Byzantine Fault Tolerant (BFT) Mechanisms BDC Practice Questions (Page 3)

Questions 11–15

1. 11foundation · medium

   In a Byzantine fault-tolerant system, what does the property of 'safety' guarantee?

   • AAll messages are delivered within a bounded time.
   • BThe system can tolerate up to one-third of nodes being faulty.
   • CNo two honest nodes will decide on conflicting values.
   • DThe system will eventually make progress and reach a decision.
   Reveal Solution Discussion Select an answer first
2. 12foundation · medium

   In the PBFT algorithm, what is the purpose of the 'pre-prepare' phase?

   • ATo send the result of the executed request back to the client.
   • BTo assign a sequence number to a proposed request and broadcast it to all replicas.
   • CTo detect and replace a faulty primary node.
   • DTo collect votes from replicas to confirm that a request has been executed.
   Reveal Solution Discussion Select an answer first
4. 13application · medium

   In a PBFT-based blockchain, a replica receives a pre-prepare message for block X from the primary, but the message is not signed correctly. What should the replica do?

   • AAccept the message and proceed to the prepare phase, as long as the block content is valid.
   • BBroadcast the message to other replicas to verify if it is valid.
   • CRequest a new primary immediately.
   • DIgnore the message and do not enter the prepare phase for block X.
   Reveal Solution Discussion Select an answer first
5. 14application · medium

   A network architect is evaluating PBFT for a permissioned blockchain with 50 validator nodes. The team is concerned about the communication overhead. What is the primary scalability limitation of PBFT in this context?

   • APBFT cannot handle network partitions
   • BPBFT requires a trusted third party to coordinate
   • CPBFT can only tolerate a maximum of 5 faulty nodes
   • DEvery replica broadcasts messages to all other replicas, leading to O(n^2) message complexity
   Reveal Solution Discussion Select an answer first
6. 15expert · hard

   A team is designing a new BFT consensus protocol for a permissioned network with 100 nodes. They need to choose between a leader-based protocol (like HotStuff) and a leaderless protocol (like SBFT). The network has high transaction volume and requires low latency. Which protocol is more suitable and why?

   • AHotStuff, because it has linear communication complexity and is optimized for high throughput
   • BNeither can handle 100 nodes
   • CBoth are equally suitable
   • DSBFT, because it eliminates the leader bottleneck
   Reveal Solution Discussion Select an answer first