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21
votes
4answers
9k views

How can the transaction status from a thrown error be detected when gas can be exactly the same as the gasUsed for a successful transaction?

This question arose from answering Transaction Status. In the following example, I am sending gas of 21,000 (the amount required for a regular transaction). In this situation gas == gasUsed, and so ...
21
votes
8answers
33k views

How do I get the raw private key from my Mist keystore file?

I use the Mist wallet. I would like to know: How I can get the private key of my account. How I can use this private key to sign messages.
15
votes
2answers
1k views

How to get values returned by non constant transaction functions?

As per my understanding when I invoke a constant function without a transaction in a contract and if the function returns some result I am able to get it in EthereumJ or Go-Ethereum, But when a ...
60
votes
2answers
19k views

Difference between CALL, CALLCODE and DELEGATECALL

CALL and CALLCODE take the same number of operands (in the execution stack). For the exception flag being pushed on top of the stack: 0 means exception, 1 means successful execution. CALL is easy to ...
56
votes
2answers
29k views

What does each genesis.json parameter mean?

I'm trying to setup genesis.json for my private network. What does each parameter mean and what value can I set in genesis.json? nonce: any data? timestamp: any time? parentHash: any hash? extraData: ...
39
votes
2answers
27k views

How to select a network id or is there a list of network ids?

We're starting a new open network based on the Ethereum protocol. The question is how to allocate a network id for the new network. In Ethereum we have main net, four test networks, classic with test ...
14
votes
1answer
5k views

What Ethereum blockchain explorers exist?

What blockchain explorers exist and What special features do they have? Are they open-source? How reliable are they (approximate uptime in %)? Is there a testnet version?
30
votes
2answers
19k views

What is nonce in Ethereum? How does it prevent double spending?

recently I got fascinated by blockchain, and started learning Ethereum. I came across the concept of the nonce in Ethereum. After researching I found out that nonce is used for two purposes. a. To ...
22
votes
1answer
9k views

Deploy contract from contract in Solidity

It's a common pattern to use a hub/factory contract to create multiple instances of a standard contract. It's also common to require a way to enumerate the addresses of the created contracts. Is ...
25
votes
4answers
7k views

What public test-networks and faucets exist?

What public test-networks exist and what are their conditions? What are the connection data? How often (if so) are they reset? Does a public faucet exist for this test network? Does a block explorer ...
15
votes
2answers
11k views

How do I get a refund for the amount I paid in excess of 1 ether to 100 The DAO tokens

Anyone who bought DAOs in the last two weeks of The DAO crowdfunding phase paid more than 1 ether (ETH) per 100 The DAO tokens (DAO). The ETH amount in excess of 1 ETH per 100 DAOs was stored in The ...
20
votes
2answers
3k views

Private info in an Ethereum smart contract

Is there any way to store info on a smart contract, and keep it a secret? If a contract has a state variable that is not public like: contract foo{ uint public publicVariable; uint notPublic;...
40
votes
3answers
12k views

What are the pros and cons of Ethereum balances vs. UTXOs?

Ethereum has a simpler model by not having UTXOs (Unspent Transaction Outputs) like Bitcoin. What does Ethereum "give up" by not having UTXOs, and what does it gain?
49
votes
2answers
46k views

How do I backup my ether accounts?

I want to backup my accounts onto a USB or other external device for safe-keeping. How can I do that?
25
votes
4answers
31k views

How to call my contract's function using sendTransaction

This may be a very basic question, I don't know why but I am unable to find correct solution to how can I call my contract's method using sendTransaction. I have a transfer(address, uint256) function ...
15
votes
1answer
2k views

How much computation can be done in a fallback function?

Simply sending Ether to a contract, will run the contract's code. In Solidity, this code maps to what it calls the fallback function. How much work can be done in a fallback function?
26
votes
4answers
12k views

How can I represent decimal values in Solidity?

I just started writing some solidity and I noticed that there are no decimal values such as double or float. What do you guys do when you need to return send to a wallet let's say 1.57 ether? Or when ...
24
votes
1answer
5k views

What is the “difficulty bomb” and what is the goal of it?

The difficulty bomb is related to the switch to proof of stake. How does it work exactly and why is it going to help to switch to proof of stake?
48
votes
3answers
21k views

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 ...
63
votes
2answers
21k views

Solidity: What is the difference between `view` and `constant`?

Solidity 0.4.16 introduced the view and constant function modifiers. The documentation says: constant for functions: Same as view. Does this mean view is just an alias for constant? If so, why do ...
37
votes
2answers
9k views

Is there a (theoretical) limit for amount of data that a contract can store?

Is there a theoretical limit to the amount of data that one contract can store while running in a private net in which gas is not a concern? Context: In a financial Dapp which is to replace global ...
16
votes
1answer
6k views

How much does it cost to use a contract?

Still new to ethereum and would like to know the price for a contract.
17
votes
1answer
1k views

What is the order and concurrency behavior of multiple calls to a contract in a single transaction?

Suppose a contract has three call APIs that have side effects. What's the behavior if I try to: Call all three APIs from one address (i.e. issue three transactions if from nodejs). Are all three ...
125
votes
5answers
42k views

Why does Ethereum plan to move to Proof of Stake?

