Selfish Mining in PoW Systems

Overview

Selfish mining is a strategic attack or mining technique that can be employed by a group of miners in a blockchain network, particularly in those using Proof of Work (PoW) consensus algorithms like Bitcoin’s.

The goal of selfish mining is to gain an unfair advantage over other miners and increase the attacker’s chances of earning more mining rewards. It was first introduced in a research paper by Ittay Eyal and Emin Gün Sirer in 2013.

The Attack: How it happens

1. Private Mining: Instead of immediately broadcasting mined blocks to the network, selfish miners keep newly mined blocks private.
2. Mining Secret Branch: While keeping their blocks private, selfish miners continue to mine on top of their own block, creating a separate, secret branch of the blockchain. This secret branch is not visible to the rest of the network.
3. Race Condition: When the selfish miners discover a new block on their secret branch, they wait for a certain amount of time to see if the rest of the network discovers a competing block. If another miner discovers a block during this time, the selfish miners switch to mining on the public blockchain.
4. Double Spend Attack: If the selfish miners’ secret branch becomes longer than the public blockchain due to their mining power, they can then release their private chain to the network. This reorganization of the blockchain can potentially invalidate the transactions in the blocks they kept private. They can, therefore, double-spend their cryptocurrency, causing financial losses to other network participants.

Example of Selfish Mining

Here’s a simplified example of how selfish mining might work in a Proof of Work (PoW) blockchain like Bitcoin:

Suppose we have a blockchain network with two miners: the honest miner (Miner A) and the selfish miner (Miner B).

1. Mining Competition Starts:
   • Both Miner A and Miner B start mining on the network and attempt to solve the PoW puzzle to create a new block.
2. Miner B Finds a Block:
   • Miner B successfully mines a new block but decides not to broadcast it immediately to the network. Instead, Miner B keeps the block private.
3. Public Chain Continues:
   • While Miner B’s block remains private, the public blockchain continues to grow with transactions and blocks mined by other honest miners. Miner A mines the next block on the public chain.
4. Secret Chain Grows:
   • Miner B continues to mine on top of their own secret block, creating a separate, hidden chain known only to them.
5. Race Condition:
   • At this point, Miner B faces a decision. They can choose to reveal their secret chain to the network, attempting to replace the public chain with their longer secret chain.
6. Releasing the Secret Chain:
   • If Miner B’s secret chain becomes longer than the public chain, they release it to the network. This causes a chain reorganization, where the blockchain switches to the longer chain created by Miner B.
7. Double Spend Attack:
   • The transactions in the blocks of the original public chain are invalidated, allowing Miner B to double-spend their cryptocurrency, as those transactions are no longer part of the main chain.
8. Profit for Miner B:
   • Miner B earns the mining rewards for the blocks on their secret chain and successfully double spends some cryptocurrency, gaining an unfair advantage and financial benefit.

It’s important to note that this is a simplified example for illustrative purposes. In practice, selfish mining is more complex, and the success of such an attack depends on various factors, including the mining power of the selfish miner relative to the rest of the network. The key to selfish mining is the strategic timing of when to reveal the secret branch to maximize the chances of reorganizing the blockchain in their favor.

Selfish mining can be a profitable strategy for miners who have a significant amount of mining power and can launch coordinated attacks. However, it is important to note that selfish mining is considered a malicious activity and goes against the principles of fairness and security in blockchain networks.

Remediation

Remediating selfish mining and related attacks in a Proof of Work (PoW) blockchain network involves implementing countermeasures and making protocol adjustments to discourage or prevent such malicious behavior. Here are some steps that can be taken to address selfish mining and its risks:

1. Network Propagation Improvements:
   • Improve the efficiency and speed of block and transaction propagation across the network to reduce the advantage of selfish miners.
   • Implement better communication protocols and techniques to ensure that new blocks are quickly disseminated to all nodes.
2. Longer Confirmation Times:
   • Increase the number of confirmations required for transactions to be considered final. This makes it more difficult for selfish miners to execute successful double-spend attacks.
3. Incentives for Honest Mining:
   • Adjust the mining reward structure or penalties to incentivize miners to follow the rules honestly.
   • Implement penalties or disincentives for miners who engage in selfish mining or double-spending.
4. Frequent Block Broadcasts:
   • Encourage miners to broadcast their mined blocks as soon as possible, reducing the chances of a secret branch becoming longer than the public blockchain.
5. Network Upgrades:
   • Consider protocol upgrades to address vulnerabilities specific to selfish mining and other attacks.
   • Introduce changes to the consensus algorithm or rules that make selfish mining less profitable or feasible.
6. Increased Network Hashrate:
   • Encourage more miners to participate in the network to increase its overall hash rate. A higher hash rate makes it more challenging for a single entity or group to execute selfish mining attacks successfully.
7. Active Monitoring and Analysis:
   • Continuously monitor the network for signs of selfish mining or other malicious activities.
   • Analyze network behavior and look for patterns that may indicate an ongoing attack.