PoDC (Proof of Double Committee) consensus algorithm
In essence, the key problem with blockchain distributed ledgers is the random selection of block creators. This randomness can be seen across the entire network and must be absolutely impossible to manipulate and predictable. If not, a malicious node can manipulate the random number to control the main chain for a long time. Therefore, double-payment attacks can also be achieved.
ReapChain’s algorithm is a method to improve the problem of this consensus, and the block generation is agreed through a random method through double committee and quantum random number.
1. PoDC consensus algorithm and double committee
1) double committee consensus algorithm (Proof of Double Committee)
ReapChain has implemented a new consensus algorithm, double committee consensus algorithm (Proof of Double Committee), which improves the existing DPoS and PDFT methods.
ReapChain operates standing committee nodes and steering committee nodes to balance between the internal and external nodes and forms a double committee to conduct the consensus process.
In ReapChain, only 29 nodes (the standing committee: 14 nodes, the steering committee: 15 nodes), participate in the consensus process even if the number of nodes on ReapChain increases. The participation ratio of the steering committee nodes in the consensus process is maintained over 51% all the time to insure decentralization. Since standing committee nodes which operate all the time are also replaceable through a vote, management of total nodes operation is transparent.
2) double committee
PoDC aims for decentralization in constructing the standing and steering committees.
The standing committee nodes initially operates in the governance community. It can be further selected by those candidates that meet the particular criteria of standing committee amongst the steering committee nodes. And if any of the existing standing committee nodes are suspended or fail to meet the criteria, then those nodes must go through a separate voting process of the governance to be promoted from steering to standing committee node status.
Standing committee nodes: 14 Nodes that operate all the times in ReapChain and have authority to create a block by participating in consensus process. (condition for the standing committee node: 2% stakes of the total issuance [98 million REAP] staking)
Steering committee nodes: 15 randomly selected nodes among steering committee candidate nodes by using quantum random number, and can participate in consensus process to verify transaction(condition for the steering committee node: Stake of 100,000 REAP).
ReapChain consists of 14 standing committee nodes that operated at all times as well as 15 steering committee nodes that had selected from general nodes through unpredictable quantum random numbers comprises of robust security. These 29 committees participate in the consensus process for generating blocks. In order to ensure whether the standing committee that operated at all times is still working legally, the steering committee must account for at least 52% of all nodes that participate in the consensus process.
2. PoDC Consensus Model
RepaChain’s consensus algorithm quickly generates blocks by conducting votes in the standing and steering committee that use quantum random numbers (QRN).
- In ReapChain, 48% of the operating standing committee nodes and 52% of the general nodes have selected, and each of the nodes acts as a subject and verifier of the block generation that participates in the consensus process.
1) The nodes that participate in the consensus; the percentage of the steering committee nodes is maintained at 52% or higher to monitor whether or not the continually operating standing committee nodes have produced relatively.
2) As for the selection of the consensus participant, quantum random numbers are used to relatively select and distributed to the validator nodes, and then quantum random numbers and public keys are used again to assign encrypted random number tickets. A library of hardware-dependent call functions in which an unhackable message delivery system and fast authentication and consensus are implemented and named as Quantum Random Number Management Server (Qmanager).
3) Because of the hardware-dependent characteristic of quantum random number generation, Qmanager can either exist separately from the nodes.
4) The quantum random function mechanism has adopted for the role of Qmanager and the differentiating features of the REAP CHAIN contained in the QRF mechanism.
3. QRF Mechanism for Consensus
QRF Mechanism: Consensus is established in the ReapChain by utilizing quantum random numbers, public-key encryption, and public key hash for fast recognition. A series of authentication and information transfer systems has named Quantum Random Function Mechanism. QRF provides a functional element by using a quantum random number server (Qmanager).
Qmanager holds network information and public keys of all nodes that participate in the blockchain network. The network address of Qmanager is open to all nodes. In contrast, nodes participating in the chain generate public and private keys of applicable nodes by using public key encryption specified by ReapChain, and then retain the private keys and register the public keys in Qmanager. The Qmanager has an encrypted node master table in the form of an in-memory DB and stores node ID, node network information, public key, and an assigned quantum random number.
4. Consensus Process and Block Generation
1) Block Generation
ReapChain has a basic block generation cycle of 2 seconds. But in the ReapMiddleChain, that corresponds to the temporary ledger; approvals are notified in less than 1 second to create the same effect as if consumers are receiving credit card payment through authorized notifications.
In reality, block generates within 2 seconds in ReapChain, so the consumers rarely notice any payment approval delays, and It thus makes the ReapChain suitable for commercial transaction deployment. The ReapChain can quickly reach a consensus within 2 seconds by selecting a coordinator from a standing committee that operates at all times.
It is possible because it reaches the consensus with the minimum amount of network traffic under direct communication among 28 nodes surrounding the selected coordinator during the process. Mainly, time delays for a while and inevitably network loads occur in collecting validation messages that broadcasts in P2P networks; A coordinator exchanges message only once in the internal network organization. Such a coordinator ultimately becomes a single block producer to generate a block.
If a block does not generate within 2 seconds, the block generation of the corresponding cycle skips. In the REAP CHAIN, It may require more time to reach the finality of every block, even though the block generates within brief seconds. Therefore, considerations can make to finalize the transactions after accumulating a certain number of blocks by installing checkpoints at every 20 blocks like in Ethereum Casper protocol.
2) PoDC Consensus Process
ReapChain creates one round of tables for block generation. In one round, 15 steering committee nodes have selected among the general nodes through security enhanced random selection mechanism, and 14 standing committee nodes participated together in the validation process.
The reliability of the consensus that is achieved within the REAP CHAIN’s QSN (Quantum Safety Net) have insured here.
Since the consistently operated nodes of REAP CHAIN account for 48% of all consensus nodes and the general nodes using quantum random numbers have randomly selected without prediction, chances that a ratio of malicious user nodes is at 52% continuously is statistically meager.
[Consensus Process]
[Consensus Algorithm Flowchart]
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