimeCode have a lot of gotchas so be careful using them https://solidity.readthedocs.io/en/v0.5.8/units-and-global-variables.html#type-information 324 | 325 | 88. You should avoid excessive recursion, as every function call uses up at least one stack slot and there are at most 1024 slots available. for external calls (external calls generate message call while internal non prefixed calls are translated into jump opcodes) only 63/64th of the gas can be forwarded in a message call, which causes a depth limit of a little less than 1000 in practice 326 | 327 | 89. The low-level functions call, delegatecall and staticcall return true as their first return value if the called account is non-existent, as part of the design of EVM. Existence must be checked prior to calling if desired https://solidity.readthedocs.io/en/v0.5.8/control-structures.html#error-handling-assert-require-revert-and-exceptions 328 | 329 | 90. When dealing with function arguments or memory values, there is no inherent benefit to use types less than 256 bits because the compiler does not pack these values https://solidity.readthedocs.io/en/v0.5.8/miscellaneous.html#layout-of-state-variables-in-storage 330 | 331 | 91. use "indexed" keyword for events parameters which you wish to be indexed as topics. up to 4 indexed parameters are allowed per event. to have both the values and fast search, can add same value both as indexed parameter and as a not indexed parameter https://solidity.readthedocs.io/en/v0.5.8/abi-spec.html#events 332 | 333 | 92. It is highly suspicious if a contract was compiled with a compiler that contains a known bug and the contract was created at a time where a newer compiler version containing a fix was already released (note that most bugs are not critical but should periodically check the bugs list anyway, especially for new versions in the bottom here https://github.com/ethereum/solidity/blob/develop/docs/bugs_by_version.json) https://solidity.readthedocs.io/en/v0.5.8/bugs.html 334 | 335 | 93. The operators || and && apply the common short-circuiting rules. This means that in the expression f(x) || g(y), if f(x) evaluates to true, g(y) will not be evaluated even if it may have side-effects 336 | 337 | 94. The type byte[] is an array of bytes, but due to padding rules, it wastes 31 bytes of space for each element (except in storage). It is better to use the bytes type instead. As a general rule, use bytes for arbitrary-length raw byte data and string for arbitrary-length string (UTF-8) data. If you can limit the length to a certain number of bytes, always use one of the value types bytes1 to bytes32 because they are much cheaper https://solidity.readthedocs.io/en/v0.5.8/types.html#fixed-size-byte-arrays https://solidity.readthedocs.io/en/v0.5.8/types.html#bytes-and-strings-as-arrays 338 | 339 | 95. make sure that hardcoded literal addresses pass the checksum test or otherwise they are treated as regular rational numbers https://solidity.readthedocs.io/en/v0.5.8/types.html#address-literals 340 | 341 | 96. Underscores should be used to separate the digits of a numeric literal to aid readability and prevent mistakes, they do not influence the number https://solidity.readthedocs.io/en/v0.5.8/types.html#rational-and-integer-literals 342 | 343 | 97. pay attention that "string" type is UTF8 encoded so by "bytes(s)[7] = 'x';" Keep in mind that you are accessing the low-level bytes of the UTF-8 representation, and not the individual characters https://solidity.readthedocs.io/en/v0.5.8/types.html#bytes-and-strings-as-arrays 344 | 345 | 98. note that delete has no effect on mappings https://solidity.readthedocs.io/en/v0.5.8/types.html#delete 346 | 347 | 99. explicit overflowing conversions of negative integers is possible so be careful https://solidity.readthedocs.io/en/v0.5.8/types.html#explicit-conversions 348 | 349 | 100. always re-check the event data and do not rely on the search result based on the indexed parameters alone because the encoding of a struct is ambiguous if it contains more than one dynamically-sized array https://solidity.readthedocs.io/en/v0.5.8/abi-spec.html#encoding-of-indexed-event-parameters 350 | 351 | 101. readable and consistent code will lead to easier bug detection during development and eventually lead to a more secure code so follow the conventions here: https://solidity.readthedocs.io/en/v0.5.8/style-guide.html 352 | 353 | 102. library view functions do not have run-time checks that prevent state modifications https://solidity.readthedocs.io/en/v0.5.8/contracts.html#view-functions 354 | 355 | 103. Pure state reading are not enforced by evm https://solidity.readthedocs.io/en/v0.5.8/contracts.html#pure-functions 356 | 357 | 104. anonymous keyword for events makes the event name not be stored which makes the contract