(SEM VI) THEORY EXAMINATION 2022-23 BLOCKCHAIN ARCHITECTURE DESIGN

BLOCKCHAIN ARCHITECTURE DESIGN – KIT-061

Section-wise Important Questions & Ready Answers

SECTION A

(Attempt all questions – 2 marks each)

(a) Formal Definition of Blockchain

Blockchain is a distributed, decentralized, and immutable digital ledger that records transactions in blocks. Each block is cryptographically linked to the previous block, ensuring data integrity, transparency, and security without relying on a central authority.

(b) Types of Blockchain

Blockchains are broadly classified into Public blockchain, Private blockchain, Consortium blockchain, and Hybrid blockchain. Public blockchains are open to everyone, private blockchains are controlled by a single organization, consortium blockchains are managed by a group of organizations, and hybrid blockchains combine features of public and private systems.

(c) Effect of Modifying a Block by an Adversary

If an adversary changes the transaction of a block, the block’s hash changes. This breaks the cryptographic link with the next block, making the entire chain invalid unless the attacker recalculates all subsequent hashes, which is computationally infeasible in a secure blockchain.

(d) Mining in Public Blockchain

Mining is the process of validating transactions and adding new blocks to the blockchain. Miners solve complex cryptographic puzzles using computational power. The first miner to solve the puzzle adds the block and receives a reward.

(e) Channels in Hyperledger Fabric

Channels in Hyperledger Fabric are private communication paths that allow a subset of network participants to share data securely and confidentially without exposing it to the entire network.

(f) Properties of Smart Contracts

Smart contracts are autonomous, deterministic, tamper-proof, transparent, and self-executing programs that run on the blockchain and enforce agreements automatically when predefined conditions are met.

(g) Pros and Cons of Blockchain in Trade/Supply Chain

Blockchain improves transparency, traceability, trust, and fraud reduction in supply chains. However, challenges include scalability issues, integration complexity, regulatory uncertainty, and high initial implementation cost.

(h) PBFT Byzantine Nodes Calculation

In PBFT, the condition is:

n≥3f+1n \ge 3f + 1n≥3f+1

If Byzantine (faulty) nodes f=5f = 5f=5:
Total nodes n=3(5)+1=16n = 3(5) + 1 = 16n=3(5)+1=16
Honest nodes = 16 − 5 = 11

(i) Private and Public Key Cryptography

Public key cryptography uses a pair of keys: a public key for encryption and a private key for decryption. Private key cryptography uses a single shared secret key for both encryption and decryption.

(j) Security Mechanism in Blockchain

Blockchain security relies on cryptographic hashing, digital signatures, consensus algorithms, decentralization, and immutability to protect data from tampering and unauthorized access.

SECTION B

(Attempt any three – 10 marks each)

2(a) Centralized, Decentralized, and Distributed Architectures

In centralized architecture, a single authority controls data and operations. Decentralized architecture distributes control among multiple nodes, reducing single-point failure. Distributed architecture spreads computation and data across multiple independent nodes. Decentralized and distributed systems offer better fault tolerance and security than centralized systems.

2(b) Consensus Algorithm and Requirements

A consensus algorithm enables nodes in a blockchain network to agree on a single valid state. Key requirements include agreement, termination, fault tolerance, validity, and resistance to malicious behavior.

2(c) Hyperledger Fabric and Consensus Decomposition

Hyperledger Fabric is a permissioned blockchain framework. Its consensus process is decomposed into three phases: transaction execution, ordering, and validation, improving scalability and modularity.

2(d) Public Distribution System (PDS) and Blockchain

Traditional PDS suffers from corruption and lack of transparency. Blockchain-based PDS ensures traceability, immutability, and transparent distribution of resources, reducing fraud compared to centralized systems.

2(e) Elliptic Curve Cryptography Numerical

Given elliptic curve E11(1,6)E_{11}(1,6)E11​(1,6) and point P(2,7)P(2,7)P(2,7), doubling the point involves slope calculation and modular arithmetic. The result of 2P2P2P is obtained using elliptic curve point-doubling formulas.

SECTION C

3(a) Merkle Trees and Their Use in Blockchain

A Merkle tree is a binary tree of hashes where each leaf node represents transaction data and parent nodes store hashes of their children. It enables efficient verification, reduces storage, and ensures data integrity in blockchain systems.

3(b) Merkle Tree Construction and Traversals

Given eight transactions ordered from 8 to 1, hashes are paired iteratively until a single root hash is formed.

In-order traversal visits left subtree, root, right subtree

Pre-order traversal visits root, left, right

Post-order traversal visits left, right, root