Consensus Mechanisms Flashcards

What is 'fork choice rule' and why is it essential in blockchain consensus?

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.

In Algorand's consensus, what is a 'committee' and how is it selected?

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.

What is the CAP theorem's relevance to blockchain consensus design?

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.

What distinguishes 'synchronous' from 'asynchronous' network models in consensus protocol design?

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.

In Proof of Space (PoSpace) or Proof of Capacity, what resource do validators compete on?

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.

What is 'checkpoint finality' as used in Ethereum's Casper FFG protocol?

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.

What is a 'Sybil attack' and which consensus mechanisms are inherently designed to resist it?

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.