## 2 Background and Related Work
### Hybrid Approaches Related to 51% Attacks  
The term 51% attacks refers to situations in which an attacker has 51% of the hashing power. As part of this attack, a private blockchain is created and completely disconnected from the actual chain edition. It is later introduced to the network as a real chain, which allows for a double-spending attack [47] Additionally, given that blockchain policy follows the most extended chain rule [56], if attackers gain 51% or more of the threat, they will push the longest chain by convincing network nodes to obey their chain. However, 51% of computational power is not strictly sufficient, so double spending is still possible if an attacker has less than half of the computational power [48]. The odds of success are low. A blockchain attack becomes increasingly expensive when the entire network acquires \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Consensus** & **51\%** & **Long-Range** & **DDoS** & **P + Epsilon** & **Sybil** & **Balance** & **BGP** \\
**Mechanism** & **Attack** & **Attack** & **Attack** & **Attack** & **Attack** & **Hijacking** \\ \hline PoW & Yes & No & Yes & Yes & Yes & Yes \\ PoS & Yes & Yes & Yes & No & Yes & No \\ DPoS & Yes & Yes & Yes & Yes & Yes & No \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Vulnerabilities of consensus mechanisms. increased hash power. A cryptocurrency with a high network hash rate may also be resilient to 51% attacks. To overcome 51% attacks, several studies and developments are being conducted. Researchers have proposed mixing proof mechanisms to eliminate 51% attacks. For PoW to be applied to a working network, the attacker must gain more than 50% of the processing capacity and more than 50% of the network wealth. This task is highly challenging for a user. In addition, the total cost should be considerably lower than the profit that an attacker might earn. The attacker's costs are much higher than the benefit in this form of a hybrid network. Additionally, this hybridisation implements other security measures to counter the attack [28]. Different studies and innovations have recommended different prevention methods, but they have several limitations in common. Komodo [57] introduced dPOW consensus, which takes a snapshot of the blockchain every 10 min and stores it in the blockchain. One of the more recent developments implemented by Horizon at Zen Coin is to delay the block in order to slow down the creation of blocks [29]. [PERSON] and [PERSON] provided a second hybrid PoS consensus using a BFT model with a two-thirds vote mechanism in the first 50 networks. This voting process is independent, resulting in unintended delays and an inconsistent block interval [30]. An alternative hybrid consensus algorithm was proposed by the authors in [31], namely, fork-free hybrid consensus with versatile proof-of-activity and the hybrid PoW-PoS-PoA algorithm. The authors introduced a technique where all PoW chains are created simultaneously and submitted to a committee for review. The committee determines and approves the most robust chain as the main chain. A weighted calculation amongst the committee members determines which chain is the best. On the basis of PoW power and PoS capacity, the weight of each committee member is calculated. This algorithm can also mitigate 51% attacks. However, other issues may affect the blockchain. One of the primary issues is determining how to distribute newly produced block rewards [27]. Another issue is that the interval between block generation is often inconclusive, which is directly related to the recently created currency [49]. Table 2 summarises various hybrid approaches and other solutions discussed in the literature. In conclusion, this study proposes a hybrid algorithm that combines PoS and PoW mechanisms to provide a fair mining reward to both the miner and validator.