Blockchain and its Applications | Week 2
Course Name: Blockchain and its Applications
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These are Blockchain and its Applications Assignment 2 Answers
Q1. Let Bob wants to send a long message to Alice. Alice should be able to confirm that it was indeed sent by Bob, and Bob later cannot deny that he had sent the message. They also want that nobody else should be able to see its content. Alice and Bob plan to use public key cryptography and cryptographic hashing techniques. Let the key pairs of Alice and Bob be (Pub A, Pri A) and (Pub B, Pri B), respectively.
Let E, D and H be the encryption, decryption and hash functions, respectively. Let M denote the Message and H(M) its digest. Which of the following describes the correct order of steps to be used by Alice to send the digitally signed message.
i. At Bob : M’ = E(M, KpubA)
ii. At Alice : M = E(M’, Kpria)
iii. Bob sends the message M’ to Alice
iv. The signature along with the message is sent to Alice (M, M’)
v. Bob : M’ = E(M, KpriB)
vi. Signing the message with his private key : S = E(H(M), KpriB) vii. M = E(M’, KpubB)
a. i, iii, ii, v, iv, vii, vi
b. i, ii, iii, iv, v, vi, vii
c. v, vii, ii, i, iii, iv, vi
d. vii, vi, v, iv, iii, ii, i
Answer: b. i, ii, iii, iv, v, vi, vii
These are Blockchain and its Applications Assignment 2 Answers
Q2. Digitally signing transactions by sender in Blockchain does not ensure to solve repudiation/verifiability problems. Is the above statement True or False?
a. True
b. False
Answer: b. False
Q3. Which of the following is used to point a block in blockchain :
a. Hash Pointer
b. User ID
c. Transaction ID
d. Timestamp
Answer: a. Hash Pointer
Q4. Suppose you have 6 data points — 1 to 6. The post-order traversal of the Merkle Tree is given by (here 8 means hash of 8, 43 means the combined hash of 4 and 3, and so on) :
a. {12345656, 1234, 5656, 12, 34, 56, 56, 1, 2, 3, 4, 5, 6}
b. {1, 12, 2, 3, 4, 34, 1234, 5, 6, 56, 123456}
c. {1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 78, 5678, 12345678}
d. {1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 56, 5656, 12345656}
Answer: d. {1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 56, 5656, 12345656}
These are Blockchain and its Applications Assignment 2 Answers
Q5. Which of the following is true for using a digital signature in blockchain?
a. To check the validity of the source of a transactions
b. None of the given options
c. It will ensures that no one can deny of their own transaction
d. It supports user authentication
Answer: a. To check the validity of the source of a transactions
Q6. Which are the main Consensus Algorithms?
a. Proof of Work
b. Proof of Wager
c. Proof of Stake
d. Proof of Mining
Answer: a, b
These are Blockchain and its Applications Assignment 2 Answers
Q7. Why is consensus hard in asynchronous system?
I. No notion of global time
II. faults in network
III. nodes may crash/ faulty nodes
a. II, III
b. I, II
c. I, III
d. I, II, II
Answer: a. II, III
Q8. Liveliness property ensures the output should be produced within a finite time limit?
a. False
b. True
Answer: b. True
These are Blockchain and its Applications Assignment 2 Answers
Q9. Paxos consensus support(s) which of the below properties
a. Liveliness
b. Safety
c. Both
d. None of the above
Answer: c. Both
Q10. Which is/are true for Raft consensus?
a. Crash Fault Tolerant
b. Byzantine Fault Tolerant
c. Both
d. None of the above
Answer: a. Crash Fault Tolerant
These are Blockchain and its Applications Assignment 2 Answers
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These are Blockchain and its Applications Assignment 2 Answers
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