Attack on BSV: 51% Explained
Recently, Bitcoin SV (Satoshi Vision) has suffered yet another %51 attack on it's blockchain, which has caused the birth of multiple malicious sidechains, orphaned the genuine chain and it's trustworthy nodes and, most importantly, tanked the price right through its most critical support and is now on the brink of being delisted from major exchanges.
Not that this is to anyone's surprise, really. Bitcoin SV has garnered itself something of a bad reputation in the cryptocurrency industry, especially when the one spearheading it is a moron claiming to be Satoshi. It was only up to Murphy's law at this point to take effect, and it has cemented itself as the worst Bitcoin hard fork to exist right now: Completely untrustworthy, without merits and with huge red flags roundabout. And the 51% attack only proved the obsolescence of this fork even further, as well as the narrative around BSV will remain unchanged for a very long time.
In reality, Murphy's Law always comes to fruition, especially when it comes to PoW technology, which is seriously beginning to age as it's computationally expensive to operate. We might witness this even with Bitcoin in the very distant future. As it stands now, there is always the chance for mining difficulty to become unbalanced at some point, resulting in a few powerful mining entities controlling the consensus process and any consensus change or protocol change. I do think we'll see a SHA256 replacement at some point, but it could be as soon as 2030.
The %51 Attack
There are a number of different definitions of a 51% attack floating around on the internet. The most common definition is that a 51% attacker creates an alternate copy of the blockchain, and propagates that to users. The blockchain that the “official” Bitcoin blockchain uses has a different set of block producers than the alternative chain, and the miners on the two blockchains would have to choose between which chain to use when they started mining. The criteria by which previously offline nodes choose which chain to mine in is described in the Bitcoin white paper: The longest sustained chain is favoured over the shorter one, and as more nodes come online, the attacker will now have a majority of the total computing power in the network. This will make any attack on this network unstoppable.
This type of attack is usually described as a pre-defined alternate chain (abbreviated PACT). In other words, it’s a blockchain that a network can use to “replace” the original chain.
A second definition is one of more commonly used, of a 51% attacker doing nothing more than mining on a block on the original blockchain, and broadcasting it to users (sometimes in an attempt to confuse users about which chain is genuine).
A third, more technical definition is that a 51% attacker is using any means to get more than 50% of the blocks on the network to be invalid. This is the more correct definition. Note that even the more technical definition is only correct if that attacker is mining on the “original” blockchain.
A final popular definition is that a 51% attacker is any miner who has more than 50% of the total computing power on the network. While that is technically correct, it’s also incomplete, as that 50% rule only applies to the “original” blockchain.
When we say a coin “has a 51% attacker”, we’re not just talking about a single entity. There will be lots of different actors who are contributing in some way to the block generation, and each of these can be part of a 51% attack. In fact, the original definition of 51% is based on the assumption that every single miner is a possible attack, and the definition of a single entity being able to do that is simply not true.
The best definition is the last one above. There is no way for a single entity to have more than 50% of the total computing power in a blockchain. The only way you can get more than 50% of a blockchain is by pooling together all the mining from multiple entities. It’s simply not possible for a single entity to have more than 50% of the total computing power.
What can an attacker do?
The simple answer to that question is: they can make the Bitcoin SV network go to hell in a handbasket, provided the attack has enough time to sustain itself. There’s also more nuanced, complex explanations but I'll keep it simple:
Basically, if an attacker takes control of a large portion of the network, they can make blocks, but they cannot produce blocks at the same rate as the network can produce blocks on the main chain. They cannot produce blocks on any other chains because blocks get confirmed to the main chain first.
Thus, a chain reorganization may occur when there are more blocks in the orphan chain than in the main chain, allowing some blocks in the orphan chain to be considered valid blocks in the main chain.
For example, in an attack, the attackers are able to “reorg” the chain. This results in the creation of a longer orphan chain, resulting in a chain reorganization and an attack on the coin. Once the coin has no connection to the main chain, it is vulnerable to double spends.
But what is a double spend?
This is the most common attack vector against any PoW-based Blockchain out there, some even synonymize it with the 51% attack.
Let’s imagine the following situation: Alice pays Bob £10 in Bitcoin. They have a two-of-three multisignature address, which requires Alice, Bob and Carol to sign a transaction to send the funds. Alice signs her address using only one of Bob’s addresses, and sends the transaction to Bob’s multisig address. Bob signs his address using only one of Alice’s addresses, and sends the transaction to Alice’s multisig address. And finally, Carol signs the transaction using the other address.
In this case, Carol has the power to spend Alice’s funds twice. If she spends £10 from Alice’s address, she receives £10 back from Bob’s address, and £10 from Alice’s address. However, if she spends the same £10 from Bob’s address, she receives £10 from Alice’s address, and £20 from Alice’s address, because Alice is no longer able to spend her own funds from the second transaction.
Double-spending may seem like a complex concept, but it’s an important one for understanding the concept of an orphan chain.
Conclusion
Ultimately, PoW technology is beginning to age, and will likely phase out of the picture with the last standing being Bitcoin, perhaps Litecoin as well. The computational expense cannot be overestimated compared to other methods to achieving decentralized consensus.
In regards to BSV, I cannot help but see it as an illegitimate, spineless fork of Bitcoin with nothing but a catchy name attached at the end of it. It exist as if it knows something Satoshi didn't at the time BTC was created, and as if somehow, along the line, we strayed from the original vision he envisaged for BTC. I couldn't care less for BSV anymore, and it's supporters still to this day confound me.
Blockchain illustration made by me
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