What is a 51% attack and how to detect it?


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Regardless of being underpinned by blockchain technology that guarantees safety, immutability, and full transparency, many cryptocurrencies like Bitcoin SV (BSV), Litecoin (LTC) and Ethereum Traditional (ETC) have been topic to 51% assaults a number of instances previously. Whereas there are various mechanisms by which malicious entities can and have exploited blockchains, a 51% assault, or a majority assault as it is usually referred to as, happens when a bunch of miners or an entity controls greater than 50% of the blockchain’s hashing energy after which assumes management over it. 

Arguably the most costly and tedious methodology to compromise a blockchain, 51% of assaults have been largely profitable with smaller networks that require decrease hashing energy to beat nearly all of nodes.

Understanding a 51% assault 

Earlier than delving into the method concerned in a 51% assault, you will need to understand how blockchains record transactions, validate them and the completely different controls embedded of their structure to stop any alteration. Using cryptographic methods to attach subsequent blocks, which themselves are data of transactions which have taken place on the community, a blockchain adopts one of two types of consensus mechanisms to validate each transaction via its community of nodes and document them completely.

Whereas nodes in a proof-of-work (PoW) blockchain want to unravel complicated mathematical puzzles with a view to confirm transactions and add them to the blockchain, a proof-of-stake (PoS) blockchain requires nodes to stake a certain quantity of the native token to earn validator standing. Both method, a 51% assault may be orchestrated by controlling the community’s mining hash fee or by commanding greater than 50% of the staked tokens within the blockchain.

PoW vs PoS

To know how a 51% assault works, think about if greater than 50% of all of the nodes that carry out these validating capabilities conspire collectively to introduce a distinct model of the blockchain or execute a denial-of-service (DOS) assault. The latter is a kind of 51% assault through which the remaining nodes are prevented from performing their capabilities whereas the attacking nodes go about including new transactions to the blockchain or erasing previous ones. In both case, the attackers might doubtlessly reverse transactions and even double-spend the native crypto token, which is akin to creating counterfeit foreign money.

Diagrammatic representation of a 51% attack

Evidently, such a 51% assault can compromise the whole community and not directly trigger nice losses for buyers who maintain the native token. Regardless that creating an altered model of the unique blockchain requires a phenomenally great amount of computing energy or staked cryptocurrency within the case of huge blockchains like Bitcoin or Ethereum, it isn’t as far-fetched for smaller blockchains. 

Even a DOS assault is able to paralyzing the blockchain’s functioning and may negatively affect the underlying cryptocurrency’s value. Nonetheless, it’s inconceivable that older transactions past a sure cut-off may be reversed and thus places solely the latest or future transactions made on the community in danger.

Is a 51% assault on Bitcoin potential?

For a PoW blockchain, the likelihood of a 51% assault decreases because the hashing energy or the computational energy utilized per second for mining will increase. Within the case of the Bitcoin (BTC) community, perpetrators would wish to regulate greater than half of the Bitcoin hash rate that at the moment stands at ~290 exahashes/s hashing energy, requiring them to achieve entry to at the least a 1.3 million of essentially the most highly effective application-specific integrated circuit (ASIC) miners like Bitmain’s Antminer S19 Professional that retails for round $3,700 every. 

This may entail that attackers have to buy mining gear totaling round $10 billion simply to face an opportunity to execute a 51% assault on the Bitcoin community. Then there are different features like electrical energy prices and the truth that they’d not be entitled to any of the mining rewards relevant for sincere nodes. 

Nonetheless, for smaller blockchains like Bitcoin SV, the situation is kind of completely different, because the community’s hash fee stands at round 590PH/s, making the Bitcoin community nearly 500 instances extra highly effective than Bitcoin SV.

 Within the case of a PoS blockchain like Ethereum, although, malicious entities would wish to have greater than half of the full Ether (ETH) tokens which might be locked up in staking contracts on the community. This may require billions of {dollars} solely when it comes to buying the requisite computing energy to even have some semblance of launching a profitable 51% assault. 

Furthermore, within the situation that the assault fails, the entire staked tokens might be confiscated or locked, dealing a hefty monetary blow to the entities concerned within the purported assault.

Find out how to detect and stop a 51% assault on a blockchain?

The primary examine for any blockchain can be to make sure that no single entity, group of miners or perhaps a mining pool controls greater than 50% of the community’s mining hashrate or the full variety of staked tokens. 

This requires blockchains to maintain a continuing examine on the entities concerned within the mining or staking course of and take remedial motion in case of a breach. Sadly, the Bitcoin Gold (BTG) blockchain couldn’t anticipate or stop this from taking place in Could 2018, with a similar attack repeating in January 2020 that result in almost $70,000 price of BTG being double-spent by an unknown actor. 

In all these cases, the 51% assault was made potential by a single community attacker gaining management over greater than 50% of the hashing energy after which continuing to conduct deep reorganizations of the original blockchain that reversed accomplished transactions.

The repeated assaults on Bitcoin Gold do level out the significance of counting on ASIC miners as an alternative of cheaper GPU-based mining. Since Bitcoin Gold makes use of the Zhash algorithm that makes mining potential even on shopper graphics playing cards, attackers can afford to launch a 51% assault on its community while not having to take a position closely within the costlier ASIC miners. 

This 51% assault instance does spotlight the superior safety controls supplied by ASIC miners as they want a better quantum of funding to acquire them and are constructed particularly for a specific blockchain, making them ineffective for mining or attacking different blockchains.

Nonetheless, within the occasion that miners of cryptocurrencies like BTC shift to smaller altcoins, even a small variety of them might doubtlessly management greater than 50% of the altcoin’s smaller community hashrate. 

Furthermore, with service suppliers similar to NiceHash permitting individuals to hire hashing energy for speculative crypto mining, the prices of launching a 51% assault may be drastically decreased. This has drawn consideration to the necessity for real-time monitoring of chain reorganizations on blockchains to spotlight an ongoing 51% assault. 

MIT Media Lab’s Digital Foreign money Initiative (DCI) is one such initiative that has constructed a system to actively monitor quite a lot of PoW blockchains and their cryptocurrencies, reporting any suspicious transactions that will have double-spent the native token throughout a 51% assault.

Cryptocurrencies similar to Hanacoin (HANA), Vertcoin (VTC), Verge (XVG), Expanse (EXP), and Litecoin are just some examples of blockchain platforms that confronted a 51% assault as reported by the DCI initiative. 

Of them, the Litecoin assault in July 2019 is a traditional instance of a 51% assault on a proof-of-stake blockchain, despite the fact that the attackers didn’t mine any new blocks and double-spent LTC tokens that had been price lower than $5,000 on the time of the assault. 

This does highlight the lower risks of 51% assaults on PoS blockchains, deeming them much less engaging to community attackers, and is among the many causes for an rising variety of networks switching over to the PoS consensus mechanism.