## 2 Background and Related Work
### Consensus Mechanisms
#### 2.4.3 DPoS  
DPoS is a consensus process that allows shareholders to vote on the nomination of witnesses [52]. In DPoS, the main objective is to minimise energy waste and accelerate transaction times. As a result of the overall block generation process, this consensus mechanism operates much more quickly than PoW consensus. In DPoS, each stakeholder is allowed to cast one vote per share; they can cast additional votes when they own additional coins. Moreover, the witnesses are rewarded for producing blocks and penalised for failing to do so, such that they are not paid and are voted out of office. To complete the instructed task, witnesses should receive the largest number of votes from random stakeholders. A stakeholder also votes on the restructuring of the delegates and adjusts the network, which will be reviewed by the stakeholder before a final decision. Although DPoS was designed to increase transaction efficiency and overcome the constraints imposed by many other consensus mechanisms, it has significant shortcomings. The network is not sufficiently decentralised due to a large number of validators. A centralised system may serve as a focal point for random intruders due to its centralised nature. DPoS is susceptible to 51% attacks because an attacker will convince stakeholders to give them 51% voting power in a 51% attack [40]. Asymmetric agreements are also vulnerable to other types of attacks, such as long-distance, DDoS, P + epsilon, Sybil and balanced attacks.  
This work investigated the fact that the three main consensus systems, which are susceptible to several attacks, have significant weaknesses. As a result of their vulnerability, digital transactions are at a high risk of being attacked. Table 1 summarises the results of our analysis. The 51% attack can exploit all three consensus mechanisms, making it desirable for attackers, particularly for PoW where achieving the required hashing power is cost-effective.  
The following is a brief description of several severe attacks. However, the focus of this study is on 51% attacks. Long-range attacks are the result of a weak model of subjectivity [53]. This form of attack is similar to the 51% attack. It appears to fork the chain from the genesis block [54] rather than confirming the sixth block. This type of attack occurs very rarely in Bitcoin, but it can be damaging when demonstrating stakeholder consensus (PoS) and delegate stakeholder consensus (DPoS). Assuming a PoS consensus scenario in which the invaders begin with a limited number of coins shortly after the genesis block, their chain versions can be privately mined to carry out the attack. Given that they have a small stake, they will generate a limited number of blocks at the beginning and then generate a longer chain. PoS does not specify a threshold for chain lengthening, so the chains can become extremely long. The P + Epsilon attack is a method of exploiting the dominant strategies of the participants in the network. PoW-based blockchains are usually vulnerable to this type of attack [55]. When attackers give participants a pay-out in order to gain an advantage, a payoff matrix is used where the dominant tactic facilitates the achievement of the attacker's objectives. As a result of the attack, the participants do not receive any compensation, and the attacker receives the entire amount. This key statistical finding is based on an ad hoc selection model.