Questions tagged [security]
Questions relating to application security, safety, trust, and attacks against the Ethereum software stack and blockchain system.
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How can I securely generate a random number in my smart contract?
If I am writing a smart contract for some kind of (gambling) game, how can I generate a random number securely? What are the best practises and security trade-offs to be aware of?
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I got scammed or suspect scam on Ethereum. What to do?
This is a general question and answer on ethereum.stackexchange.com to all "I got scammed, please help" posts.
This applies to you if you think:
You have been scammed
You think something ...
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answers
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What number of confirmations is considered secure in Ethereum?
In Bitcoin, 6 confirmations are considered secure (very low probability of transaction/block reversal).
What is the current number in Ethereum?
eth♦
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<address>.send vs <address>.transfer best practice usage?
I noticed that address's offer two member functions that perform the transfer of ether to the specified address. send returns false upon failure and transfer raises an exception. In the Solidity ...
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How can I make new account by JSON-RPC?
I'd like to make new account by JSON-RPC.I've checked the wiki of Ethereum, however I could not find out how to do that.
I've found call existed accounts, but it isn't what I want.
eth_accounts
...
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3
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How do gas refunds work?
Gas refunds are provided when clearing storage or calling SELFDESTRUCT on contracts.
The Yellow Paper mentions that refunds are "being capped up to a maximum of half...". What exactly is ...
eth♦
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votes
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Why can't contracts make API calls?
The model that contracts can only accept and process data, instead of also being able to retrieve data from the Internet, seems limiting (even if not, it's less direct).
If a concern is that data or ...
eth♦
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Is each Ethereum address shared by (theoretically) 2 ** 96 private keys?
Summary
This is an extended question to How are ethereum addresses generated?.
In Ethereum, a private key is 256-bit long, but an address is only 160-bit long. By "Pigeonhole Principle", it ...
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How to reduce the chances of your Ethereum wallet getting hacked?
Summary
The hack that occurred on May 12 2016 to steal 7,218 ethers from Patrick only affects miners where:
Incoming RPC connections from the Internet on TCP port 8545 are forwarded to the machine ...
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What is a recursive calling vulnerability?
What is a recursive calling vulnerability exactly?
When creating smart contracts, DAOs or DAPPs, what measures can I take to ensure I am not vulnerable?
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Can a contract safely rely on block.timestamp?
How safe is it to use block.timestamp as contract expiration time? If a miner provides an incorrect timestamp in a block header, how much can it be off before it is rejected by other nodes? Is there a ...
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When can BLOCKHASH be safely used for a random number? When would it be unsafe?
I've seen more complicated ways for a contract to generate a random number. But the Ethereum Yellow Paper itself suggests a "trivial solution" using the BLOCKHASH opcode (see below, bold is mine).
...
eth♦
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2
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Ethereum smart contract security checklist
Is there a tool, checklist of methodology to help reviewing smart contract security?
E.g. for each of function you review
Is there re-entry possibility and how it behaves on re-entry
How it behaves ...
- 21.7k
25
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1
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What if I had the private key that had the public address of a contract?
Could I spend the money a contract owns if I had the private key that goes to the public address that a contract resides at? (I realize that I'd have a better chance of being struck by lightning ...
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Account uniqueness guaranteed?
When we create an account in the Ethereum main network, how does the protocol guarantee the unique address of an account? Since even if we are not connected to the network we can create an account, is ...
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What are effective techniques to encrypt/decrypt data stored in a smart contract?
Rather than sending and storing plain text in a smart contract, the use case objective is to encrypt first and then subsequently access the data and decrypt at the point of use.
What is the most ...
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Is transfer() still safe after the Istanbul update?
In other words, is using transfer() safe?
function transfer(address contractB) public
{
contractB.transfer(1000);
//balances[msg.sender] -= 1000;
}
How about using call.gas?
function ...
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11
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1
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Can I unlock an account using JSON-RPC?
The only way I can work with ETH is through --rpc mode. Normally I would prefer to use the Python interface.
But I found myself in a situation where the RPC is very limited. For example, I can't ...
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How can I verify that a contract on the blockchain matches the source code?
Given the (Solidity) source code of a smart contract, is there a way to deterministically compile the code and compare it with the code on the blockchain? I want to verify that the contract does what ...
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TheDAO hack FAQ: How did the attack happen on 17 June 2016?
Can anyone explain that how the DAO attack happened? Vitalik Buterin explained here that it was performed by splitting a DAO from the main DAO but calling the split function recursively.
We know that ...
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1
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Why isn't fast sync the default?
As I understand, fast sync has all the security guarantees of a full sync, but is faster. Is that correct? If so, why isn't fast sync the default?
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Solidity functions - private visibility
Is the following function parameter (string name) only visible to the owner contract itself?
function myFunction(string name) private returns (bool)
{
return true;
}
So nobody can read / see ...
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How does the Ethereum ETH accounting system work and prevent double-spends?
In Bitcoin, the BTC accounting system is based on UTXOs (Unspent Transaction Outputs), which prevents the same BTC from being spent multiple times. I heard that Ethereum has a simpler account balance ...
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Is there any safe way to send money from a cold wallet, using an untrusted computer?
You have 2 computers. One is 100% offline and, thus, trusted. Other is online. Private keys are stored on the offline computer and the online computer has no access to it. Is there any way to sign a ...
