Blockchain Developer Consensus Mechanisms 3

Question 1

What is a 'long-range attack' in Proof of Stake?

Accepted Answer

Rewriting history from an old block using past validator keys

Answer

Attackers use old validator keys to build an alternative chain from far back in history.

Question 2

In Proof of Work, what is the role of the 'difficulty' parameter?

Accepted Answer

It adjusts how hard it is to find a valid block hash

Answer

Difficulty adjusts the target hash threshold to keep block times roughly constant.

Question 3

Which attack involves a miner secretly mining a longer chain then releasing it to reverse transactions?

Accepted Answer

51% attack

Answer

A 51% attack uses majority hash power to build and reveal a longer chain that reorganizes the ledger.

Question 4

What does a VRF (Verifiable Random Function) provide in consensus protocols like Algorand?

Accepted Answer

Unpredictable yet verifiable random leader selection

Answer

A VRF generates randomness that is unpredictable in advance but publicly verifiable afterward, used for secret committee selection.

Question 5

In Practical Byzantine Fault Tolerance (PBFT), what are the three main phases?

Accepted Answer

Pre-prepare, prepare, commit

Answer

PBFT reaches agreement through pre-prepare, prepare, and commit message rounds among replicas.

Blockchain Practice Test