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51% Attack

51% Attack

A 51% attack (or majority attack) alludes to a possible attack on the integrity of a blockchain system in which a single malicious entertainer or organization figures out how to control the greater part of the total hashing power of the network, possibly causing network disruption.
On the off chance that a single terrible client, or group of terrible users acting together, control over half of the total network hashing rate for a blockchain, they are able to override the consensus mechanism of the network and commit malicious acts like double spending. The attacker would have sufficient mining power to intentionally alter the ordering of transactions, keeping some or all transactions from being confirmed (otherwise known as. transaction denial of service). He would likewise have the option to keep some or any remaining excavators from mining, leading to the supposed mining monopoly.
For instance, on the off chance that a malicious entertainer was to take more than 51% of the hashing power of the Bitcoin network, they could make an offline OTC trade by sending some Bitcoins to a cryptocurrency wallet in exchange for USD. Taking into account the implied immutability of the blockchain, when the transaction is confirmed by the network hubs, the buyer would gullibly hand over the USD to the trickster.
The malicious entertainer could then return in the blockchain to the block before the BTC transfer was confirmed and mine an alternate chain, in which the BTC transfer is excluded. The majority share of the networking power would guarantee that this is forced to be adopted by the remainder of the network as a substantial transaction.
Then again, a majority attack doesn't permit the malicious entertainer to keep transactions from being communicated nor to reverse transactions from different users. Changing the block's reward, making coins out of nowhere or taking coins that never had a place with the attacker are likewise entirely improbable situations.
The further back a transaction is, the harder it is undermine it, as the number of new blocks to be mined to bring the network up to the current level turns out to be endlessly further away. This is the motivation behind why Bitcoin transactions typically require a threshold of x number of affirmations before clearing.
A 51% attack on the Bitcoin blockchain is impossible in view of the size of the network. As the network develops, the possibility of a single person or entity getting sufficient computing power to overpower the wide range of various participants gets increasingly improbable.
In this way, 51% attacks are exceptionally far-fetched to occur on big networks, particularly on the Bitcoin blockchain, which is viewed as the most solid cryptocurrency network. While a considerable lot of the large blockchains have not yet experienced an attack of this sort, the majority attacks have been seen on other more modest chains. For example, the altcoin Bitcoin Gold - which is a fork from the primary Bitcoin chain - experienced a 51% attack in May 2018, leading to the theft of $18 million worth of BTG at that point.


  • Albeit a fruitful attack on Bitcoin or Ethereum is improbable, more modest networks are continuous targets for 51% attacks.
  • Blockchains are distributed ledgers that record each transaction made on a cryptocurrency's network.
  • A 51% attack is an attack on a blockchain by a group of excavators who control over half of the network's mining hash rate.
  • Attackers with majority control of the network can intrude on the recording of new blocks by keeping different excavators from finishing blocks.
  • Changing historical blocks is troublesome due to the hard-coding of past transactions into Bitcoin software.


Will Ethereum Be 51% Attacked?

A fruitful 51% attack against Ethereum is improbable, for similar reasons given above for Bitcoin. Despite the fact that Ethereum is a more modest network, making an obvious objective for a 51% attack is still too large. Besides, this risk is probably going to vanish as Ethereum changes to a proof-of-stake network.

How Likely Is a 51% Attack Against Bitcoin?

An effective 51% attack is viewed as incredibly improbable, due to the restrictive cost of collecting sufficient hash power and power to commandeer the network. As of April 2022, the Bitcoin hash rate is almost 220 Exahashes each second, implying that it would take around 10,000 of the most advanced mining apparatuses to send off a fruitful attack. Any party capable of such an attack would probably have more to gain by legit mining and gathering block rewards.

How Could Networks Prevent a 51% Attack?

There are several methods for moderating the risk of a 51% attack, albeit the risk can't be totally wiped out by proof-of-work networks. A fruitful 51% attack turns out to be fundamentally more costly for digital currencies that utilization ASIC excavators, given that no larger cryptocurrency is mined by a similar algorithm. Bitcoin Cash presented a system of ten-block designated spots, making transactions irreversible after a certain period of time. Other digital currencies have endeavored to secure their networks utilizing ASIC excavators, ChainLocks, or changes to the consensus algorithm.