Blockchain Scalability and its Foundations in Distributed Systems | Week 2

Course Name: Blockchain Scalability and its Foundations in Distributed Systems

Course Link: Blockchain Scalability and its Foundations in Distributed Systems

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Module 2 quiz

Q1. Leslie Lamport once said “A distributed system is one in which the failure of a computer you didn’t even know existed can render your own computer unusable.”
In the context of distributed computing, what does this quote indicate? (There may be more than one correct answer).

  • Computer support is essential for proper functioning.
  • Your computer’s functions are being controlled by an unknown other.
  • Users are working in a system with multiple nodes that can impact on their experience.
  • A distributed system is a single system in a user’s perspective.

Answer: Users are working in a system with multiple nodes that can impact on their experience.
A distributed system is a single system in a user’s perspective.

Q2. What type of failure is most serious?

  • Crash failure
  • Arbitrary failure

Answer: Arbitrary failure

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q3. Regarding crash failure, which of the following statements is correct?

  • It happens when a node can send the wrong message.
  • A node can send and receive a message before it halts.
  • A node can interact as normal after it halts.

Answer: A node can send and receive a message before it halts.

Q4. Regarding arbitrary (a.k.a. Byzantine) failure, which of the following statements is NOT correct?

  • Node behavior is predictable.
  • Node can fake a crash failure.
  • Node can flood the network with messages.
  • Node can send messages that may be outside the domain specification.
  • Node can send or receive messages according to normal patterns.
See also  Blockchain Scalability and its Foundations in Distributed Systems | Week 4

Answer: Node behavior is predictable.

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q5. “Any decided value is a proposed value”.
Which consensus property is best described by this statement?

  • Termination
  • Agreement
  • Validity

Answer: Validity

Q6. Consider the following distributed execution:
Does this distributed execution solve consensus?

  • No
  • Yes

Answer: Yes

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q7. According to Fisher, Lynch and Patterson (1985), there is no solution to the consensus problem among n nodes if:
(There may be more than one correct answer)

  • There is at least one failure.
  • There is an assumption on the speed it takes to deliver a message.
  • There is no assumption on the time it takes to deliver a message.
  • There is no failure.

Answer: There is at least one failure.
There is no assumption on the time it takes to deliver a message.

Q8. Which impossibility study shows that there is no solution to the consensus problem among n nodes if the number of Byzantine nodes is greater than or equal to a third of all nodes that are trying to solve consensus?

  • Fisher, Lynch and Patterson (1985)
  • Pease, Schostak and Lamport (1980)
  • Castro and Liskov (2002)

Answer: Pease, Schostak and Lamport (1980)

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q9. According to Pease, Schostak and Lamport (1980), there is no solution to the consensus problem among n nodes if the number of _______ nodes is greater than or equal to a third of the entire set of nodes that are trying to solve consensus.

  • Byzantine
  • Crash
  • Either of these two types of node failure.
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Answer: Byzantine

Q10. Which of the following attacks occurs when a malicious Byzantine node creates fake, faulty nodes to the point where the number of faulty nodes exceed a third of the entire set of nodes?

  • Sybil attack
  • 51% attack
  • Finney’s attack

Answer: Sybil attack

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q11. A malicious Byzantine miner mines until it has a branch longer than the ones created by correct miners in the system. Eventually, as the particular system selects the longest branch, the Byzantine miner will have the ability to impose its blocks and the set of transactions it has chosen. The branch that contains blocks created by the correct miners will therefore be discarded.
Which of the following attacks best describes the scenario above?

  • Sybil attack
  • 51% attack
  • Finney’s attack

Answer: 51% attack

Q12. A cryptopuzzle is implemented when a miner is given a block and a threshold. A miner will then repeatedly select a nonce and apply a pseudo-random function to this block and the selected nonce. How does the miner know when they have solved the cryptopuzzle?

  • They have obtained a result lower than the threshold.
  • They have obtained a result higher than the threshold.

Answer: They have obtained a result lower than the threshold.

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q13. In order to resolve a fork and maintain a single chain, which nodes in the network apply the strategy to choose the particular block that is at each index of the chain.

  • The miners
  • All the nodes
  • The nodes with the greatest computational powers
See also  Blockchain Scalability and its Foundations in Distributed Systems | Week 3

Answer: All the nodes

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q14. Which of the following problems related to selecting the longest branch does the GHOST protocol seek to address?

  • Sybil attack
  • Propagation delay of blocks
  • Rosenfeld’s attack

Answer: Propagation delay of blocks

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

Q15. Ethereum (as well as the upcoming Ethereum 2.0) consensus is inspired by the GHOST protocol. However, GHOST is different from the existing Ethereum algorithm.
What does GHOST take into account that Ethereum does not?

  • Depth of chain
  • Number of descendants for each block

Answer: Number of descendants for each block

These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

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These are Blockchain Scalability and its Foundations in Distributed Systems Week 2 Answer Coursera Quiz

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