Blockchain Interview Questions

Blockchain is a decentralized, distributed digital ledger that records transactions across many computers in a way that ensures the data cannot be altered retroactively without altering all subsequent blocks.

Transactions are grouped into blocks. Each block contains a hash of the previous block, a timestamp, and transaction data. Blocks are linked in a chain using cryptographic principles, ensuring integrity and immutability.

• Decentralization
• Transparency
• Immutability
• Security
• Consensus mechanisms

A block is a data structure that stores transaction records and metadata, such as a timestamp, nonce, and hash of the previous block.

A smart contract is a self-executing contract with the terms written directly into code. It runs on the blockchain and automatically enforces rules and conditions without needing intermediaries.

A consensus algorithm ensures all nodes in a blockchain network agree on the same version of the ledger. Examples include Proof of Work (PoW), Proof of Stake (PoS), and Delegated Proof of Stake (DPoS).

• Public: Open to everyone (e.g., Bitcoin, Ethereum).
• Private: Access is restricted to specific participants (e.g., Hyperledger).

Cryptography secures transactions, ensures user anonymity, and protects data integrity using techniques like hashing and digital signatures.

A hash function takes input data and returns a fixed-size string (hash). It's one-way and collision-resistant, ensuring security and integrity in the blockchain.

PoW is a consensus algorithm where participants (miners) solve complex mathematical problems to validate transactions and create new blocks, used in Bitcoin.

PoS selects validators based on the number of coins they hold and are willing to "stake" as collateral. It’s energy-efficient compared to PoW.

Mining is the process of validating transactions and adding them to the blockchain by solving cryptographic puzzles. Miners are rewarded with cryptocurrency.

Nodes are computers that participate in the blockchain network. They store, validate, and share the blockchain ledger.

A fork is a divergence in the blockchain protocol:

• Soft Fork: Backward-compatible change.
• Hard Fork: Non-backward-compatible change, creating a new chain.

A digital signature uses public-key cryptography to verify the authenticity and integrity of a message, transaction, or data.

Ethereum is a decentralized blockchain platform that allows developers to build and deploy smart contracts and decentralized applications (dApps).

• Bitcoin: Primarily a digital currency.
• Ethereum: A platform for smart contracts and dApps with its own cryptocurrency, Ether (ETH).

Gas fees are the costs paid to miners for performing transactions or executing smart contracts on the Ethereum network.

Hyperledger is an open-source collaborative project by the Linux Foundation aimed at developing enterprise-grade blockchain solutions (e.g., Hyperledger Fabric).

• Cryptocurrencies (Bitcoin, Ethereum)
• Supply chain management
• Healthcare data sharing
• Digital identity
• Voting systems
• Financial services