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Consensus Mechanisms and Mining Flashcards

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  1. What is a '51% attack' in the context of Proof of Work blockchains?

    Answer: When a miner controls more than half the network's hash rate and can rewrite recent transactions

    If a single entity controls >50% of hash rate, they can mine blocks faster than the rest of the network combined, enabling double-spend attacks.

  2. In Proof of Stake, what is 'slashing'?

    Answer: A penalty that destroys a portion of a validator's staked funds for malicious behavior

    Slashing is a punitive mechanism where validators lose part of their stake if they act dishonestly, such as double-signing blocks.

  3. What distinguishes Delegated Proof of Stake (DPoS) from standard Proof of Stake?

    Answer: Token holders vote for a limited set of delegates who validate transactions on their behalf

    In DPoS, token holders vote for a small group of elected delegates (e.g., 21 in EOS) who produce blocks, making consensus more efficient.

  4. What is the 'nothing-at-stake' problem in early Proof of Stake designs?

    Answer: Validators could cheaply vote on multiple competing chain forks without any cost, undermining consensus

    Unlike PoW where mining one fork costs real energy, early PoS validators could sign every fork for free, making double-spends easier.

  5. Which consensus algorithm does Ripple (XRP) use?

    Answer: Ripple Protocol Consensus Algorithm (RPCA) with a Unique Node List

    Ripple uses its own federated consensus where trusted validator nodes on a Unique Node List (UNL) agree on transaction ordering.

  6. What is 'mining difficulty adjustment' in Bitcoin and how often does it occur?

    Answer: An automatic recalibration of the target hash every 2016 blocks (~2 weeks) to maintain a ~10-minute block time

    Bitcoin's protocol adjusts the proof-of-work target every 2016 blocks so that blocks continue to be found approximately every 10 minutes regardless of total hash rate.

  7. What is 'uncle blocks' (ommers) in Ethereum's original PoW system?

    Answer: Valid blocks that were mined simultaneously with the main chain block but not included in the canonical chain

    Uncle blocks are valid PoW solutions found at the same time as a canonical block; Ethereum rewarded miners for these to reduce centralization pressure from fast block times.