If more than 51% of the bitcoin network’s hash power is controlled by one node, the blockchain can be destroyed bringing the whole protocol to an end. This was described by Satoshi Nakamoto as the “51% attack” which is one of the potential risks that can sabotage the bitcoin network.

The proof-of-work POW concept of the bitcoin network is crucial for maintenance of the security of the blockchain. Satoshi utilized a binomial random walk model that proved that malicious attackers have to control at least 51% of the network’s hashing power before they can succeed in achieving this attack to generate fraudulent transactions that can disrupt the blockchain. Despite the fact that it is highly unlikely for a single node to be able to control more than 51% of the network’s hashing power, the network’s overall hashing power is technically controlled by a small number of major nodes ( as shown by the below figure). This phenomenon is known as centralization of computing power.

computing power distribution.PNG

computing power distribution.PNG

A group of researchers from China published a paper that proposed a new POW mechanism that shields the bitcoin network against the risks of a 51% attack, especially that the current POW design can lead to centralization of hashing power across the network.

A New PoW Mechanism Based On The Concept of Partial Solutions:

According to bitcoin’s current design, miners have to discover a 32 bit nonce which would cause its hash to be part of a given target. Once a miner has found a valid once, he/she can submit a newly formed block. This aspect of the bitcoin protocol can be labeled as “Winners get all”. Miners who control greater amount of computing power will have bigger chances to participate in the creation of the chain with the longest consensus, which would create another phenomenon that we can label as “Richer becomes richer”.

If a block’s problem has more than one solution, it is possible to record the efforts made by Miner i to find a solution within a specific time window. This would permit selecting multiple miners rather than one, which would establish a principle that we can label as “Career open to all talents, without distinction of birth”.

The authors of the paper introduced a new concept of “Partial solutions”, where every miner’s work across the network can be monitored and appreciated. This gives rise to a new principle that the authors called “Distribution according to labor”. The new randomness source introduced throughout the new protocol gives each and every node an equal chance to be the node reporting the block. This will render a 51% attack an impossible task to accomplish, because the chance of reporting a block is irrelevant to the computing power of the mining node. This will not discourage miners to contribute their processing power as nodes possessing great computing power will be able to earn more rewards when they contribute more computing power. This new mechanism will consider “reporting right” as some kind of “political power”, while “computing power” will be considered as a form of “economic power”. The new protocol prevents miners possessing greater economic power from having also greater political power; a concept that the authors of the paper called “All men are created equal”.

On the other hand, when every node has an equal chance to report a block, this may increase the liability of Sybil attacks. A Sybil can fake numerous malicious nodes that require little costs, but increase the chances for receiving block reporting rights. To alleviate the risks of Sybil attacks, the researchers introduced a parameter c which will markedly increase the costs of an attack. Accordingly, not every participating node will have reporting rights, but only those who have accomplished more than c * N solutions. The authors of the paper called this “The People’s Congress Mechanism”.

Implementation Details Of the New PoW Mechanism:

To deploy the proposed protocol, two new issues have to be implemented:

1- A new puzzle design. This can be achieved via reducing the original difficulty of the bitcoin nonce problem, while setting the value of N within the context of the same rule to ensure a constant rate of bitcoin output.

2- counter. It is critical to count i for every miner. The counter should be designed to be smart enough to omit duplicate solutions and store only the correct ones. This will be highly dependent on the new puzzle design.

Double spending attacks and the 51% attack are major risks endangering the bitcoin protocol. Implementation of the new PoW we presented can totally prevent the 51% attack

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