# Research on Progress of Blockchain Consensus Algorithm:
## 3 Blockchain Consensus Algorithm
### Byzantine Fault-Tolerant Consensus Algorithm
#### 3.3.3 PoS Algorithm  
Due to the obvious shortcomings of the PoW algorithm, such as waste of computing power and low efficiency in reaching consensus, the PoS algorithm was proposed in 2011.  
Figure 7: The working principle of the PoW algorithm.  
The PoS algorithm is the proof-of-stake algorithm. As soon as it was proposed, it was practically applied in the digital currency \"Peercoin\" in the following year, which is enough to show that the PoS algorithm has a certain application value.  
Different from the nodes of the PoW algorithm to obtain the accounting right through the competition of computing power, the PoS algorithm selects the node with the highest stake in the system as the accounting node. The PoS algorithm puts forward the concept of tokens. The stake of a node can be calculated based on the number and time of tokens held by it. The more tokens a node holds and the longer it holds, the higher its equity is. The higher the equity is, the lower the difficulty of \"mining\" is, and the higher the efficiency of finding the _target_ value of random number. After the node successfully obtains the accounting right of the block, its stake will be cleared, and the next round of stake accumulation will begin. The working principle of the PoS algorithm is shown in Figure 8.  
The advantage of the PoS algorithm is that it does not need to go through the complicated \"mining\" process and only needs to pass the proof of stake to obtain the accounting right; this in turn reduces the block time and transaction processing time and greatly saves the time for consensus reaching, and the consensus efficiency is significantly improved [69]. In addition, the PoS algorithm also saves and improves the consumption of computing resources compared with the PoW algorithm [70]. In the method based on the proof of stake, when a cyber-attack affects the stake of the entire system, it will also damage the stake of the attacker. The disadvantage of the PoS algorithm is that nodes with higher equity tend to obtain higher accounting rights, which reduces the enthusiasm of users with low equity to participate, thereby reducing the activeness of the entire blockchain.  
For subsequent improvements to the PoS algorithm, there is the Ouroboros algorithm based on security proofs, the Ouroboros Praos algorithm that adds identity confidentiality mechanism [71], and the Ouroboros Genesis algorithm that adds a self-starting process to prevent long-range attacks [72]. In addition, there is the Algorand consensus algorithm with high decentralization and low energy consumption [73]. This algorithm greatly reduces transaction time and is widely used in digital currencies. In 2014, the Tendermint algorithm proposed by [PERSON] [74] was optimized in transaction processing, with shorter transaction confirmation time and higher transaction throughput. In 2017, the Casper algorithm proposed by [PERSON] [75] combines the PoS algorithm with the PoW algorithm to ensure security and reduce energy consumption, but the transaction speed is not as good as the aforementioned algorithms such as Algorand and Ouroboros. In 2021, the LaKAS algorithm proposed by [PERSON] [76] is a new type of PoS algorithm, which greatly improves the transaction speed and reduces the risk of long-range attacks.