NPTEL Blockchain and its Applications Week 2 Assignment Answers 2025
1. Alice employs the RSA cryptosystem with the prime numbers p=11 and q=19 to derive her public and private keys. Given that her public key is e=11, what is her corresponding private key d?
a) 35
131
c) 101
d) 149
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2. Alice wants to send a message to Bob with confidentiality and integrity. The steps are as follows:
1. Alice encrypts the message using Bob’s _____________key.
2. Alice then signs the _____________-of the message with her _____________key.
3. Bob decrypts the message using his ____________key.
4. Bob verifies Alice’s signature using her __________key.
a) public, hash, private, public, private
b) private, message, public, private, public
c) public, hash, private, private, public
d) public, hash, private, public, public key.
Answer :-
3. Digitally signing transactions by the sender in Blockchain ensures the resolution of repudiation/verifiability problems. Based on this, which one of the following is correct:
a) It allows the sender to deny the transaction at any point.
b) It ensures that the sender cannot deny the transaction and the recipient can verify its authenticity.
c) It provides encryption but does not verify the sender’s identity.
d) It guarantees the transaction will remain confidential but does not resolve repudiation issues.
Answer :-
4. What is the primary purpose of Alice signing a message with her private key in a blockchain
transaction?
a) To encrypt the message
b) To prevent others from reading the message
c) To prove the message came from Alice
d) To hide the contents of the message
Answer :-
5. Consider 6 data points labeled 1 to 6. The post-order traversal of the Merkle Tree is provided as
follows (where 1 represents the hash of data point 1, 43 denotes the combined hash of 4 and 3, and so on):
a) (12345656, 1234, 12, 1, 2, 34, 3, 4, 5656, 56, 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, 56, 5656, 12345656}
d) {1, 2, 12, 3, 4, 34, 1234, 5, 6, 56, 5656, 12345656}
Answer :-
6. Which of the following is used to refer to a block in a blockchain?
a) Future nonce
b) Block size
c) Previous Block Hash
d) Transaction Timestamp
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7. Which of the following does not align with the primary design goals of cryptocurrency development?
a) Decentralization of control and decision-making
b) Immutability of transaction records
c) Centralized control over transactions
d) Transparency and accessibility of transaction data
Answer :-
8. Which of the following statements is/are true regarding Bitcoin and its consensus algorithm?
1. Miners are rewarded with transaction fees and block rewards in Bitcoin.
2. Bitcoin uses Proof of Work (PoW) for transaction validation and block addition.
3. Bitcoin operates on a peer-to-peer (P2P) network.
4. Bitcoin uses Proof of Stake (PoS) for centralization.
a) 1, 2, 3
b) 2,3,4
c) 1, 2.4
d) 1,3,4
Answer :-
9. What is the primary focus of ‘safety’ in Bitcoin’s protocol?
a) Preventing invalid transactions
b) Ensuring blocks are mined quickly
c) Guaranteeing that only some of the transactions are private
d) Maximizing the number of transactions per block
Answer :-
10. Which of the following is the primary goal of a consensus algorithm in a distributed system?
a) To ensure that all nodes process transactions at the same speed
b) To guarantee that all nodes in the system agree on a single value or state
c) To minimize the number of nodes required for network communication
d) To prevent malicious attacks by encrypting all data transmitted between nodes
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