Questions tagged [consensus]

Questions about the consensus system of Bitcoin and the protocol rules that are consensus critical.

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54 views

How are malicious forks resolved?

I understand that forks are resolved by opting in for the eventual longest chain, preferring the chain with the longest POW. But everything I read on this suggests it's just random chance or that the ...
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49 views

Preventing secretly mined chains

In order to prevent attackers from secretly mining chains (which they could later publish to perform double-spending attacks), would it be possible to require some information to be included in the ...
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50 views

Why does the value range of outputs need to be restricted?

In the 'tx messages' section for protocol rules we have Each output value, as well as the total, must be in legal money range For each input, if the referenced output does not exist (e.g. never ...
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22 views

How does the blockchain prevent transaction based on outdated note

This question borders along the line of cryptography and distributed systems, but I guess I have a strong chance of getting an answer if asked here. So here goes: I understand that the blockchain is ...
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31 views

how is bitcoin network protect itself from malicious nodes? [duplicate]

Can someone explain how does Bitcoin network protect itself from malicious nodes? Lets say someone creates bitcoin core clone and they manipulate it to their need. For example could someone change ...
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Can cryptocurrencies like Bitcoin be turned into a censored payment system under that would be financial regulation framework creating soft forks? [closed]

It s well known mining pools as well as hashing power is centralized in countries where electricity is cheap and using mining farms rather belonging to at least medium sized companies than single hand ...
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571 views

How does the BTC protocol guarantee that a “main” blockchain emerges?

I'm reading up on the bitcoin/blockchain technology. Usually, the part about proof of work and how to create a block is well explained. However, what is never explained is how/why the communication of ...
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2answers
130 views

Will the 1MB block size increase in the future?

The current Bitcoin block size is 1MB and is generated every 10 minutes, therefore 7 transactions per second. If the use of Bitcoin increase in the future, is the 7 transactions per second going to be ...
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65 views

How does the blockchain know if its block hashes have been tampered?

I'm dealing with some problems to finally understand how implicit consensus works and I've come across with one question. Suppose the following: A malicious miner proposes the following block to be ...
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1answer
78 views

What is the difference between Consensus and Distributed Consensus?

This is more of a clarification than as a question. Since I didn't have the rep to post a comment in this question, I'm putting this itself as a question. Sources I've referred till now: A ...
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39 views

How is difficulty enforced in the bitcoin blockchain? [duplicate]

Is it through some sort of voluntary acceptance by miners or is it hardcoded into the bitcoin blockchain to not accept a block which doesn't achieve a given difficulty level?
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2k views

How do Bitcoin devs make sure that their modifications do not affect the consensus rules or the running network protocol?

I understand that Bitcoin consensus rules are enforced by every single node individually. However, most people run the default version of Bitcoin Core, which makes the implementations done by Bitcoin ...
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223 views

what if the timelock is in the past?

I just started learning about bitcoin scripting and wonder: what if the timelock in CLTV is in the past? what if the timelock in nLocktime is equal to 500.000?
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In blockchain, if no new members join the network can we prove that there will not be anymore forks before a certain point in history?

I would like to know if we can allow new members to join with the promise that they will not attempt to create a new fork however hard it may prove to be, before a certain point in history. To this ...
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31 views

Should a node follow the longest chain, or the chain with most work while syncing?

I'm reading mixed things online - some saying to follow the longest chain, and some say to follow the chain with the most work. But I'm not convinced of the former. If the node follows the longest ...
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CVE-2012-2459 , possible code and performance improvement, is my logic correct?

ok so, in my effort to create a fullnode from scratch both for learning purpose and need (not a topic for discussion, thanks), I was looking at the code that check Merkle Root to not be vulnerable to ...
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Why do we need 2F prepare certificates instead of just F+1 in PBFT?

