NPTEL Blockchain and its Applications Week 6 Assignment Answers 2025
1. What is/are the primary distinction between crash faults and Byzantine faults?
a. Crash faults involve deliberate malicious behavior
b. Byzantine faults involve deliberate malicious behavior
c. Crash faults require at least 3F + 1 node for consensus (here, F is the number of crash faults)
d. Byzantine faults can never partition the network
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2. Suppose you execute your tasks distributedly from four different systems at four different locations. To maintain the consensus among the systems, you are using the BFT model. You found that one system is permanently failed due to a hardware fault and another system is compromised by an attacker. Does your system correctly work at all?
a. No
b. Yes, with the remaining nodes
c. Yes, with all the nodes
d. Yes, but with reduced efficiency
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3. In Paxos, what will a proposer do if it receives a promise containing an already accepted value?
a. Use the previously accepted value with the highest ID
b. Propose a completely new value
c. Abort the consensus
d. Ignore the promise and continue
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4. Which of the following is/are true regarding the permissioned blockchain model?
a. Users are anonymous
b. Transactions are publicly visible to everyone
c. Users are authenticated through a Membership Service Provider (MSP)
d. Security and consensus are required
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5. In the Paxos algorithm, a majority of promises ensure:
a. Agreement on the ID, value
b. Liveness of the system
c. Safety against conflicting proposals
d. Disagreement on the ID, value
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6. If there are 3 faulty nodes, at least how many nodes are needed to reach consensus in the Byzantine Fault Tolerance (BFT) system?
a. 4
b. 8
C. 7
d. 10
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7. Which of the following is/are true regarding a consensus when there is one good commander, one good lieutenant, and one faulty lieutenant in a Byzantine Generals Problem.
a. Consensus is always possible
b. Consensus is not possible because the faulty lieutenant can mislead
c. Consensus is not possible because the commander can mislead
d. Consensus will be possible if there are additional good lieutenants
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8. What is/are the purpose of Multi-Paxos?
a. To have a termination guarantee
b. To execute smart contracts on multiple blockchains
c. To reach a consensus for a series of values
d. To prioritize liveness over safety
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9. Which of the following is/are false regarding classic Paxos?
a. It requires a majority of acceptors to proceed
b. It achieves consensus on ID and not the value
c. It achieves consensus on the value and not ID
d. It can work with Byzantine faults
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10. In Paxos, which of the following is/are true about the roles of nodes?
a. A node cannot play more than one role
b. A proposer node cannot become a learner
c. A node can play one or more than one role
d. An acceptor node cannot become a learner
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