gas cheaper to deploy and call the event cheaper too. should be used when contract has only one event where the event name is not enforced by some standard because then all logs are known to be from this event and no need to store the event name https://github.com/ethereum/solidity/pull/6791#issuecomment-493989944 358 | 359 | 105. for tokens contract (and some other sensitive contracts too), in addition to being pausable, there should be an upgrading/migration strategy as described here: https://github.com/ethereum/EIPs/issues/644#issuecomment-494106553 360 | 1. See SafeUpgradeableTokenERC20 contract implementation here: https://github.com/guylando/EthereumSmartContracts 361 | 362 | 106. add events where possible/useful to make auditing and debugging and findings misbehaviors easier for deployed contracts 363 | 364 | 107. in tokens transfer functions prevent mistaken transfers to the token address by adding something like require( _to != address(this) ), see section 3.1 here: https://github.com/EthereumCommonwealth/Auditing/issues/236 365 | 366 | 108. in tokens decreaseAllowance function set to zero if bigger than balance instead of reverting so that for example when someone wants to remove allowance from the attacker quickly using decreaseAllowance then to stop revert from happening which would give more time to the attacker to use his allowance, see section 3.2 here: https://github.com/EthereumCommonwealth/Auditing/issues/236 367 | 368 | 109. to get familiar with possible vulnerabilities and get ideas, Go over previous reports in https://github.com/EthereumCommonwealth/Auditing/issues?q=is%3Aissue+is%3Aclosed and when done developing the contract consider submitting it for auditing to https://github.com/EthereumCommonwealth/Auditing 369 | 370 | 110. be careful when using SafeERC20 with non compliant token which has a non-reverting fallback function because SafeERC20 functions such as safeTransferFrom will give no indication that transferFrom is not implemented in the token and the fallback function will be called instead silently, see: https://github.com/OpenZeppelin/openzeppelin-solidity/issues/1769 371 | 372 | 111. be careful when calling other contracts and expecting them to fail on a problem because if the other contract does not implement the called function and implements a non-reverting fallback function then the transaction will be a success even though the desired function was not called 373 | 374 | 112. be careful when providing a public burn function to users to burn their tokens because there is a difference between sending to irrecoverable address and burning which decreases total supply because the first is not visible to the non-technical investors while the second one will change the token total supply on coinmarketcap which might cause undesired reaction from non-technical investors who follow the token in coinmarketcap and similar tools. Another difference is that discussions about the retrieval of locked tokens refer more to tokens sent to invalid address than to burned tokens, which shows that sending tokens to invalid address may still legally make those tokens belong to their owner, see the discussion here: https://github.com/ethereum/EIPs/pull/867#issuecomment-365746101 375 | 376 | 113. use modifiers to make code cleaner and understandable (modifiers are macros compiled inline). cleaner and more readable code improves chances of discovering bugs earier and writing better and more secure code. 377 | 378 | 114. security tools and other useful tools to use to scan smart contracts and develop smart contracts (FIRST CHECK THAT SCANNERS DON'T HAVE DISTRIBUTION RIGHTS FOR THE CONTRACT CODE): 379 | 1. https://github.com/ConsenSys/mythril-classic 380 | 1. to run on windows 381 | 1. first install docker desktop app 382 | 2. if the contract is using solidity compiler 0.4.24 and contract name is DDD and it is located in C:\Users\user\Downloads\target.sol then run "docker run --rm -v C:\Users\user\Downloads:/Downloads mythril/myth -x /Downloads/target.sol:DDD -mether_thief --verbose-report --solv 0.4.24" 383 | 3. the -v command maps the folder on the left of ':' in host to the folder on the right of ':' inside the docker 384 | 4. the --rm command cleans the docker after finishing running the command so if want to run several related/dependent commands then omit -rm and add it only in the end for cleanup https://docs.docker.com/engine/reference/run/#clean-up---rm 385 | 2. note: after running it need to wait about 10-20 minutes for it to finish (it does not show any output in that time so be patient) so better idea is not to wait for it and to do something else while it is running 386 | 3. CONCLUSION: YES. it is good and should always use it to get general direction to existing vulnerabilities (it does