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Questions tagged [attack]

Relates to attempts to harm the Bitcoin network. In cryptography, an attack is a method/technique to break the code. Bitcoin also has to deal with other types of attack, such as double spends and denial of service.

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Is there a limit to how many blocks can be rolled back from a 51% attack?

I was wondering if we where to ever face a 51% attack is there some sort of limit as to when the longest chain doesn't matter? For example if I owned 51%+ of the network, mined 1000 blocks privately ...
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1answer
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Possibility of broadcasting new block to only a fraction of honest nodes?

Consider in a block-withholding attack (aka selfish mining attack), attacker after creating a new block decides to broadcast this new block only to a fraction of network, such that eventually only a ...
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3answers
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What prevents DoS based on near-valid block timestamps?

Upon receiving a newly mined block, the block timestamp validation is performed here: https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L3263-L3270 Q1: As for the second check (block ...
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Mining Theory: A theoretical mining based attack

Okay, so, here is my scenario: Imagine a group of miners who are mining a coin are responsible for a large portion of the hash rate on the network (let's say not quite 50%). Looking at the parameters ...
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Why do we call it a 51% attack instead of a 50% attack?

From the Bitcoin paper: p = probability an honest node finds the next block q = probability the attacker finds the next block qz = probability the attacker will ever catch up from z blocks behind qz ...
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Hypothetical Scenario - Address collision with address with already confirmed outgoing transaction

In a typical case of finding a collision with an address, as long as the private key provided has a consistent public key that hashes to the address, then the coins in that address can be spent. The ...
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1answer
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Can corrupted unspent transaction outputs list leading to higher than expected fee be seen as an actual threat?

Let's imagine, an attacker managed to corrupt your local list of unspent transaction outputs (or a blockhain explorer you use) in a way that certain unspent transaction outputs seem to hold less coins ...
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How prevalent are coin attacks with botique altcoins?

I have deployed several altcoins using various PoW algorithms on my LAN for my buddies and I to mine/learn from. We ultimately want to go the distance of deploying an altcoin to the world, writing the ...
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How much computing power is required to bruteforce a Litecoin private key in reasonable time?

Say I want to break a Litecoin private key having the public key using brute force. How much computing power is required for that? Does any hardware exist which can find a matching private key in, say,...
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1answer
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What stops people attacking my new coin?

Say I just made a new altcoin. I mined it for a few days at some reasanoble difficulty - 2000 for example. I got to the 10 000th block and I am happy with my premine and network. Then, an attacker ...
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3answers
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Why can't mining pools provide fake transactions within the generated blocks?

Suppose Alice wants to add a fake transaction where she receives X ammount of BTC. I understand that in order to add that transaction to the blockchain she would have to compete against all the other ...
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1answer
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How does headers-first prevent fill-disk attack?

Checkpoints prevented an attack where a node could mine many many low-difficulty blocks from an early point in the blockchain and serve those blocks to syncing nodes who would see their disks fill up. ...
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1answer
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What is time warp attack and how does it work in general?

I am trying to understand the recent time warp attack on verge but since the attack is universal across all POW block chain i figure I could also ask here since people here are .. more knowledgeable. ...
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What exactly is selfish mining?

What is a selfish mining attack MonaCoin suffered from?
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1answer
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Why does Bitcoin no longer have checkpoints?

I've read that checkpoints in Bitcoin were removed because they were not preventing any meaningful attack. Why should a regular checkpoint not prevent majority attacks? For instance, if a checkpoint ...
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1answer
998 views

What prevents similar time-warp attacks in Bitcoin as happened to Verge?

Right now (may 2018), Verge (an altcoin with proof of work) was attacked by time-warp attack. More can be read here https://blog.theabacus.io/the-verge-hack-explained-7942f63a3017 What exactly ...
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Is the bitcoin blockchain really non-corruptible? [duplicate]

Some people say that proof of work is better than proof of stake, because it's not possible to rewrite the whole blockchain on-spot. One would need to "re-mine" everything. But I think this is not ...
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876 views

Miner modifies unconfirmed transactions and put it into the block

Is is possible that a miner modified a unconfirmed transaction (like changing the output of transaction to the miner himself) and put it into the local block, and after 10 mins the miner luckily ...
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1answer
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Is “fee higher than block reward” attack possible?

Imagine the following scenario: I send you 1000 BTC. After 6 confirmations, you give me what I bought. I create another transaction with 900 BTC to my own wallet and 100 BTC as transaction fee, using ...
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5answers
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Is this man-in-the-middle double-spending attack against Bitcoin viable?

There is an almost trivial double-spending attack against Bitcoin if an attacker has a MITM (man-in-the-middle) attack against a victim: the attacker prevents all blocks from being seen, and replaces ...
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2answers
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What happens if an ISP isolates a portion of nodes?

I came to believe that an ISP can easily detect full nodes, BTC connections and isolate them from reaching any other nodes. When and if an ISP decided to do so, could they easily perform a 51% attack ...
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1answer
281 views

resilience to sybil attack - public vs private

it appears that although not totally water-proof to Sybil attacks, Bitcoin network seems quite resilient to these kind of attack Preventing Sybil attacks. Is it true to assert that permissioned or ...
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If there is someone or a group with more than 50% of computation power and commits fraud, could we detect it and stop it? [duplicate]

I have been looking at the mining graph and noticed that if BTC.com, BTC.TOP and AntPool join together they could control the BlockChain. Graph: https://blockchain.info/pools
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POW based blockchains systems Majority Attack

TL;DR: With only 30% of network power a Majority Attack is possible and profitable. Am I missing anything? Generally speaking, blockchains based on Proof-of-Work authentications are using amount of ...
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2answers
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Cryptocurrency with addresses that cannot collide?

