Since ZenCash's mining algorithm is Equihash, other chains such as Bitcoin Gold, Bitcoin Private or Zclassic are also vulnerable. Zcash, which uses the same algorithm, has a greater processing power, so the attack could involve the deviation of mining power from its chain to ZenCash, although this possibility has not yet been confirmed.
According to Crypto51, a portal that calculates the cost of such attacks, a 51% attack time against ZenCash would cost just over $ 7,000. The cryptoactive network, ZEN, has a current value of 26.83 dollars, which represents a retraction of 7.87%. It has a market capitalization of $ 106,992,130 and a running total of 3,988,300 ZEN.
According to the team, any network using such an algorithm is vulnerable to a similar attack which urged that exchange bureaus raise the number of confirmations required for their transactions to 100, in order to "mitigate" the possibility that a 51% attack or block withholding may carry out double-spending transactions.
51%, block retention and double spending
A 51% attack implies that the aggressor concentrates more than half the processing power of a given blockchain and can handle at will the registration of the network. In this way, you can reverse blocks and cancel transactions already made to exchange houses.
In a block retention attack the amount of power required is lower (theoretically works with 30%, depending on the size of the block). network). The attacker must mine an alternating chain with the transactions that he wishes to introduce in the network, make a transaction, reverse it with the mining power he has in his hands and introduce his chain of alternate blocks in the original chain. Since it has a larger number of blocks, it is considered valid by the rest of the nodes.
In both situations, it is possible to perform double-spending transactions as in this case. These operations, usually carried out against exchange houses, involve very large deposit or withdrawal orders that are eliminated before they are registered in the network, causing the exchange to liquidate the operation but remain without the support of the coins.
This type of operator generally expects few confirmations to accelerate the exchange process of its users, making them prey to an attack that can modify the state of the network before the registry is inviolable.
In recent weeks several similar events have occurred, suffered by cryptocurrencies such as Verge and Bitcoin Gold, where the welfare of the network was compromised. The case of Verge is paradigmatic since he has already received  4545007] three attacks in less than 3 months even though he applied hardfork after the first event.
Attacks of this nature can seriously compromise the current blockchain scenario, since their erosive forces jeopardize the proper functioning of the networks, for the benefit of those who can finance attacks of this nature.
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