Questions tagged [consensus]

The process used by mutually untrusting users to agree on the validation and execution of transactions and smart contracts.

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131
votes
5answers
44k 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 ...
86
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3answers
30k views

What is an uncle/ommer block?

The Ethereum blockchain is described as containing "ommer" blocks, usually called "uncle" blocks by the general public. What is an ommer/uncle block, and why are they needed?
70
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What's the difference between proof of stake and proof of work?

The Ethereum frontier network currently uses a proof of work (PoW) consensus algorithm, while a future version of the network plans to utilise a proof of stake (PoS) algorithm instead. What's the ...
67
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1answer
11k views

Why is the average block time 17 seconds?

The network stats show a constant average blocktime of around 17 seconds. Whenever you check it is around 16~18 seconds. Reading the blog post by vitalik buterin it states the block time should be 12 ...
53
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4answers
32k views

What proof of work function does Ethereum use?

The Ethereum frontier network currently uses a proof of work (PoW) based consensus algorithm. But which specific PoW function does that algorithm use, and why was it chosen?
48
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4answers
27k 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 ...
40
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3answers
16k views

How does the Casper proof of stake algorithm work?

Ethereum plans to move to the Casper proof of stake algorithm in a future version of the network. What are the details of that algorithm, and how does it compare to previous Proof of Stake consensus ...
36
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4answers
18k views

What happens when a transaction nonce is too high?

From Design Rationale: One weakness of the account paradigm is that in order to prevent replay attacks, every transaction must have a "nonce", such that the account keeps track of the nonces used ...
34
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3answers
5k views

What was the reason to invent the EVM?

What was the reason to invent the Ethereum Virtual Machine (EVM)? Why not use an existing virtual machine like the Java-VM. The big advantage would be that the existing toolsets for Java development ...
28
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4answers
9k 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 ...
27
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3answers
4k views

Is Ethereum secure against an attack by quantum computers?

Does Ethereum implement Post-quantum cryptography? Or will the network break once a malicious actor gains control of an effective quantum computer?
18
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2answers
3k views

What is casper? [duplicate]

I see that Vitalik and Vlad are working on Casper. As far as I understand, casper is the new POS mining algorithm. Why is it better than bitcoin's POW? I understand it's environmentally friendly, ...
17
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2answers
2k views

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? ...
15
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1answer
8k views

How many transactions per second can Ethereum currently handle? What changes will allow the network to be able to handle more? [duplicate]

I've been searching for a more precise answer to this question, but I've seen a lot of conflicting information stating that Ethereum can currently handle anywhere from 12-45 transactions per second. ...
14
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2answers
5k views

QuorumChain Consensus vs Raft Consensus vs Istanbul consensus quorum

I am reading about Quorum which is an Ethereum-based distributed ledger protocol with transaction/contract privacy and new consensus mechanisms. I have read about QuorumChain consensus and Raft ...
13
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2answers
3k views

What does it mean to "seal a block"?

In both the Ethereum chain specification format and in Parity's documents on private chains, you see the term seal a block. What exactly does that term mean? How is it different than mining a block?...
12
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3answers
2k views

Smart contract consensus for dummies

I've read a few other questions/answers on smart contract consensus by nodes in the network, but I still don't understand the steps. Here's how I picture it: Two parties might agree upon a smart ...
11
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3answers
2k views

What are the major risks of Ethereum moving to Proof of Stake?

There has been discussion about the motivations and benefits of moving to Proof of Stake. For a risk-benefit analysis of moving to Proof of Stake, what are the major risks?
11
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2answers
206 views

How dependent is the ethereum client on the router and DNS being trusted?

Another way to put it: what is the root of trust for a full client on a network that has a potentially untrusted (or "owned") router+DNS? As I was going through the ethereum wiki semi-randomly, I ...
9
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2answers
469 views

How can I compare two consensus protocols?

There are a large number of competing consensus protocols in the blockchain space today. How can I compare them to each other in an objective way?
9
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1answer
393 views

When there is an unexpected hardfork, what is the procedure taken by the core team?

Imagine Ethereum had a hardfork like this one that Bitcoin experienced. Ethereum can learn from this and can be prepared to be more efficient during the crisis, minimize panic, minimize other ...
9
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1answer
351 views

Can a smart contract be validated only by a specific selected node

Is it possible to direct a transaction to a validating node such that - while other nodes receive the broadcast, only the selected node can validate the transaction and the others simply ignore it? ...
9
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1answer
283 views

How is "by-block consensus" different from " by-chain consensus"?

I see Vlad Zamfir was able to demonstrate by-block consensus has great merit to Vitalik. Is it better than by-chain consensus? What are the risks associated with developing by-block consensus into ...
8
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2answers
5k views

What is GHOST and what is its relationship to Frontier and Casper?

As high-level as possible without losing important meaning, what's the intuition behind GHOST? How is it currently implemented in Frontier? What will be different with GHOST in Casper?
8
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2answers
651 views

How does betting on a block work in Casper?

Betting on a block is betting money that effectively says something like: "I believe that this block has at least a 60% chance of being true." Q1. Once a bet is made, is it possible to change the ...
8
votes
1answer
349 views

What happened in the Ropsten hardfork from Byzantium to Constantinople?

What were the consensus issues during the Constantinople hardfork in the Ropsten testnet? One noted consensus issue is: geth and parity have been in noticeable disagreement regarding block ...
7
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4answers
657 views

What are the open issues with the Casper proof of stake algorithm?

