It’s been a couple of days since Bitcoin Cash split into two separate blockchains and the results from the controversial hard fork are mostly negative (if you wanna know why hard forks suck click right here). One of them is the BSV (operated by nChain) and the other is BAB, the brainchild of ABC.
As of writing, both networks are struggling with severe technical difficulties. However, yesterday ABC’s vision of Bitcoin Cash rolled out an update that made things even worse. In short, if miners with bad intentions decide to launch a 51% attack they could easily do so.
Bitcoin ABC 0.18.5 has been released!
This release adds deep reorg protection to ensure that transactions are immutable after 10 confirmations. This safeguard helps users, businesses, and exchanges stay secure and free from disruption. https://t.co/wubd7LQYIz
— Bitcoin ABC (@Bitcoin_ABC) November 21, 2018
The update in question amends the way the mainnet verifies pending transactions. Originally, BAB relied on a classic Proof-of-Work algorithm but with recent changes “checkpoints” entered the game. Checkpoints make sure miners validate transactions on the original blockchain, and not on a copycat one. The idea is clearly to protect the network from “deep organization attacks”. Put simply, deep organization attacks happen when a group of highly-coordinated baddies tricks miners into mining a false blockchain. A successful deep organization attack could force the blockchain into nasties such as double spending and reverse transactions.
With the latest software update, every 10th block operates as a checkpoint. That being said, blocks which do not match the checked version of the ABC network will be automatically rejected by miners.
I don’t see why this is bad
Some security researchers voiced their concerns that this opens up space for 51% attacks. If someone takes over 51% of the network’s hashrate they could easily add ten artificial blocks by simply restructuring 9 checkpoint blocks. If this happens at exactly the same time when the network mines its 10th block (which it will assume as “honest”), this could result in a malicious and unplanned hard fork.
According to Eric Wall (as cited by Hard Fork) the arising issues are as follows:
“Since not all information gets propagated over the network at the exact same time, some nodes will see a 10-block reorganization, which they will reject, and others will see a [nine] block reorganization, which they’ll accept. […] The network will then have forked into two, and if there are two exchanges on different forks, it’s trivial for the attacker to sell the same cryptocurrency twice, on both these exchanges, and thus be double-spending.”
Other crypto geeks such as Bob MacElrath also voiced their concerns:
ABC officially abandons proof of work. Devs decide the correct chain. Also it's now easy to forcibly hard fork the network by causing a 10-deep reorg. Next up, Bitcoin ABCD! https://t.co/GiEv4ZzCrV
— Bob McElrath (@BobMcElrath) November 21, 2018
And to make things worse, it turns out that ordinary mining rigs and $27k are just enough to take the ABC network down.