## 2 Related Works
### The Vulnerabilities of Consensus Mechanisms  
A 51% Attack is the risk to the security of PoW by an individual or group taking over 50% of the blockchain's mining power [9]. This was further proven as a substantial risk to PoW blockchains when an attack on Ethereum Classic (ETC), which was a fork of Ethereum long before its move to PoS, actually occurred. After suffering from the probabilistic finality vulnerability, the value of the currency significantly dropped, causing the hash rate to also decline, leading to an attacker being able to carry out a 51% attack on the chain, partially due to the introduction of cloud mining services that let an attacker purchase mining power [6]. It suggests that a 51% attack is an important vulnerability in blockchain technology due to the damage it can cause and the likelihood of its occurrence.  
A Selfish Mining Attack allows the exploiter to increase their mining earnings while simultaneously negatively impacting the amount other nodes would earn [17]. Ref. [9] suggests the attack is conducted to obtain mining rewards that should not normally be obtained and take away rewards from honest miners. Research by the authors of [18] states that a miner equipped with only 33% mining power could earn in rewards what someone who had 50% of the mining power could earn through this attack; this information can be substantiated by the authors of [19], who also claim that 33% is a \"theoretical hard limit\" for mining power when it comes to the selfish mining attack. This is refuted in the more recent literature by [20], which conveys that only 25% of the mining power is needed for attackers to improve their rewards through this attack.  
A Double Spending Attack occurs when a bad actor exploits the time between two transactions [9]. This vulnerability to the PoW consensus mechanism is deemed to be impossible to avoid [9]. Ref. [12] proposes that there is no current way to prevent double-spending in the Bitcoin whitepaper, which further justifies that it is impossible to avoid but could be difficult for a malicious actor to attempt, with them possibly needing 50% of the total mining power to conduct the attack. However, the authors of Ref. [9] state otherwise, saying that double-spending attacks could occur with low mining power when combined with the selfish mining attack. Ref. [10] suggests that no instance of double-spending has been recorded. However, Ref. [21] indicates that there was a double-spending attack in March 2013, which resulted in a rapid drop-off in the price of Bitcoin. Ref. [22] clarifies and supports this, adding that the 2013 attack was due to a blockchain fork, which caused a conflict between Bitcoin versions, allowing two logs of Bitcoin to become available, enabling them to be double-spent.  
Refined Reorg Attack: Due to Ethereum's move to PoS being a recent change, fewer research papers have been released regarding any attacks on the new upgraded chain. However, Ref. [23] presents an attack called the Refined Reorg Attack on the new PoS Ethereum network, which could allow validators to earn more from validating blocks than others through the Maximal Extractable Value [24]. Ref. [23] details the attack as being that of a malicious actor who could propose a block in a slot, which keeps it hidden, while an honest block proposer would then place their block at the next slot, resulting in a bad actor being able to use both slots as a vote, which creates a probability that proposed blocks could be outnumbered by malicious actors.