# A Compute and Wait in PoW (CW-PoW) Consensus Algorithm for Preserving Energy Consumption
## 3 Consensus Protocol Overview
In the execution phase of the proof, \(V\) simply asks \(P\) to open the labels corresponding to certain nodes chosen at random. Proof of Space-Time (PoST) is another consensus algorithm closely related to PoC. PoST [22] differs from proof of capacity in that PoST allows network participants to prove that they have spent a \"space-time\" resource, meaning that they have allocated storage capacity to the network over a period of time. The authors called this 'Rational' Proofs of Space-Time because the true cost of storage is proportional to the product of storage capacity and the time that it used. The rational proof of financial interest in the network achieved by PoST addresses two problems with proof of capacity. The first, Arbitrary amortized cost: In a consensus system that doesn't account for time, participants can generate an arbitrary amount of PoC proofs by reusing the same storage space, and lowering their true cost. The second, Misaligned incentives: A rational participant in a PoC system will discard almost all stored data whenever computation costs less than the data storage do. This essentially turns PoC into a partial PoW system, which is potentially more resource-intensive. An extension of Bitcoin's PoW via PoS is presented in Proof of Activity (PoA) by [PERSON] et al. [23]. Miners start with PoW and claim their reward. The difference is that the extracted blocks do not contain transactions. They are simply templates with header information and the mining reward address. Once this nearly blank block is mined, the system switches to PoS. The header information is used to select a random group of validators to sign the block. They are coin holders (stakeholders) and the greater the stake held by a validator, the more likely he or she will be selected to sign the new block. Once all the chosen validators have signed the block, it becomes an actual part of the blockchain. If the block remains unsigned by some of the chosen validators for a given time, it is rejected as incomplete and the next winning block is used. Validators are chosen again and this continues until a winning block is signed by all selected validators. The network costs are divided between the winning miner and the validators who signed the block. PoA is criticized that too much power is still needed to mine blocks during the PoW phase on one hand. On the other hand, coin accumulators are even more likely to make the signatory list and rack up more virtual currency rewards. A random mining group selection to prevent 51% Attacks on Bitcoin is proposed in [24]. The authors divide miners into several groups. Each peer node determines its mining group using the Hg (\(\cdot\)) hash function and its wallet address. Additionally, once a block is created, its hash value is used with Hg (\(\cdot\)) to determine which mining group is supposed to find the next block. Only even nodes belonging to the mining group are allowed to mine the next block and to compete with each other. Once a block is propagated over the P2P network, other nodes can check if the block was generated by the correct mining group by comparing the hash value of the previous block in the header of the block with the address of block creators. Here, although there may be an attacker with more than half of the total hash power, the chances of a successful double-spend attack can be greatly reduced by increasing the number of mining groups as the mining groups are chosen at random. In addition, the computational power required for block mining is effectively reduced by 1/(number of groups) because even nodes not belonging to the selected group do not participate in PoW and the difficulty level can be lowered due to the smaller number of competing miners in each group. The authors show that if the number of groups is greater than or equal to two, the probability of the attacker of finding the next block is less than 50%.