A new vulnerability due to a previous patch update

Bitcoin ABC updated its client, the latest version 0.18.5, incorporating control points every ten blocks in the chain. As explained by the developers of this update, the intention is to prevent the realization of block reordering attacks, after the constant threats received by the Bitcoin Cash network (BCH) after the bifurcation of this November 15.

However, while the update reduces the risk of attackers rewriting the chain, it introduces a new attack vector that malicious miners can exploit, according to BitMEX. In the publication of the BitMEX research team, the crypto active change house ensures that the update allows an alternative attack to the reorg. As they explain, the addition of the checkpoint every ten blocks could enable a division of the “honest chain,” that is, the main chain.

The investigation states that as soon as block ten has taken place,  the attacker could mine a hidden parallel chain starting from that point.  In this way, some miners in the main Bitcoin Cash ABC network could undermine the malicious block first, while others would undermine the honest block.

Researchers at BitMEX believe that the control points can be “conflicting” for the Bitcoin Cash ABC network. In addition, they consider that the possibility of causing a division in the consensus “could be as damaging to the network” as the hostile reorganization of the blocks.

On the other hand, the Bitcoin developer, Eric Wall, states that checkpoints every 10 blocks also open the possibility that malicious miners also attack network nodes that “are still in the initial synchronization” or those that were temporarily disconnected.  Wall also stresses that only 10 blocks are required to take control of the network.

The attack, according to the developer, has a cost of 27,000 and does not require the processing power necessary to execute a 51% attack. In fact, the computer ensures that only one Antminer S9 is needed to manage to undermine the malicious chain. The possible alternative attacks are not the only problems facing version 0.18.5 of Bitcoin Cash ABC.

Another point of criticism of the new implementation is that it “gives developers more power and increases centralization.” The lecturer and promoter of Bitcoin Andreas Antonopoulos commented through his Twitter account that “you have to be skeptical about the change of power” in decentralized networks.

In this regard, BitMEX makes the caveat that the inclusion of these control points does not provide more power to the developers because, unlike the control points that the Bitcoin network had, in the new version of the Bitcoin ABC client “the points are automatically generated by the node’s software and not by the development team. ”

However, BitMEX states that at the moment it is not clear how the inclusion of these control points symbolizes a “substantial improvement” for the security of the BCH ABC network.
At the same time, the researchers believe that the new Bitcoin ABC client update did not have “the proper exploration” before launch. Above all, considering that the inclusion of checkpoints means a fundamental change in the consensus dynamics.

The After Threats, The Truce Arrives

The pre- and post-bifurcation tensions of Bitcoin Cash were numerous. The ecosystem was plunged into a  battle of hashrate and threats of mining pools. In spite of everything, the bifurcation took place, and this led to the launch of an update of Bitcoin Cash ABC.
Days after the launch of the update, Bitcoin SV promoter  Calvin Ayre proposed a truce between the altcoins.

Ayre said that he considers it is time to abandon the battle because Bitcoin SV is about the real Bitcoin Cash. In addition, the head of CoinGeek agreed not to bring legal action against those who attacked his pool during the bifurcation or against those who attacked his website a week ago. For its part, the developers and promoters of Bitcoin Cash ABC have not commented on this situation.