I started reading PBFT and I could not understand: why do we need 2F prepare certificates? The client needs only F + 1 replies, not 2F, so why can't the same rule be applicable in the prepare phase of ...
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100 views

UTXO snapshots and history pruning

Is there a research, BIP proposal or simple discussion about possible improvement on the size required to run a full node and a way to shrink/prune the history of bitcoin and have fast sync? Let me ...
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1answer
61 views

What will happen when a collision in SHA256 be found?

Would the protocol migrate to another Hash Algorithm inmediatly? What would be the next? SHA3 or BLAKE 2?
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49 views

Some miners set the nVersion field of the block header to 0x8000004. What were they signalling for? Was this an error?

Some miners set the nVersion field of the block header to 0x8000004. What were they signalling for? Is this an error? I have been through a lot of the BIP documentations, but cannot seem to find any ...
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48 views

What was the first BIP9 block? Block 370,434 (0x20000007) or Block 398,364 (0x30000000)?

Block 370,434 (00100000000000000000000000000111) and (0x20000007) Yes: BIP9 says set top 3 bits to 001. No: BIP101 explicitly says set first, second, third and 30th bits to 1. No: No mention of BIP9 ...
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22 views

Which major/noteworthy BIPs, Soft-Forks and Hard Forks have there been since the Summer of 2017 (after SegWit/Bitcoin Cash)?

There are many lists of major forks however most of them end after SegWit. The full list of BIPs is extensive. Which noteworthy BIPs, Soft Forks and Hard Forks have there been since SegWit and Bitcoin ...
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1answer
38 views

How were miners supposed to signal support for BIP148?

Under BIP141 (SegWit), you could signal support by setting nVersion bit 1 equal to 1. BIP9 counted: 20000002 100000000000000000000000000010 20000012 100000000000000000000000010010 30000007 ...
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Vulnerability of Bitcoin Network

Hi all I was wondering if I am doin a wrong assumption here: Let's assume a dezentralized peer to peer network and the bitcoin protocol. If a full node changes a transaction within a block and then ...
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326 views

Who decides the block reward in Bitcoin?

I know that when a miner mines a block, he will be rewarded with some bitcoins. But who decides how much bitcoin he will get? If it is decided by all the miners (as they are the ones verifying ...
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114 views

BIP34, BIP66 and BIP65 should have been enforced at unique block heights. Why do different sources claim different block heights for enforcement?

Inconsistent Consensus/Activation of BIPs BIP34 Activated Block Height 227,835 (BitMEX Reference) Activated Block Height 227,930 (Bitcoin Developer Reference) Activated Block Height 227,931 (...
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When did BIP16 pass the 550/1000 threshold?

BIP16 says on 01 Feb 2012, if more than 550 out of the previous 1000 blocks include "/P2SH/" in the coinbase, then BIP16 will activate on 15 Feb 2012 (Source). BIP16 was later revised. On 15 Mar 2012,...
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1answer
45 views

How a transaction is permanently accepted by the blockchain?

If a miner A creates a block containing a transaction A and a miner B creates a block NOT containing the transaction A about at the same time, then some of the other miners will first receive the ...
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1answer
51 views

Can the forked be unforked?

So: BTC, BCH, BTG and BSV all trade at different prices/values. All have forked off from BTC and have different development teams, theories, practices, technology, etc. I noticed that when you look ...
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37 views

What are the script size limitations according to consensus rules and are they enforced on TestNet?

I'm trying to figure out the limitations that scripts have regarding their size, limits that would make a script invalid (ignoring standardness). According to this question and also these lines of ...
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1answer
151 views

How do miners communicate in Bitcoin/ Decentralized Network?

1.)If there is no central authority maintaining database how miners differentiate among other miners. 2.)Do they have there own database which have details(Mac/IP address) of neighbouring miners . 3....
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90 views

What is the benefit of having a fixed target block interval?