not produce exact exploit but gives a direction if it finds a vulnerability) 387 | 2. http://remix.ethereum.org 388 | 1. compiling in remix perform static analysis and might detect bugs 389 | 2. CONCLUSION: YES. it should be used but most if not all of the warnings are false positives so not to waste too much time on them 390 | 3. https://github.com/crytic/slither 391 | 1. requires python 3.6 392 | 2. pip install slither-analyzer 393 | 3. download latest solc compiler version and put it in the PATH (or otherwise slither will throw "file not found" error) https://github.com/ethereum/solidity/releases 394 | 4. reopen cmd and run "slither contract_file_path_and_filename.sol" 395 | 5. CONCLUSION: YES. it is good and should always use it to detect small possible optimizations and fixes 396 | 4. https://github.com/crytic/eth-security-toolbox 397 | 1. very heavy and takes a lot of time to download 398 | 2. contains slither, echidna, manticore and some other tools 399 | 3. docker pull trailofbits/eth-security-toolbox (takes 10+ minutes) 400 | 4. docker run -it -v C:\Users\user\Downloads:/Downloads trailofbits/eth-security-toolbox (replace "user" with the windows user name) 401 | 5. slither /Downloads/contract.sol (where contract.sol is inside the windows user downloads folder) 402 | 6. echidna-test /Downloads/contract.sol ContractName 403 | 7. CONCLUSION: YES. the eth-security-toolbox is slow to download but convinient if many of the tools inside it are used 404 | 5. https://github.com/crytic/echidna 405 | 1. use using eth-security-toolbox docker 406 | 2. requires to write tests to make it work so it is not a drop in solution 407 | 3. CONCLUSION: NO. not so useful for a simple quick security check since it requires development 408 | 6. https://github.com/trailofbits/manticore 409 | 1. use using eth-security-toolbox docker 410 | 2. https://github.com/trailofbits/manticore/issues/1382 411 | 3. https://github.com/trailofbits/manticore/issues/1315 412 | 4. CONCLUSION: NO. has a lot of bugs making it unusable right now 413 | 7. solidity security vscode extension https://marketplace.visualstudio.com/items?itemName=tintinweb.solidity-visual-auditor 414 | 1. CONCLUSION: use during development to fix problems as they are typed into the code 415 | 8. https://github.com/melonproject/oyente 416 | 1. https://github.com/melonproject/oyente/issues/334 417 | 2. https://github.com/melonproject/oyente/issues/268 418 | 3. CONCLUSION: NO. outdated and deprecated and not maintained anymore 419 | 9. https://github.com/raineorshine/solgraph 420 | 1. does not support new solidity versions https://github.com/raineorshine/solgraph/issues/39 421 | 2. CONCLUSION: NO. outdated and deprecated and not maintained anymore 422 | 10. https://github.com/MAIAN-tool/MAIAN 423 | 1. CONCLUSION: NO. outdated and deprecated and not maintained anymore 424 | 11. https://github.com/quoscient/octopus 425 | 1. CONCLUSION: NO. not well documented and not actively developed 426 | 12. https://github.com/cleanunicorn/karl 427 | 1. CONCLUSION: NO. not actively developed and installation on windows doesn't even work. it just runs mithril on deployed contracts so if the goal is to analyze your contract then better run mithril directly 428 | 13. https://github.com/ConsenSys/surya 429 | 1. npm install -g surya 430 | 2. "surya describe contract.sol" quickly displays a summary of the functions and contracts in the file 431 | 3. "surya graph contract.sol > dot -Tpng > contract.png" creates contract calls graph (dot tool is available here: https://graphviz.gitlab.io) 432 | 4. graph creation does not work https://github.com/ConsenSys/surya/issues/76 433 | 5. CONCLUSION: YES. can be good for general contract analysis, can help notice problems but does not provide vulnerabilities information 434 | 14. SECBIT Solidity Static Analyzer 435 | 1. https://github.com/sec-bit/adelaide/blob/secbit-ssae/README.secbit.md 436 | 2. available as vscode extension: https://github.com/sec-bit/vscode-secbit-ssae 437 | 3. https://marketplace.visualstudio.com/items?itemName=SECBIT.vscode-secbit-ssae 438 | 4. CONCLUSION: NO. does not work and is not actively developed or maintained 439 | 15. https://github.com/b-mueller/scrooge-mcetherface 440 | 1. ONLY RUN ON TEST ENVIRONMENT 441 | 2. doesn't have a docker and uses mithril which is not compatible with windows so easiest way to install is in case a docker is installer such as the eth-security-toolbox docker then run: 442 | 1. if container is running 443 | 1. "docker ps" 444 | 2. copy the CONTAINER ID of the ubuntu docker instance 445 | 3. "docker attach {container-id}" 446 | 2. if container is not running (or running not as root then "exit" and run this to start as root) 447 | 1. docker run -u 0 -v C:\Users\user\Downloads:/Downloads -it trailofbits/eth-security-toolbox 