Blockchain and its Applications | NPTEL | Week 6 Assignment Solutions

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Blockchain and its Applications NPTEL Week 6 Assignment Solutions

Q1. If there are 24 faulty nodes (crash fault) in asynchronous CFT, at least how many nodes needed to reach consensus.

a) 48
b) 49
c) 50
d) 51

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Q2. In Paxos, a node can have only one role among the three roles at a time. True or False

a) False
b) True

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Q3. Can we reach a consensus when there is one commander, one good lieutenant, and one faulty lieutenant in a Byzantine Generals Problem. Yes or No?

a) Yes
b) No

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Q4. If there are 24 faulty nodes in, at least how many needed to reach consensus in the Byzantine Fault Tolerance (BFT) system.

a) 72
b) 73
c) 48
d) 49

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Q5. Which are the examples of the synchronous consensus techniques?

a) RAFT
b) PAXOS
c) Byzantine General Model
d) Practical Byzantine General Model

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Blockchain and its Applications NPTEL week 6 Assignment Solutions

Q6. Suppose you execute your tasks distributedly from six different locations. For maintaining 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 will all the nodes

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Q7. Which of the statements are true?

a) Paxos is based on state-machine replication
b) In Paxos, Proposers and Learners maintain a state of the running epochs
c) In a Paxos, once a consensus is reached, Paxos cannot progress to another consensus
d) Paxos works in two rounds

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Blockchain and its Applications NPTEL week 6 Assignment Solutions

Q8. State machine replication-based consensus is used over permissioned blockchains.
Select the suitable reason(s)?

a) The network is closed, and the nodes know each other, hence state replication is possible among the known nodes
b) Not need to spend power, time, or bitcoin
c) Machines can behave maliciously, hence consensus in required
d) State machine replication-based consensus is not recommended to use over permissioned bloackchains

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Blockchain and its Applications NPTEL week 6 Assignment Solutions

Q9. Which are the properties of an asynchronous consensus:

a) Validity
b) Agreement
c) Termination
d) Integrity

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Q10. The following code snipper from paxos algorithm belongs to which phase?
is the ID the largest I have seen so far, max_id == N?
if yes
reply with an ACCEPTED message & send ACCEPTED(ID, VALUE) to all learners
if no
do not respond (or respond with a “fail” message)

a) PREPARE-PROMISE
b) PROPOSE-ACCEPT

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Blockchain and its Applications NPTEL week 6 Assignment Solutions

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