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During a 51% attack, What Can the Attacker Actually Accomplish?
During an attack on the network, where the attacker has more than 51% of hashing power (or the equivalent of Ether in PoS), what can the attacker do and not do to the chain and the contracts on it?
...
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How many ethers have been drained through the recursive call attacks on The DAO?
The recursive call attacks on The DAO have now stopped as there are no more ethers in The DAO account.
What are the amounts and percentages that can be attributed to the hostile and friendly attacks, ...
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5
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How will regular users be able to use dApps without buying ether?
Requiring users to get ether before they can use a dApp, is too much of a barrier for any kind of mainstream adoption. If dApps offer free ether in a naive way, they can be attacked by Sybils where a ...
eth♦
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Why were empty accounts allowed to be on the blockchain?
It's hard to see what the benefits of allowing empty accounts to be on the blockchain are. This was a known subtlety (see "note: there is a difference between zero-balance and nonexistent") and ...
eth♦
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How to unlock accounts programmatically after the node has started?
Is there any way of just unlocking accounts without opening the console with geth?
I'm writing some scripts to automate cluster generation and I wish I could just call geth to unlocking some accounts ...
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Is there anything stopping me from using the ethereum blockchain as data storage?
As I understand it, smart contracts are currently immortal by default. Does this mean that I could create a contract that happened to contain an encoded form of baby photos and have it stored forever? ...
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Is it safe to reuse Ether addresses?
I believe it's viewed as unsafe in Bitcoin because of the way transactions are signed. Is this also true for Ether addresses?
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How to validate a private key?
I could not find any library that, given an hex value, returns true if the given string is a valid ether private key.
Any hints?
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What happens if transaction runs out of gas before transaction completes?
As gas cost can only be estimated until the transaction is executed against the actual contract state at the time of execution on the blockchain, what happens if transaction runs out of gas before the ...
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How many The DAO recursive call vulnerability attacks have occurred to date?
The first identified The DAO recursive call vulnerability attack occurred on 17 June 2016, with the accounts identified in Which accounts are involved in mounting the recursive call vulnerability ...
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votes
1
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State only node
Is it possible for the network clients to just keep the latest network state (without keeping track of the past transactions) while not harming the network security? That is, is it really needed to ...
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Is it possible to overflow uints?
The Ethereum token tutorial has a check for a uint256 overflow.
function transfer(address _to, uint256 _value) {
/* Check if sender has balance and for overflows */
if (balanceOf[msg.sender] ...
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What Hierarchical Deterministic (HD) wallets are available for Ethereum?
A Hierarchical Deterministic (HD) wallet has some nice features such as easier backup (instead of needing to backup multiple keystore files and the passwords for each of them).
Are there any ...
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"potential rewrite attack" message on Geth
When I was sending Ether using Mist I got the following message on Geth.
I0528 18:34:57.312997 core/blockchain.go:959] imported 1 block(s) (0 queued 0 ignored) including 3 txs in 19.344963ms. #...
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What data will zk-SNARKs protect?
Implementing zk-SNARKs is planned in Ethereum roadmap, what data will be obfuscated?
transaction sender and receiver?
data in transactions?
data stored in contracts?
variables and methods in ...
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How does a fallback function rejecting ether work?
A contract in Solidity can have a fallback function like:
// This contract rejects any Ether sent to it. It is good
// practise to include such a function for every contract
// in order not to loose ...
eth♦
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Is there a way to generate ethereum paper wallets?
Is it possible to store ether on paper wallets or generate printable private keys offline somehow?
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Is Solidity block.number more secure than timestamp?
In Solidity, some properties such as block.timestamp are attackable by miners and are not (strongly) protected by the protocol. How about block.number, could a miner introduce a randomly high number?
...
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How does Oraclize handle the TLSnotary secret?
Oraclize claims to offer a provably honest secure retrieval of a webpage by taking advantage of TLSnotary (a service that allows an auditor to verify if a specific web page was accurately retrieved)
...
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How to steal eth using delegatecall and selfdestruct
This documentation says
Even if a contract’s code does not contain a call to selfdestruct, it can still perform that operation using delegatecall or callcode.
This worries me.
I've created ...
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How does the stack depth attack make a send() silently fail?
From a blogpost on security from Christian Reitwiessner:
Because of the maximal stack depth of 1024 the new bidder can always increase the stack size to 1023 and then call bid() which will cause the ...
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What about illegal smart contracts?
Trying to get a friend excited about smart contracts I referred him to an ethereum pyramid scheme as an easy to understand example but he only pointed out that all pyramid schemes are illegal. How ...
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Flash loan security considerations and attacks
What do developers need to be aware of to make their contracts and systems safe against flash loans?
What do they have to think about and protect against?
eth♦
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Is sending some datas in the data field safe?
An airdrop ask to send it 0ETH with 150000 GAS and some datas in DATA field.
Is it safe?
What could be the aim of this transaction?
Thanks.
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How do I "Add Data" to a send transaction in Solidity
In myetherwallet, there is an +Advanced: Add Data Section where I can add data to the transaction.
How can I add this same data in a transaction I make in Solidity?
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Honest lottery winner generation - pseudo random number obtaining
Suppose I would like to organize a honest lottery and prevent cheating when we need to find a winner. I known problem of random number in the known network arises.
I would like to try the following ...
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