NPTEL Blockchain and its Applications Week 1 Assignment Answers 2025
1. Which of the following statements is true regarding the foundational concepts of blockchain and cryptography?
a) Decentralization in blockchain ensures that a single authority controls the network for higher
efficiency.
b) SHA-256 is a cryptographic hash function widely used in blockchain due to its fixed output size and collision resistance.
c) A hash chain is a sequence of cryptographic keys used to decode blockchain data.
d) Cryptographic hash ensures that the blockchain data cannot be read by anyone outside the
network.
Answer :- b
2. An attacker wants to find a collision in a cryptographic hash function with a 256-bit output. What is the approximate number of hash operations required to succeed?
a) 1 × 2128
b) 0.75 × 2128
с) 1 × 2256
d) 0.5 × 2256
Answer :- a
3. A blockchain network uses SHA-256 for its hashing process. If it takes 10-6 seconds to compute a single SHA-256 hash, how long would it take (approximately) to compute 2128 hashes for a collision attack?
a) 1010 years
b) 1015 years
c) 1020 years
d) 1025 years
Answer :- d
📚 Did you know that 60-80% of the questions in the final exam are often repeated from previous years? 🎯 Boost your chances of success by exploring answers for NPTEL courses from past years on Answer GPT! 👇👇👇👇
![[Week 1-12] NPTEL Blockchain and its Applications Assignment Answers 2025](https://answergpt.in/wp-content/uploads/2025/01/Blockchain-and-its-Applications-2025.jpg)
![[Week 1-12] NPTEL Blockchain and its Applications Assignment Answers 2024](https://answergpt.in/wp-content/uploads/2024/01/NPTEL-Blockchain-and-its-Applications-Assignment-Answers-2024.jpg)
4. In a decentralized distributed system with 100 participants, which of the following statements is true regarding trust and communication?
a) At least 50 participants must trust each other for the system to function.
b) A central body governing communication among all 100 participants is mandatory.
c) Participants may or may not trust each other, as the system ensures integrity using
cryptographic protocols and agreement through consensus protocols.
d) All the 100 participants must trust each other.
Answer :- For Answer Click Here
5. A blockchain network achieves an average block generation time of 5 minutes under normal
conditions. However, due to scheduled maintenance, the network’s hash rate is reduced by 50% for 4 hours daily. If the network operates for 12 hours in total (including the maintenance period), how many blocks will be added to the blockchain?
a) 120
b) 200
c) 216
d) 240
Answer :-
6. Where are the transaction logs stored in a blockchain network?
a) In a centralized SQL database.
b) On an immutable ledger controlled by a central authority.
c) In metadata tables on each peer.
d) In the distributed ledger of each peer across the network.
Answer :- For Answer Click Here
7. Which of the following describes the avalanche effect in a cryptographic hash function?
a) Given the same input, the hash function returns a different hash 99.99% of the time.
b) It takes 105 attempts to reverse-engineer the original message from the hash.
a) A small change in the input causes a drastic change in the hash, flipping nearly all the bits.
c) The hash function always returns the same hash for the same input.
Answer :-
8. Which of the following statements accurately describes a blockchain?
a) A centralized database where data is stored on a single server.
b) distributed ledger where data is stored across multiple nodes and is immutable.
c) system that only stores cryptocurrency transaction data on a single node.
d) A network that uses a single user to control access and updates to the data.
Answer :-
9. Which of the following is/are possible use cases of blockchain technology?
a) Cross-border payments
b) Supply chain management
c) Centralized Anti-money laundering tracking system
d) Maintaining data over a single database server
Answer :-
10. In a blockchain using SHA-256, if the hashes of strings A and B are concatenated and then hashed again, what is the length of the final hash?
a) 256 bits
b) 512 bits
c) 128 bits
d) 1024 bits
Answer :- For Answer Click Here
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
Answer :- b
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 :- c
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 :- b
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 :- For Answers Click Here
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
Answer :- For Answers Click Here
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
Answer :- For Answers Click Here