Blockchain and its Applications Week 1 NPTEL Assignment Answers 2025

NPTEL Blockchain and its Applications Week 1 Assignment Answers 2024

Q1. What are the features of a hash function?

a. Puzzle-friendly
b. Collision-resistance
c. Deterministic
d. Post image resistance

Answer: a, b, c
Explanation:

• Puzzle-friendly: The hash must be hard to reverse-engineer; useful in mining (Proof of Work).
• Collision-resistance: It should be extremely unlikely that two different inputs produce the same hash.
• Deterministic: The same input always results in the same hash output.
• Post image resistance is not a standard term in cryptographic hash functions.

---

Q4. Which of the statements below is/are true for decentralized distributed systems?

a. Players may or may not trust each other
b. Players must trust each other
c. Central body should govern the communication
d. None of the above

Answer: a
Explanation:
In decentralized systems like blockchain, trust is minimized between participants. They may not trust each other, but consensus protocols maintain system integrity.

---

Q5. Miner nodes only execute new transactions but cannot verify previous transaction hash?

a. True
b. False

Answer: b
Explanation:
False – Miner nodes not only execute new transactions but also verify the validity of previous transaction hashes to ensure integrity.

---

Q6. Which of the following is/are true for blockchains?

a. Works based on Push technique
b. Existing data can be deleted easily
c. Tamper-proof
d. None of the above

Answer: a, c
Explanation:

• Push technique: Data is broadcasted across the network (push, not pull).
• Tamper-proof: Due to cryptographic linking, altering data is computationally expensive.
• Data can’t be deleted easily, making option b incorrect.

---

Q7. Where are the ledger logs stored in a blockchain?

a. On a SQL Database
b. On a central immutable ledger
c. On a metadata table
d. In ledger of each peer

Answer: d
Explanation:
Each node (peer) maintains a copy of the ledger, making the blockchain decentralized and fault-tolerant.

---

Q8. Which of the following is an avalanche effect to a cryptographic hash function?

a. Given the same message the hash function would not return the same hash
b. It is not very difficult to generate the original message from the hash
c. A small change in the message impacts large change in the hash value
d. None of the above

Answer: c
Explanation:
The avalanche effect ensures that a tiny change in input causes major changes in output hash, which improves security.

---

Q9. Genesis blocks may not contain the

a. First transaction
b. First transaction block
c. Last transaction block
d. None of the above

Answer: c
Explanation:
The genesis block is the first block in a blockchain. It can’t contain the last transaction block.

---

Q10. Which of the below is/are blockchain-based app examples?

a. Cross-border payments
b. Supply chain
c. Anti-money laundering tracking system
d. UTXO

Answer: a, b, c
Explanation:

• Blockchain is widely used in cross-border payments, supply chain tracking, and AML systems for transparency.
• UTXO (Unspent Transaction Output) is a mechanism, not an application.