448 | 3. then run installation steps in that shell https://github.com/b-mueller/scrooge-mcetherface#installation 449 | 3. CONCLUSION: NO. not actively developed or maintained or supported and installation on windows doesn't work. it just runs mithril on deployed contracts so if the goal is to analyze your contract then better run mithril directly 450 | 16. https://github.com/protofire/solhint 451 | 1. npm install -g solhint 452 | 2. solhint init-config 453 | 3. solhint contract.sol 454 | 4. CONCLUSIONS: YES. useful to get formatting tips but doesn't give security tips 455 | 17. https://github.com/duaraghav8/Ethlint 456 | 1. npm install -g ethlint 457 | 2. solium --init 458 | 3. solium -f contract.sol 459 | 4. CONCLUSION: YES. useful to get suggestions on both formatting and coding and security 460 | 18. https://github.com/smartdec/smartcheck 461 | 1. npm install @smartdec/smartcheck -g 462 | 2. smartcheck -p contract.sol 463 | 3. can run automatically using https://tool.smartdec.net/ 464 | 4. CONCLUSION: YES. gives security suggestions which are 90%-100% false positives so use it but reverify the suggestions. dont use the command line tool because it is unclear, only use the online interface. 465 | 19. https://github.com/eth-sri/securify https://securify.chainsecurity.com/ 466 | 1. CONCLUSION: NO. does not work. normal and docker installations fail and when attempting to use their website to scan either pasted code or github repository then it is stuck in infinite 404 XHR errors until finally displays "bad gateway" error 467 | 20. https://github.com/tagomaru/truffle-sca2t 468 | 1. basically only integrates running mythx using truffle run mythx command 469 | 2. CONCLUSION: NO. should prefer to use mythx official integration (truffle-security npm package) which is officially supported and more actively developed 470 | 21. https://github.com/rajeevgopalakrishna/Solstice 471 | 1. https://medium.com/@rajeevgopalakrishna/solstice-solidity-security-tool-for-investigative-contract-examination-1fafda26d038 472 | 2. CONCLUSION: NO. official installation steps give syntax error and it is not actively developed or maintained 473 | 22. mythx + mythos + official truffle integration 474 | 1. npm install -g truffle-security 475 | 2. truffle run verify 476 | 3. https://github.com/ConsenSys/truffle-security 477 | 4. https://docs.mythx.io/en/latest/tooling/truffle.html 478 | 5. https://medium.com/consensys-diligence/mythx-and-truffle-security-painless-smart-contract-security-testing-6d0fe5e938da 479 | 6. https://github.com/cleanunicorn/mythos 480 | 7. https://docs.mythx.io/en/latest/tooling/mythos.html 481 | 8. basically mythx is a server side api and mythos and truffle-security and other tools are just client side tools integrating with mythx api so doesn't matter which to use. 482 | 9. CONCLUSION: YES. using truffle-security produced no output so used mythos instead and it performed security analysis as desired. should use it always to get security analysis tips 483 | 23. https://github.com/cgewecke/eth-gas-reporter 484 | 1. if solidity-coverage throws error about eth-gas-reporter not found then make sure everything is installed in same scope (installing eth-gas-reporter globally might solve the problem) 485 | 2. CONCLUSION: YES. useful to find problematic functions which take too much gas in unit testing of contracts 486 | 24. https://github.com/sc-forks/solidity-coverage 487 | 1. look at open zeppelin repository for coverage addition to truffle-config.json and for .solcover.js file contents but in .solcover.js only use norpc:true and change skipFiles to point to your truffle Migrations file and also add there your mockup contracts files 488 | 2. npm install --save-dev solidity-coverage 489 | 3. ./node_modules/.bin/solidity-coverage 490 | 4. node_modules\.bin\solidity-coverage 491 | 5. by default returns errors for solidity 0.5.0+ https://github.com/sc-forks/solidity-coverage/issues/316 492 | 1. open zeppelin installed https://github.com/rotcivegaf/solidity-coverage fork for solidity 0.5.0+ support so can do the same 493 | 2. but latest solidity-coverage development happens on this branch: https://github.com/sc-forks/solidity-coverage/tree/leapdao 494 | 3. the active branch can be installed using: npm install --save-dev git://github.com/sc-forks/solidity-coverage#leapdao 495 | 6. following those intructions to run on windows: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#running-on-windows 496 | 1. run "node_modules\.bin\testrpc-sc -p 8555" in another terminal before running the coverage 497 | 7. if get "Returned error: Exceeds block gas limit" error then delete gas, gasPrice configs from coverage config in truffle-config.json 498 | 8. if get "invalid opcode" errors then better not to run testrpc-sc and instead