A software update pushed out by Bitcoin ABC after the Bitcoin Cash hard fork is reported to have included a vulnerability that puts the network at risk of a 51% attack.


Bitcoin ABC Update Problem

Since the hard fork of Bitcoin Cash that took place on 15th of this month, the bitter acrimony between the two factions has only gotten worse.

The resulting hash war has dragged the entire cryptocurrency market down. Amid all the social media bickering, both camps have encountered technical snags that expose the unpreparedness with which the changes are being made to the respective codebase of each version.

BSV (Bitcoin Satoshi Vision), the version backed by Craig Wright’s nChain, had encountered a bug that had split its network in two. Now, according to The Next Web, a vulnerability introduced to BCH ABC, Bitcoin ABC’s implementation, exposes the blockchain to the risk of a 51% attack.

The Vulnerability Explained

The Vulnerability Explained

According to the article, the Bitcoin ABC developers, anticipating a threat from rival blockchains, introduced a new line of code that is intended to change the way the nodes on the network decide whether a block is valid or not.

The earlier version of Bitcoin Cash used the proof-of-work algorithm to validate blocks on its network. With the update, the developers have introduced checkpoints that the miners will use to ensure they are working with the correct version of the blockchain.

The checkpoint is meant to protect the blockchain from attacks by using every 10th block for a dipstick check. A miner who encounters blocks that don’t match with the checkpointed version will automatically reject them.

However, cryptocurrency systems analyst Eric Wall believes that the change has introduced a new security risk.

According to Wall, a hacker that controls more than 50% of the hashrate will be able to submit 10 blocks together by reorganizing 9 valid blocks. An attempt by an attacker to submit the blocks at the same time as the network finding the 10th block can cause the blockchain to suffer a split.

Wall explained:

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.

He added:

The network will then have forked into two, and if there’s 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.

Community Reaction

The change, dubbed by many as arbitrary, has met with criticism from experts.

Andreas Antonopolous, a blockchain evangelist and educator, said:

It’s shifting consensus power to developers, away from miners. It is best to be skeptical about such shifts of power.

According to Wall, attackers with as little as $27,000 and using a standard cryptocurrency miner can control the ABC version of the blockchain.

It has become clear that the hash war that has dragged the entire market down is nothing but an attempt at one-upmanship. That the new chains serve no specific use-case and are not even well thought out is quite evident.

Do you agree with the analysis of Eric Wall? Let us know in the comments below.


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