Editor’s note: This article from the hash sent (ID:hashpie) Original: “Bitcoin Cash ABC” s Rolling 10 block checkpoints “, the author: BitMEX Rearsech, compiled: LucyCheng.
Beijing time on November 21st at half past eight in the morning, Bitcoin ABC official twitter posting said, Bitcoin ABC 0.18.5 version has been on the line. This version was added in the rolling block “checkpoint” as a deep restructuring of protection, to ensure that the transaction in the 10 time after the confirmation of the variable; in order to protect users, enterprises and exchange security.
Photo source: Bitcoin ABC official twitter
In this new system, as long as the block receives ten times can effectively determine the final confirmation. That is to say, even if the alternative chain has more work, as long as there is a conflict between it and check points, node will not switch to work more on the chain. From the current bitcoin cash two community alliance is the battle of the anxious state, adding new features of Bitcoin Cash ABC from Bitcoin Cash SV to defend and attack potential competitors. But BitMEX Research yesterday morning issued assessment report pointed out that the new system in the defense of the enemy attack depth at the same time, but also increased the risk of consensus chain splitting, and provides new opportunities for potential miners attack.
The picture from the BitMEX blog:
Security analysis of the new checkpoint mechanism
The analysis shows that the block size has been extended to 32 MB bitcoin cash, in a few cases more or less will delay phenomenon. If the delay is caused between nodes synchronization of less than ten blocks, a new checkpoint mechanism can still play a protective role. But if you reach 10 or more blocks are not synchronized, some users may choose to acknowledge the largest volume of effective chain chain; and conflict and check points are likely to lead to the consensus division, appear a new currency.
So, the checkpoint mechanism can not solve the delay problem brought by restructuring may reduce the risk of malicious; only depth restructuring, to reduce or limit in ten blocks. But from another point of view, this mechanism may also bring new opportunities for the miners hostile attack.
Provides a new method for miners hostile attack
Specifically, the attacker can secret mining length of 10 blocks or more “shadow chain”, “wait until 10 block honest chain” generated after segmentation when one-time release (that is to say, once the attacker received red block the release of shadow chain). This operation makes some nodes first to receive the red block, and part of the node is first received by the shadow chain and clashed with the checkpoint, which split the consensus chain.
Photo source: BitMEX Research
Of course, the shadow chain and honest chain deviate more than ten blocks, the former is not honest recombinant attackers may give up the chain, and stop these useless chain extension. But this attack to some extent will cause damage to the network, because it is cheaper than depth attacks, hostile miners can stop the attack earlier but more.
Although this assumption appears the probability is relatively low, but also need to have an attack force to achieve most; but they are with the new checkpoint system, trying to solve the problem of depth vicious reorganization, may occur. BitMEX Research so that, in a sense, the new checkpoint mechanism did not bring more substantial improvement for its defense against the attack.
The benefits of adding new mechanism
As mentioned above, this mechanism has opened up new ideas for hostile attacks, miners provide a new way to incite separatist consensus. But compared with can profit from the normal depth attack, reason and motivation to adopt this attack to destroy the network is not too obvious. And now, the attack is not clear, do not know what users will choose a chain and it is difficult to tell who will be the winner. And this kind of incentive is not obvious, may be positive for Bitcoin ABC, in a relatively long time in its security will be improved.
At the same time improve the safety part of the exchange and businesses of new mechanism can; because they can wait more than ten blocks of the assets included in the output within a user account. However, committed to improving the speed of transaction bitcoin cash, this may not be desirable.
Other questions from the community
In addition to security issues, for in the new version of the software to add check point this move and a common view is that, it provides more functions and powers for developers, thus increasing the extent of the center of the community. But in BitMEX’s view, the view is not applicable to this case; after all checkpoints are automatically generated by the node software, rather than manually inserted by the development team.
Picture: from twitter
On the other hand, Cinnober block chain and Eric Wall encryption currency at that checkpoint will likely bring new witch attack node. The so-called witch attack refers to destroy the reputation system through forged identity of peer to peer network. In the block chain system, not all nodes are running 24 hours, in the initial synchronization state or the node associated with the user may have temporarily closed a few days. The attacker only needs to start the relay nodes themselves, and will be broadcast at any time in the past generation chain length is ten blocks to the network node; let re on-line acceptance of the workload of lower chain and advance in the alternative chain checkpoint, so stay in another attack on the chain control. This seems to be a major defect checkpoint mechanism; at the same time contrary to the original set of Nakamoto – node can not affect the operation of the system under the condition of free to join or leave the network. So in some ways, Bitcoin Cash ABC gave up the idea of this upgrade.
In general, the Bitcoin ABC 0.18.5 version to make a fundamental change to the core network and solves the problem of dynamic consensus; at the same time, it also brings new crisis. Although the motivation and the cost benefit point of view, this change is unlikely to push the attacks, but risks still exist.