use ganache-cli and change truffle-config.json coverage port to 8454 ganache cli port https://ethereum.stackexchange.com/questions/69866/solc-error-invalid-opcode-but-works-in-truffle 499 | 1. UPDATE: using ganache-cli makes other errors happen and does not allow to get coverage report so the better solution is to update solidity-coverage to the active branch as described above 500 | 9. if get "base fee exceeds gas limit" error then in truffle-config.json increase or delete gas config from coverage network config 501 | 10. if get "out of gas" errors (because instrumentation of contracts makes them too big) then 502 | 1. add "--allowUnlimitedContractSize" parameter to the testchain execution to allow contracts above 24KB to be deployed (otherwise there is an out of gas error even though the reason is the size and not gas https://github.com/ethereum/EIPs/blob/master/EIPS/eip-170.md) 503 | 2. increase gas parameter of coverage network config in truffle-config.json to 0xfffffffffff (what is sent to the blockchain) AND increase ganache-cli gas limit to 0xfffffffffff (default is around 6.7 million) using -l parameter (what is supported in the blockchain): "ganache-cli -l 0xfffffffffff" 504 | 11. creates very helpful instanbul html reports which can quickly help add the missing test cases 505 | 12. CONCLUSION: YES. might be hard to make it work but it is a MUST HAVE tool to use to improve the testing coverage and after all configurations being set well it works as desired 506 | 507 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Use with the GNU Affero General Public License. 553 | 554 | Notwithstanding any other provision of this License, you have 555 | permission to link or combine any covered work with a work licensed 556 | under version 3 of the GNU Affero General Public License into a single 557 | combined work, and to convey the resulting work. The terms of this 558 | License will continue to apply to the part which is the covered work, 559 | but the special requirements of the GNU Affero General Public License, 560 | section 13, concerning interaction through a network will apply to the 561 | combination as such. 562 | 563 | 14. Revised Versions of this License. 564 | 565 | The Free Software Foundation may publish revised and/or new versions of 566 | the GNU General Public License from time to time. Such new versions will 567 | be similar in spirit to the present version, but may differ in detail to 568 | address new problems or concerns. 569 | 570 | Each version is given a distinguishing version number. If the 571 | Program specifies that a certain numbered version of the GNU General 572 | Public License "or any later version" applies to it, you have the 573 | option of following the terms and conditions either of that numbered 574 | version or of any later version published by the Free Software 575 | Foundation. If the Program does not specify a version number of the 576 | GNU General Public License, you may choose any version ever published 577 | by the Free Software Foundation. 578 | 579 | If the Program specifies that a proxy can decide which future 580 | versions of the GNU General Public License can be used, that proxy's 581 | public statement of acceptance of a version permanently authorizes you 582 | to choose that version for the Program. 583 | 584 | Later license versions may give you additional or different 585 | permissions. However, no additional obligations are imposed on any 586 | author or copyright holder as a result of your choosing to follow a 587 | later version. 588 | 589 | 15. Disclaimer of Warranty. 590 | 591 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 592 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 593 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 594 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 595 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 596 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 597 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 598 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 599 | 600 | 16. Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # KnowledgeLists 2 | Contains lists of things to know/remember in different topics. 3 | 4 | 1. Ethereum smart contracts security recommendations and best practices: https://github.com/guylando/KnowledgeLists/blob/master/EthereumSmartContracts.md 5 | , it was used and created during the creation of the BOK token smart contract. See SafeUpgradeableTokenERC20 contract implementation here: https://github.com/guylando/EthereumSmartContracts 6 | 7 | 2. Many information security lists which I will later move to this github repository appear in my blog here: https://secinfodb.wordpress.com/ 8 | --------------------------------------------------------------------------------