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Dev Release 16

April 24, 2024

Greetings BlockDAG community!

As we continue fortifying BlockDAG's security, let's delve into the realm of consensus mechanisms. These protocols are the lifeblood of our trustless environment, ensuring nodes adhere to the rules and preventing collusion. Our objective: identify the ideal consensus mechanism for BlockDAG.

Core Considerations

  • Byzantine Fault Tolerance (BFT): The mechanism must guarantee the BlockDAG ledger's immutability and integrity even in asynchronous Byzantine environments where nodes can fail or exhibit malicious behavior.
  • Scalability: The chosen approach should support high transaction throughput without sacrificing performance. Throughput should ideally scale linearly with the number of participating nodes.
  • Energy Efficiency: Minimizing energy consumption aligns with our commitment to sustainability. We need a mechanism that offers low computational overhead for node operation.
  • Decentralization: We target a distributed network where no single entity holds disproportionate power. The consensus mechanism should promote a fair and permissionless environment.

Candidate Consensus Mechanisms: Proof of work (PoW)

  1. Proof of Work (PoW):
  • Concept: The pioneering approach of Bitcoin. Miners compete to solve a computationally intensive cryptographic puzzle. The winning miner adds the next block and receives a block reward.
  • Security: Relies on the network's combined hashing power. Attackers would require more than 51% of the hashing power to manipulate the BlockDAG ledger.
  • Limitations: Energy consumption for mining raises concerns about scalability and sustainability. Additionally, PoW's block finality can be slow due to the probabilistic nature of block acceptance.

Technical Details:

  • Hashing Algorithm: Secure hash functions like SHA-256 are employed to generate unique block identifiers that are sensitive to any changes in the block data.
  • Difficulty Adjustment: The mining difficulty is dynamically adjusted to maintain a desired block generation rate. This ensures a balance between security and efficiency.

Algorithm behind PoW:

  • Nodes receive a new transaction.
  • Miners bundle transactions into a block candidate.
  • A hash function (like SHA-256) is used to generate a unique hash for the block header, which includes the previous block's hash and the bundled transactions.
  • Miners modify a nonce value within the block header until the hash meets a specific difficulty requirement (e.g., starting with a certain number of leading zeros). This process requires significant computational power.
  • The first miner to find a valid hash broadcasts the block to the network.
  • Other nodes verify the block's hash and transaction validity.
  • If a majority of nodes accept the block, it's added to the blockchain, and the winning miner receives a reward.

Proof of Stake (PoS)

Proof of Stake (PoS):

  • Concept: Block validators are chosen probabilistically based on their token stake. Validators with larger stakes have a higher chance of being selected. Malicious behavior leads to stake slashing (loss).
  • Security: Economic incentives disincentivize validator misconduct. Attackers would need to acquire a significant stake to attempt a double-spend attack.
  • Benefits: More energy-efficient compared to PoW due to the absence of computationally expensive mining. Faster block finality compared to PoW.
  • Drawbacks: Security might be weaker than PoW for large-scale attacks, especially if the stake distribution is concentrated.

Technical Details:

  • Randomness Beacon: A verifiable random number generator (VRF) or other source of randomness is crucial for selecting validators in a fair and unpredictable manner.
  • Slashing Conditions: The consensus mechanism should clearly define the slashing conditions for validator misconduct (e.g., double-signing, equivocation).

Algorithm behind PoS:

  • Nodes submit transactions to the network.
  • Validators are selected based on a weighted random process, with the weight proportional to their stake.
  • Selected validators propose new blocks containing validated transactions.
  • Other nodes verify the block's validity and the validator's eligibility (sufficient stake).
  • If a majority of nodes agree on the block, it's added to the blockchain.
  • Validators who propose valid blocks receive a reward.

Nominated Proof-of-Stake (NPoS)

Nominated Proof-of-Stake (NPoS):

  • Concept: Builds on PoS by introducing token holder nominations. Token holders nominate validators they trust, and the stake of both validators and nominators is slashed for misbehavior.
  • Security: Enhanced security compared to PoS by aligning validator and nominator incentives. Malicious validators not only lose their stake but also cause nominators to lose theirs.
  • Complexity: Introduces additional layers compared to PoS, potentially increasing message overhead.

Technical Details:

  • Nomination Game Theory: The nomination scheme should be carefully designed to incentivize rational token holders to nominate honest and competent validators.
  • Reputation Systems: Reputation mechanisms can be integrated to inform token holders' nomination decisions and promote the selection of trustworthy validators.

Algorithm behind NPoS:

  • Nodes submit transactions to the network.
  • Token holders nominate validators they trust, staking tokens on their behalf.
  • Validators are chosen based on a combination of their own stake and the stake nominated on them.
  • Selected validators propose new blocks containing validated transactions.
  • Other nodes verify the block's validity, validator's eligibility, and nominator's stake.
  • If a majority of nodes agree on the block, it's added to the blockchain.
  • Validators and nominators who contribute to valid blocks receive rewards. In case of misbehavior, both parties lose their stake.

Delegated Proof of Stake (DPoS)

Delegated Proof of Stake (DPoS):

  • Concept: Token holders elect a fixed number of delegates (witnesses) to validate transactions. These delegates are responsible for proposing and voting on new blocks.
  • Security: Relies on the reputation of elected delegates and the ability of voters to switch delegation if necessary.
  • Centralization Risk: A smaller set of validators might reduce decentralization compared to PoS or NPoS.

Technical Details:

  • Delegation Mechanisms: Secure and efficient mechanisms are needed for token holders to delegate their voting power to chosen delegates.
  • Byzantine Fault Tolerance (BFT) Sub-protocols: Depending on the specific DPoS variant, BFT sub-protocols like Practical Byzantine Fault Tolerance (PBFT) might be employed to ensure finality even in Byzantine fault environments.

Algorithm behind DPoS:

  • Nodes submit transactions to the network.
  • Token holders participate in a voting process to elect a fixed number of delegates (witnesses).
  • Elected delegates are responsible for proposing and validating new blocks.
  • Other nodes verify the block's validity and the delegate's eligibility (elected status).
  • If a majority of nodes agree on the block, it's added to the blockchain.
  • Elected delegates who propose valid blocks receive rewards. Voters can switch their delegation if they're unhappy with a delegate

Next steps & conclusion

We've meticulously examined various consensus mechanisms, keeping BlockDAG's unique requirements in mind. While a definitive decision is yet to be made, this analysis equips us with valuable insights to guide our selection process. We'll continue to evaluate these mechanisms, potentially conduct simulations and testbeds, and actively solicit developer community . We'll keep you updated on our progress and the final consensus mechanism chosen for BlockDAG

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