How to break the blockchain and cryptocurrencies: 6 successful attacks "51 percent"

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    One of the main threats to information security for cryptocurrencies created on the blockchain technology is the so-called 51% attack. They allow attackers to control the network and the transactions taking place in it. In 2018 the victims of such attacks have become six kriptovalyutnyh projects.

    What is "attack 51%"

    Cryptocurrencies are based on blockchain networks, that is, distributed registries that store information about all transactions that have ever been made in blocks. The work of these registries is supported by miners - they are engaged in confirming transactions, generating new blocks and adding them to the blockchain. For this job, they are entitled to remuneration in cryptocurrency.

    In networks based on the PoW (Proof-of-Work) consensus algorithm, in order to add a new block, miners need to perform complex calculations in order to prove that they have done work. The one who manages to solve the problem first gets a reward. The more miner computing power, the higher the probability to solve the problem first.

    This importance of computing power makes it possible to attack 51%. Its essence lies in the fact that several miners with significant computing power (hashrate) can receive a “controlling stake” in the network, that is, they have the most hashrate. As a result, they can create blocks at their own discretion, manipulate bilateral operations, and not confirm transactions - this makes it impossible to spend the same money multiple times (double spending).

    This year, the victims of such an attack were six well-known cryptocurrency projects.


    The project came under attack in April 2018. This altcoin was launched based on the CryptoNight algorithm. After the attack, the developers managed to increase the security level of the project.


    The cryptocurrency popular in Japan was attacked in May of this year. At the time of the attack, the project used the Lyra2Rev2 algorithm. The attackers managed to hack it, the damage from their actions was estimated at $ 90,000.

    Bitcoin gold

    The Bitcoin Gold coin was attacked twice - for the first time on May 16 and then three days later. As a result, the damage from exceeded $ 18 million, and cryptocurrency exchanges began to exclude Bitcoin Gold from listing.


    The crackers managed to use the Lyra2Re algorithm to attack the cryptocurrency network Verge. As a result, about $ 1.4 million was stolen .

    Litecoin Cash

    In late May, the Litecoin Cash coin network was under attack . At the same time, developers managed to cope with it fairly quickly, which prevented large-scale losses.


    In early June, another attack of 51 percent occurred - this time the ZenCash network was the victim. The attacker managed to seize control of the network for several hours. As a result, he managed to spend two cryptocurrencies on $ 30,000.

    How to protect

    The technology of distributed registries, a vivid example of which is the blockchain, is gradually being implemented in various sectors of the economy, including in government bodies. The growth of interest in the blockchain is also influenced by the myth of its security. It is believed that since it is built on the basis of complex cryptoalgorithms, then no additional security measures are required.

    Attacks like those described above show that security problems exist in the case of the blockchain. This means that everyone who decides to use this technology will need to think about ensuring information security.

    On Thursday, October 11, at 2:00 pm, Ivan Melekhin, Deputy Director for Business Development in Russia, during a free webinar, will talk about the security of the blockchain. At the webinar, the blockchain device, its components and their inherent risks and threats will be reviewed in detail. Ivan will also give examples of real incidents and vulnerabilities discovered during the security analysis conducted by the Positive Technologies research center.

    The webinar will be of interest to heads of IT and IS departments, who are considering the possibility of using the blockchain in their organization, project managers and professionals responsible for implementing the blockchain.

    To participate in the webinar you need to register .

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