What is meant by a 51percent Attack.
A 51% attack refers to an attack on the blockchain (most commonly these attacks are still fictitious Bitcoin) by a group of miners who control more than 50% of the network's mining Hash-Rate or processing power.
By preventing new transactions from being
confirmed, an attacker can stop payments between some or all users. It also
allows you to reverse completed transactions while controlling the network,
allowing you to double use your coins.
You can almost certainly not create new coins
or change old blocks. The 51% attack will not directly destroy Bitcoin or any
other blockchain-based currency, even if it turns out to be extremely damaging.
look at a glance
--- Blockchain is
a distributed ledger that records all transactions performed on a
cryptocurrency network.
--- 51% attack is
a blockchain attack on a group of miners who control more than 50% of the
network mining hashrate.
--- An attacker
who controls most of the network can stop writing new blocks by preventing
other miners from completing them.
--- Changing past
blocks is difficult because we hard-code past transactions into Bitcoin
software.
How
a 51% Attack Works
Bitcoin and other cryptocurrencies are based on blockchain,
a form of distributed ledger. This digital file records all transactions that
take place on the cryptocurrency network and is available for review by all
users and the general public. As a result, no one can spend a penny twice.
(So-called “private blockchains” introduce authorizations that prevent certain
users from publicly viewing all data on the blockchain.)
As the name suggests, a blockchain is a
blockchain, which is a bundle of data that records all transactions completed
over a specified period of time. With Bitcoin, a new block is created
approximately every 10 minutes. Once a block is completed or disassembled, it
cannot be changed as a fraudulent version of the public ledger can be quickly
discovered and rejected by network users.
However,
by controlling most of the computing power on the network, an attacker or group
of attackers can disrupt the process of writing new blocks. It can prevent
other miners from completing blocks. In theory, you can monopolize the mining
of new blocks and get all the rewards.
Bitcoin
In the case of Bitcoin, the reward is
currently 12.5 newly created Bitcoins, but will eventually drop to zero. You
can block other users' transactions, send them, and then return them to make it
look like you have the coins you just used. This vulnerability, known as double
spending, is a fundamental cryptographic obstacle on which digitally perfect
counterfeiting and blockchains are built. Networks that allow double spending
quickly lose trust.
Changing the past block, which is a locked
transaction before the attack starts, would be very difficult even if a 51%
attack occurred. The further you are behind a transaction, the harder it is to
change the transaction. It is not possible to change a transaction before a
checkpoint. Behind the checkpoint, the transaction is hard-coded into Bitcoin
software.
On the other hand, the 51% attack form is
possible with less than 50% of the network's mining power, but the probability
of success is low.
51% Attack Real-World Examples
Two Ethereum-based blockchains, Krypton and Shift, were hit by a 51% attack in August 2016.
In May 2018, Bitcoin Gold, the 26th largest cryptocurrency
at the time, suffered a 51% attack. Malicious actors controlled much of the
hash power of Bitcoin Gold, so even if Bitcoin Gold repeatedly attempts to
increase the exchange threshold, the attackers will spend doubling over days
and eventually end up with $18 million in Bitcoin. You can steal more.
51%
Attack vs. 34% Attack
A distributed
ledger designed to achieve a fundamentally different but similar goal, the
Tangle could theoretically succumb to attackers providing more than a third of
the network hashrate known as a 34% attack.