Ethereum plans to move to the Casper proof of stake algorithm in a future release named Serenity. There's a comment that Casper's "basic mechanisms are fairly firmed up now". What are the details of ...
7
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1answer
3k views

Bitcoin : Ethereum :: Raft : Paxo

When we look at the earlier attempts to solve consensus problem in distributed systems, we encounter Raft and Paxo, are they analogous to what we see while comparing the technology behind Bitcoin vs ...
7
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2answers
609 views

How does the system enforce correct execution of smart contracts?

If I understand correctly, the smart contracts are run by the miners. What incentive do the miners have to execute the smart contracts correctly? What stops a malicious miner from changing the result, ...
7
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2answers
1k views

Smart contracts code: what are nodes in Ethereum actually agreeing upon during the consensus process?

When a contract is triggered, all nodes execute the code; where exactly does consensus come in? Are they agreeing upon the OUTPUT or just the code itself?
7
votes
1answer
175 views

How to propose future gas prices of OPCODES? [closed]

I'm concerned as to how are we going to reach consensus if new opcodes are to be included on the EVM or if we would like to update the cost of some opcodes. The gas price has been chosen arbitrarily ...
7
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2answers
508 views

Hyperledger Consensus protocol. [closed]

I'm soo deep inside the consensus protocols like PoW, PoS, PoA or other variants used on permissioned/private blockchains such as JPMorgan's Quorum (Based on Raft), Istambul etc.. But I've not ...
7
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2answers
4k views

What is the Ethereum Virtual Machine?

What is the Ethereum Virtual Machine? How does it contrast to the Ethereum World Computer? The description of the EVM tag says: EVM is the Ethereum Virtual Machine, the protected, distributed "...
7
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1answer
418 views

Who runs Plasma's side chains?

If I want to start a Plasma side chain for a project, do I need my own blockchain for it (with X amount of nodes etc) or is it run simply by those who participate in it? If it's run solely by its ...
7
votes
1answer
2k views

How to change the consensus algorithm in ethereum from PoW to PBFT?

https://github.com/ethereum/wiki/wiki/Consortium-Chain-Development I would like to use PBFT as the consensus mechanism in my locally deployed ethereum network. as the document specified above, we ...
7
votes
1answer
342 views

In Casper, how can a block be finalized if previous blocks are unconfirmed?

As explained in an Ethereum blog post, one consequence of consensus-by-bet is that: a block can remain unconfirmed even when blocks after that block are completely finalized. The given example ...
6
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3answers
2k views

What is the Oracle Problem definition exactly and briefly?

What is the Oracle Problem definition exactly and briefly? Does it mean "trusting on a centralized Oracle" ? Or "How to reach a consensus between a group of Oracles" ? Is the matter "centralization" ...
6
votes
1answer
695 views

How are contracts executed on nodes?

How are contracts executed on full nodes? Do they run one by one on first-in first-served basis, or simultaneously in the isolated environments? If they run in parallel, I guess it may exhaust the ...
6
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4answers
143 views

How does the process of executing code and consensus not yield thousands of the same transaction?

If execution is performed by every node on the network, how do you not end up with thousands of transactions transferring money (say a wager contract) multiple times? How does the network go from ALL ...
6
votes
1answer
1k views

What is the significance of uncle rate?

What is the significance of uncle rate? Some Ethereum sites show an uncle rate in decimal, another shows the uncle count per 25 blocks. If there are many or few uncles, how important is that to the ...
6
votes
2answers
1k views

What is the consensus mechanism used in Parity for 'Proof of Authority' chains?

The Ethcore Parity wiki states that it supports 'Proof of Authority Chains'. What distributed byzantine consensus mechanism is used?
6
votes
1answer
170 views

Incentive to vote early in Casper FFG protocol?

If I understand the Casper FFG protocol correctly, (1) all votes are public, and (2) the optimal voting strategy would be to observe other votes and vote accordingly (see this post, section "The ...
6
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0answers
151 views

Does everyone have to run all the contracts? [duplicate]

Does everyone have to run all the contracts or can nodes pick and choose what contracts they want to run? I'm still trying to wrap my head around how many nodes need to run a contract before I can ...
5
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3answers
1k views

What is consensus-by-bet?

So I'm reading up on Casper, and I see Consensus By Bet. How does it protect the network in a POS system?
5
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1answer
438 views

What is the proof that Mainnet can't be reset?

It has been argued that the Morden testnet can be reset any time. How can one verify that this is not possible with the mainnet?
5
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2answers
3k views

How does a Smart Contract know the gas/fees needed to execute a transaction?

I installed recently Solidity for Visual Studio and they have this Smart Contract sample there: contract Payout { address Victor; address Jim; address Kieren; mapping (address => uint) ...
5
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1answer
320 views

What is the longest fork that had occurred so far?

What is the longest fork that had occurred since the start of Frontier?
5
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1answer
2k views

Is "Proof-of-work" a subset of "Byzantine fault tolerance (BFT)"?

Can we say that Proof-of-work is a type of Byzantine fault tolerance (BFT) ? In other words, is PoW a subset of BFT ? Or they are two different categories? Please note that there is a similar ...
5
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1answer
168 views

How trustless and secure are Events?

How trustless and secure are Events? They are part of the consensus as they are generated out of a smart contract code. so in theory they are trustless and secure. But they are not stored on chain or ...
4
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2answers
217 views

Logic of Ethereum Consensus - Part 2

Consensus Logic with an example Person A generates a transaction to pass some ether to person B The transaction is submitted on the node Node then passes that unconfirmed transaction to ...

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