I had originally posted the following question here: Is it possible to have a cryptocurrency based on email address? And now I have come across The Large Bitcoin Collider I have read on Bitcoin ...
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1answer
186 views

What prevents rewriting the history of a chain with a different difficulty? [duplicate]

It looks like the difficulty is deterministic, but only if the timestamps are trusted. What's to prevent a large miner from starting back much earlier in the chain (when difficultly was miniscule) ...
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Flooding network with non-valid txs and blocks [duplicate]

Suppose I want to load the Bitcoin network. I can simply spawn lots of nodes and send many invalid txs and blocks in matter of seconds. I'm aware that honest nodes will not propagate what I send ...
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1answer
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What if some attacker forks blockchain from height 1 with a constant difficulty 1?

I've been reading Satoshi's paper recently. There's one thing I cannot think through. That is because the target will limit the block production speed to 2016 blocks per two weeks on average no ...
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1answer
249 views

How does the Bitcoin network deal with bad actors?

Can someone explain at a high level how the network deals with bad actors (either intentionally (ie- attacker) or unintentional (ie- misconfigured node or a node running outdated code, forked code, ...
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1answer
109 views

How much money would it take to bribe the majority of miners to attack the system?

I think this question is just a re-formulation of the 51% attack, but it has me thinking: miners are monetarily incentivized to not perform a 51% attack, but there must be some amount of money will ...
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1answer
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Can a bad actor omit an unspent address from a pruned chain?

This isn't a problem today, because if I want to run a pruned node then I still have to download the whole chain, but it sure would be nice if I could just download a pruned chain instead and validate ...
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1answer
102 views

Can a Bitcoin ( or any other cryptocurrency ) be compromised with a large botnet/s?

I'm new to cryptocurrencies, so I recently read the paper from the Satoshi Nakamoto ( link is here ) to know a little bit more about the Bitcoin.And I saw this statement: What is needed is an ...
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1answer
208 views

51% attack clarification

Im just reading a book on the basics of blockchain and I encountered a confusion regarding the 51% attack. If I'm right, it says that an attacker holding 51% or more of the network's computing power ...
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1answer
210 views

Attack vectors for difficulty retargeting with BCH and BTC?

Since the existence of BCH, miners can now switch chains to mine on. Assuming they mine greedily based on price and difficulty. Can the following attack happen and how could it be mitigated: Assuming ...
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2answers
325 views

How does changing transaction data in a block change the hash of previous block?

I am reading this article, within which it mentions that "Imagine this for a second, a hacker attacks block 3 and tries to change the data. Because of the properties of hash functions, a slight ...
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1answer
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What prevents a node from sending a different version of the blockchain?

I understand that proof of work prevents a node from creating a new version of the blockchain unless they have >50% of the hash rate, but what if the attacker is also able to intercept the victim's ...
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3answers
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How exactly bitcoin consensus rules are forced?

There are some rules, called consensus rules. For example, block generation fee amount. And it is said that "change to consensus rules is hard-fork". But how exactly the consensus rules are forced? ...
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Protect against Ddos when there were few nodes

I can imagine that Ddos is nearly impossible today because of the distributed nature of the Bitcoin architecture. How did the Bitcoin distributed architecture protect itself against a Ddos in the ...
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2answers
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What happens if 1-way functions no longer exist?

Advances in AI and nanobiotech can radically increase intelligence to the point where unsolved mathematical problems get solved. What happens to Bitcoin (and other cryptocurrencies) if ⨕&...
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4answers
124 views

What can an attacker who controls majority or all of the full nodes do?

What happens when a strong attacker has control of majority or all of the full nodes? What damage can he do and would they be reversible?
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1answer
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Can one node receive two transactions from the same user (doublespend)?

I'm learning how the blockchain works. I've read that when someone (say Alice) send twice a transaction to two different peoples (Bob and Charlie) such that Alice has only enough to pay Bob or Charlie,...
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What stops this style of attack on the Bitcoin network?

I was having a look at the genesis block of Bitcoin earlier and noticed the difficulty was set to 1. I guess this was originally designed so just Satoshi's computer mining at this difficulty would ...
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3answers
7k views

Attacking Bitcoin with a supercomputer

The difficulty in Bitcoin is recalculated every 14 days. What if immediately after this difficulty adjustment someone targets Bitcoin nodes with a supercomputer and start creating new blocks? Such ...
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0answers
322 views

Can a private key enumeration attack be used to steal bitcoins? [duplicate]

Let's consider the following algorithm enumerate all of the private keys for each of the enumerated private keys, generate the relative public key and verify whether there is any unspent coin ...
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Estimation of cost of the adversary implementing a prevent delivery of block attack

I am trying to understand which is the cost of an adversary(A) when he tries to prevent the delivery of a block in the entire network. I know that in order the A to succeed he has to be an immediate ...
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1answer
114 views

How does intial block download work at P2P layer?

A simple DOS attack while IBD could be as follows: The fresh client is currently downloading block 100. Then it is offered 10 blocks at height 101, each claiming they are the heaviest chain 9 out of ...
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254 views

How to perform DoS attack on Bitcoin peer?

Firstly I am aware of this questions: Is bitcoin vulnerable to a DOS/spam attack? and What protection does Bitcoin have against Denial of Service (DoS) attacks?. I am aware of the transaction fees and ...
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1answer
150 views

Force a fork - is that possible?

I am having a question regarding forks. We had a discussion about attacks on bitcoin in class recently. One of the attacks was about how an attacker gains some advantage if he is able to mine a block ...
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1answer
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How can't a malicious attacker generate bitcoins on his private network?

I'm new to the cryptocurrencies world and I'm trying to understand how all this stuff works, so expect a really noob question. Suppose there's a user which generates a number of addresses and sets ...