CBCP Consensus Mechanisms 5 — Questions and Answers
Question 1: What is 'fork choice rule' and why is it essential in blockchain consensus?
- A governance mechanism for upgrading protocol rules
- An algorithm nodes use to determine which chain branch to follow when multiple valid chains exist (Correct answer)
- A method for merging two competing blockchains
- A rule that determines when miners must switch mining pools
Correct answer: An algorithm nodes use to determine which chain branch to follow when multiple valid chains exist
The fork choice rule provides a deterministic way for all nodes to independently select the same canonical chain from competing branches, maintaining network-wide agreement.
Question 2: In Algorand's consensus, what is a 'committee' and how is it selected?
- A fixed group of 21 elected block producers voted in by token holders
- A randomly and privately selected group of validators chosen via VRF proportional to stake (Correct answer)
- A governance board that approves protocol changes
- A set of nodes that validate smart contracts only
Correct answer: A randomly and privately selected group of validators chosen via VRF proportional to stake
Algorand uses a VRF-based cryptographic sortition to randomly and privately select a committee each round, with selection probability proportional to each node's stake.
Question 3: What is the CAP theorem's relevance to blockchain consensus design?
- It proves blockchain networks can achieve all three properties simultaneously
- It states distributed systems cannot simultaneously guarantee Consistency, Availability, and Partition tolerance — forcing design trade-offs (Correct answer)
- It establishes the minimum capital required for network security
- It defines the maximum transaction capacity of any consensus system
Correct answer: It states distributed systems cannot simultaneously guarantee Consistency, Availability, and Partition tolerance — forcing design trade-offs
The CAP theorem forces blockchain designers to choose trade-offs: BFT protocols often favor Consistency and Partition tolerance while sacrificing some Availability during faults.
Question 4: What distinguishes 'synchronous' from 'asynchronous' network models in consensus protocol design?
- Synchronous networks use TCP while asynchronous networks use UDP
- Synchronous models assume bounded message delays; asynchronous models assume no timing guarantees (Correct answer)
- Synchronous consensus requires more validators than asynchronous consensus
- Asynchronous networks always achieve faster finality
Correct answer: Synchronous models assume bounded message delays; asynchronous models assume no timing guarantees
Synchronous models allow protocols to rely on known time bounds for message delivery, while asynchronous models (more realistic) cannot assume any timing, making consensus design harder.
Question 5: In Proof of Space (PoSpace) or Proof of Capacity, what resource do validators compete on?
- Network bandwidth and uptime
- Available disk space used to store precomputed cryptographic plots (Correct answer)
- RAM speed and CPU cache size
- Number of transactions previously validated
Correct answer: Available disk space used to store precomputed cryptographic plots
Proof of Space requires nodes to pre-fill their disk storage with cryptographic data (plots); nodes with more allocated space have proportionally higher chances of winning block creation rights.
Question 6: What is 'checkpoint finality' as used in Ethereum's Casper FFG protocol?
- Every transaction is individually finalized as it is included in a block
- Validators vote to finalize specific epoch boundary blocks, making them irreversible once 2/3 supermajority is reached (Correct answer)
- Miners checkpoint their work every 100 blocks to prevent reorgs
- A committee finalizes blocks based on the longest PoW chain rule
Correct answer: Validators vote to finalize specific epoch boundary blocks, making them irreversible once 2/3 supermajority is reached
Casper FFG finalizes 'checkpoint' blocks at epoch boundaries when validators cast source-to-target votes achieving a 2/3 supermajority, making those blocks economically irreversible.
Question 7: What is a 'Sybil attack' and which consensus mechanisms are inherently designed to resist it?
- A smart contract exploit; resisted by formal verification
- Creating many fake identities to gain disproportionate influence; resisted by PoW and PoS through costly resource requirements (Correct answer)
- A 51% hash rate takeover; resisted by DPoS voting
- Flooding the network with transactions; resisted by fee mechanisms
Correct answer: Creating many fake identities to gain disproportionate influence; resisted by PoW and PoS through costly resource requirements
Sybil attacks involve creating multiple fake nodes to manipulate consensus; PoW and PoS resist this by requiring real-world costly resources (hash power or staked capital) to participate meaningfully.
CBCP Consensus Mechanisms 5
What is 'fork choice rule' and why is it essential in blockchain consensus?