By design Bitcoin targets a block interval of 10 minutes. How does the blockchain benefit from maintaining a bounded block time?
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why bip 34 uses two step on MASF(Miner Activated Soft Fork)?

in bip 34, which change to bitcoin version 1 -> 2, uses two step for network's consensus. step 1. check if 750 of the last 1000 blocks are version 2 or greater. step 2. check if 950 of the last ...
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44 views

Mining process in a blockchain

Let's consider a blockchain. They mining nodes are listening to transactions and every one is building is own block. Due to latency and other issues, every miner is probably building a different block,...
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101 views

When exactly do the transactions get validated?

I have some gaps in my understanding to the life cycle of the transaction that I want someone to help me fill them specially with the validation. What I understand about the life cycle with my ...
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1answer
69 views

Was it always required for the Coinbase transaction to be the first transaction in a block?

The user tempo mentioned on another topic: "At least in the early protocol versions it was possible to put the coinbase transaction not on the top of the outputs." I have never heard about this ...
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510 views

Can a blockchain's transactions be reversed?

Blockchains are often described as 'immutable' (meaning the history cannot be rewritten after the fact), but is this really true? How easy is it to change the history? I have read about the Ethereum ...
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1answer
45 views

Could a malicious attacker subvert the Bitcoin network by failing to create a block?

I know its astronomically improbable, but say a malicious node "wins" the proof of work inherent to the Bitcoin protocol. If a malicious node simply waited indefinitely, or maliciously disconnected ...
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30 views

Can you call PoW 2f resilient?

Can you call PoW 2f resilient if all nodes would have same hash power? PoW is called eventually consistence. Even in an asynchronous network. The only attack possible is 51% attack. Further, there is ...
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32 views

Bitcoin consensus and server of miners

I know consensus is what 51% thinking.My questions is where miners communicated?On what server,what port??Where??The must push own api (copy of blocks) for thinking of consensus.So where BTC miners ...
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96 views

What is “consensus”?

I’m really struggling to get my head around a particular piece of lingo in the bitcoin/blockchain space, and would really appreciate if someone was able to give a bit of clarity. I have been doing a ...
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1answer
238 views

Difference between PoW and BFT

What is the difference PoW algorithms (as used in Bitcoind) and BFT (used for instance in Libra) ?
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44 views

How to detect a consensus is BFT or not? [closed]

Can we divide consensus algorithms into BFT (Byzantine Fault Tolerant) and non-BFT ? If so, How to detect a consensus is BFT or non-BFT ? Is there any non-BFT consensus algorithm example ?
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616 views

What is the difference between BFT and PBFT

What are the differences between BFT and PBFT? I want to know the difference between these two concepts. If there is any improvement in the BFT's limitations, let me know. Please answer. Thank you.
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68 views

Do Full Nodes validate all transactions and make new blocks after all bitcoin are mined?

Do Full Nodes validate all transactions after all bitcoin are mined? A fork of bitcoin core with all coins pre mined would be behaving in this way too I'd imagine..? Also, would these nodes still ...
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1answer
266 views

How does the 51 percent or 2/3 majority voting rule work?

For a block to be added to the chain, it needs vote from majority of miners, is that correct? If yes, does that mean a single block gets worked upon by all of the miners?
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Proof-of-Stake: What if a bad enactor is chosen by random?

My understanding of proof-of-stake is the following: The node that mines the next block is chosen, randomly in proportion to the amount of nodes they have in the network (ex. person who who owns 5% ...
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45 views

How do nodes come to consensus on whether a timestamp is valid?

From bitcoin wiki: A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. If a miner submits a block ...
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58 views

What are the biggest Proof-of-Stake roadblocks? [closed]

What are the biggest hurdles (technological or otherwise) that the Proof-of-Stake consensus algorithm must overcome to become the de facto consensus algorithm for blockchain? Or put differently, what'...
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1answer
28 views

What is meant with 'the highest PoW'?

What is meant when the nodes select the chain with the highest cumulated PoW? How is the highest highest PoW calculated? I thought the concept itself is called PoW.