Byzantine Fault Tolerant (BFT) Mechanisms BDC Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A blockchain team is comparing Tendermint and PBFT for a new proof-of-stake network. They need a consensus protocol that provides immediate finality and can be integrated with a public blockchain where validators are selected based on stake. Which protocol is the better fit and why?

   • APBFT, because it is more efficient in public networks with many validators
   • BTendermint, because it tolerates up to half of the validators being Byzantine
   • CTendermint, because it is designed for proof-of-stake and provides immediate finality through its BFT consensus
   • DPBFT, because it does not require a round-robin leader selection
   Reveal Solution Discussion Select an answer first
2. 2expert · hard

   A public blockchain is considering adopting a BFT-based consensus protocol instead of Proof of Work. The network has thousands of nodes, and anyone can join or leave. Which challenge is most critical for applying BFT in this public setting?

   • AThe requirement for a central authority
   • BThe lack of cryptographic primitives
   • CThe inability to tolerate any Byzantine faults
   • DThe need for a known and relatively stable set of validators
   Reveal Solution Discussion Select an answer first
4. 3application · medium

   A permissioned blockchain network currently uses PBFT with 20 validator nodes. The network is experiencing high latency and low throughput due to the consensus protocol. The team is considering moving to a different BFT variant to improve performance. Which change would most directly reduce the communication overhead in each consensus round?

   • ASwitch to a protocol that uses a linear communication pattern, such as HotStuff.
   • BReduce the block size to decrease the amount of data in each message.
   • CIncrease the number of validator nodes to 30 to spread the load.
   • DUse a crash fault tolerant protocol like Raft instead.
   Reveal Solution Discussion Select an answer first
5. 4application · medium

   A permissioned blockchain network uses PBFT to reach consensus. During a round, a replica receives a valid pre-prepare for block B, then collects 2f+1 prepare messages for block B. What is the next step in the PBFT protocol?

   • ABroadcast a commit message for block B to all other replicas.
   • BExecute the block and update the local state.
   • CSend a prepare message to the primary to confirm receipt.
   • DWait for 2f+1 commit messages before doing anything else.
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   A system architect is designing a distributed database for a financial exchange. The system must tolerate nodes that crash and also nodes that may send corrupted data due to software bugs. The architect is deciding between a CFT algorithm (like Raft) and a BFT algorithm (like PBFT). What is the key trade-off to consider?

   • ACFT provides stronger fault tolerance than BFT
   • BCFT requires more nodes than BFT
   • CBFT is always faster than CFT
   • DBFT provides stronger fault tolerance but requires more nodes and higher communication overhead
   Reveal Solution Discussion Select an answer first