Blockchain Scalability and its Foundations in Distributed Systems | Week 4

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 4 Answer Coursera Quiz

Module 4 quiz

Q1. In communication synchrony, we assume two things. First, we assume that every message sent gets delivered in a maximum amount of time.
What is the second assumption?

  • This maximum amount of time is not known by the algorithm.
  • This maximum amount of time is known by the algorithm.

Answer: This maximum amount of time is known by the algorithm.

Q2. In classic blockchains, the chain can fork. What is the recommendation for users to consider that a transaction is committed?

  • To wait for 1 hour
  • To wait until they can see a number k of blocks are appended to the blockchain the block containing this transaction and where k is a parameter of the blockchain.
  • To make sure this transaction is part of the first block observed at a particular index

Answer: To wait until they can see a number k of blocks are appended to the blockchain the block containing this transaction and where k is a parameter of the blockchain.

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

Q3. We’ve looked at 8 well-known fallacies that people tend to believe about distributed systems and networking.
Regarding the network, which of the following did we learn is not true?

  • There is no single administrator.
  • It is not reliable.
  • It is homogeneous.
  • The network is not secure.

Answer: It is homogeneous.

See also  Blockchain Scalability and its Foundations in Distributed Systems | Week 2

Q4. Regarding the speed and latency of the distributed systems and networking, which of the following is not correct?

  • The network topology changes over time.
  • Bandwidth is limited.
  • Transport is costly.
  • There is no latency

Answer: There is no latency

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

Q5. True or False?
It is possible for a Byzantine node to double spend without owning a large portion of the mining power in proof of work blockchains.

  • True
  • False

Answer: True

Q6. Let E3 be a set of edges that separates the communication graph in two subgraphs with same cumulative mining power. Let an attacker delay messages on E3.
As the communication is delayed between the two subgraphs, each subgraph mines its own DAG. For an attacker who is connected to both subgraphs, he will need to mine a small number of blocks. To which subgraph(s) shall he contribute his blocks in order to double spend in this situation?

  • One subgraph
  • Both subgraphs

Answer: One subgraph

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

Q7. Let E3 be a set of edges that separates the communication graph in two subgraphs G1 and G2 with the same cumulative mining power. What should an attacker with a low mining power do to execute the Balance Attack?

  • Mine blocks in both subgraphs
  • Delay messages in E3
  • Delay messages in E1
  • Mine blocks in one subgraph only
  • Issue a transaction in the subgraph where the attacker did not mine blocks
See also  Blockchain Scalability and its Foundations in Distributed Systems | Week 1

Answer: Delay messages in E3
Mine blocks in one subgraph only
Issue a transaction in the subgraph where the attacker did not mine blocks

Q8. Network attacks that enable to intercept messages in the network are often called what?

  • Sybil Attack
  • Man-in-the-middle attack
  • Rosenfeld’s attack
  • 51% attack

Answer: Man-in-the-middle attack

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

Q9. True or False
Ethereum is vulnerable to man-in-the-middle attacks when run in a consortium environment.

  • True
  • False

Answer: True

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

Q10. True or False?
It is impossible for the Balance Attack to succeed against Ethereum when the attacker has less than 1% of the mining power.

  • True
  • False

Answer: False

These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

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These are Blockchain Scalability and its Foundations in Distributed Systems Week 4 Answer Coursera Quiz

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