The initial version of Ethereum (Frontier) uses a Proof of Work based consensus algorithm, but I see that there are plans to implement a Proof of Stake based consensus algorithm called "Casper" in a ...
32
votes
1answer
26k views

Transaction Status

A very elementary question, how do I get a transaction status after firing the transaction? I mean suppose I do a sendTransaction where I transfer some amount of ether from 1 account to other, how can ...
29
votes
3answers
13k views

How to create a Dapp from scratch on Ethereum?

Let's say we have someone who knows about blockchain but who doesn't have any background in blockchain-based application. That person wants to code an ethereum-based Dapp (decentralized application) ...
48
votes
3answers
8k views

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?
43
votes
4answers
20k views

What exactly is an Ethereum client and what clients are there?

What exactly is an Ethereum client? Is it a full network node that can post transactions to the blockchain (if that is the correct lingo?) or could it also be a light JS client that connects from a ...
53
votes
5answers
13k views

How can you decompile a smart contract?

On the blockchain I can inspect the code of a contract, and see the EVM opcodes. Is there a way to decompile this and convert it back to (Solidity) source code?
31
votes
3answers
8k views

Difference between Memory and Storage?

What is the difference between Memory and Storage ? From both the EVM point of view and the contract design one. Thanks!
27
votes
5answers
9k views

How can I sign a piece of data with the private key of an Ethereum address?

I would like to use the key pair of one of my Ethereum accounts to sign a piece of data. How can this be done?
41
votes
4answers
17k views

What is the zero, empty or null value of a struct?

If I have a mapping of string => custom defined struct, how do I check if a value is defined in the mapping? The docs state that "every possible key exists and is mapped to a value whose byte-...
33
votes
3answers
37k views

How do miners profit post-PoS, if at all, how will new miners get their start, and who will execute the EVM byte code (and why)?

I've been following the release of Casper/PoS closely, and I'm curious about a few details. How will miners make money (even if GPUs are less valuable)? Are spare compute resources (say RAM, CPU) ...
21
votes
2answers
4k views

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 ...
18
votes
4answers
13k views

workflow on signing a string with private key, followed by signature verification with public key

I know this question has been asked and answered, but while trying to get everything to work, I've come across some problems. This is what I'm trying to do: 1. take a target string 'Schoolbus' 2. ...
38
votes
3answers
14k views

How do oracle services work under the hood?

I have read many questions about oracle services, but I do not understand how they work. Often I read answers like this: https://ethereum.stackexchange.com/a/9825/5892 Smart contract can not ...
47
votes
3answers
12k views

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 ...
38
votes
4answers
128k views

Is CPU mining even worth the Ether?

I would like to start mining Ether, but my GPU isn't the greatest and I don't really want to spend the money on a dedicated rig. Is mining from my CPU (in a Linux environment) still worth the Ether? ...
30
votes
3answers
5k views

What is a replay attack?

During the launch of the frontier network, users were cautioned not to reuse keys from the Olympic testnet in order to prevent "replay attacks". What is a replay attack, and why would re-using a key ...
23
votes
2answers
78k views

What's the best hardware for Mining Ether?

As my title says, I am a complete newbie to the Ethereum Project, but not to the cryptography in general. Although this will be the first time I will consider investing in the mining process. And I ...
26
votes
4answers
6k views

Does every node execute the contract code for each transaction?

This question was asked on Reddit a while ago: When a node sends a transaction to the network and has the receiver as a contract, does every node execute the contract bytecode with the inputs to ...
18
votes
2answers
6k views

What are the peer discovery mechanisms involved in Ethereum?

There are several implementations of Ethereum clients. How do these clients find each other? What are the algorithms and peer-to-peer protocols involved in this peer discovery process?
16
votes
5answers
48k views

How can I recover or reset a lost wallet password?

Let's say that a user has lost or forgotten their password. Is there a way to reset the password or recover it?
9
votes
2answers
2k views

Unable to define greeterContract in the Greeter tutorial. Breaking change in Solidity 0.4.9!

I was following the Greeter tutorial on Go Ethereum wiki and got stuck on the "var greeterContract = web3.eth.contract(greeterCompiled.greeter.info.abiDefinition)" phase returning TypeError: Cannot ...
16
votes
2answers
4k views

Can a contract listen to events of another contract?

I read that to listen to events you need to use web3.js. Are there other ways of doing it? Can a contract even somehow listen to events of another contract? Thanks!
12
votes
1answer
4k views

Peer discovery not working on private network

I'm running 3 nodes with the following command: geth --verbosity 4 --autodag --nat any --genesis /opt/blockchain/genesis.json \ --datadir /opt/blockchain/data --networkid 4828 --port 30303 --rpc ...
8
votes
5answers
9k views

Sent ETH to my Wallet, but it did not show up

Note: This question was initially asked for Mist, but is in general also true for all other wallets like Ethereum Wallet, Etherwall, Parity, Harmony, etc. I sent ETH from MyEtherWallet to my Mist ...
125
votes
1answer
47k views

What is Swarm and what is it used for?

What is Swarm and what is it used for? And what is Swarm's relationship with Whisper?
112
votes
5answers
128k views

What is a DApp?

There are new terms in Ethereum like smart contract. What is a DApp and how is it different from smart contracts?
33
votes
6answers
15k views

How do I parse the transaction receipt log with web3.js?

The event parser in web3 provides a nice parsing functionality for events, and I use it for logging all events to a file, but it's very difficult to use for looking at individual events for a ...

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