Bitcoin Cash vulnerable to 51% attack after recent miner exodus

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Updated on Apr 28, 2020

Reading time 3 minutes

BCH miners recently massively left the BCH network, causing its hash rate to drop by over 80%.
The move happened after a recent block reward halving, which reduced rewards to 6.25 BCH per block.
While the miners have migrated to the BTC network, many wonder whether the same fate will befall BTC itself.

Bitcoin Cash (BCH) recently went through its block reward halving, only a little over a month before Bitcoin’s own halving is supposed to take place. However, BCH halving did not go well, and it had very negative consequences on its hash rate.

After the halving, numerous miners decided to leave, causing the hash power to drop by over 80%. The drop happened within only two days, which is a very harsh and very sudden change for the major crypto.

https://twitter.com/MyLegacyKit/status/1248155683876470786

However, the new development also puts BCH in danger, as it is now vulnerable to 51% attacks. Some estimates say that bad actors could rent enough hash power to take over BCH with only $10k per hour.

BCH hash rate drops dramatically as miners shift to BTC network

The miners’ departure from the BCH mining sector comes as a consequence of a block reward drop. The rewards have gone down from 12.5 BCH to 6.25 BCH per block. This is the same development that Bitcoin itself will see in about a month. However, despite that, many of the BCH miners seem to have migrated to the Bitcoin network.

New data from f2pool reveals that the Bitcoin Cash hash rate dropped from 4,200 PH/s to only 720 PH/s. As mentioned, the drop happened in only two days after the halving, Fortunately, it quickly started to grow again over the last several hours, surging back to 1,600 PH/s.

Meanwhile, Bitcoin itself saw around a 30% increase in hashrate at the same time. This clearly indicates that miners have migrated from BCH to the BTC network.

BCH blockchain was taken over once before

Meanwhile, BCH remained highly vulnerable to 51% attacks. Crypto51 estimates that less than $10k per hour could allow someone to take over the network. The exact amount needed to hijack BCH blockchain was $9,130 per hour, using rented hash power.

Something like that already happened on May 24th last year. Back then, the ‘attackers’ were two of the largest BCH mining pools, BTC.top and BTC.com. They took over the network in a white-hat 51% attack to prevent bad actors from doing the same.

Now, many speculate whether this development is a preview into what will happen to BTC itself once the halving takes place. This is more than likely, as BTC miners tend to leave even faster than BCH miners. If it happens, Bitcoin is likely to be in a lot of trouble in about one month.