Blockchain is a digital system that stores information across a network in blocks that are linked together. It was introduced in 2008 by an unknown person or group called Satoshi Nakamoto as the technology behind Bitcoin. Since then, it has grown far beyond cryptocurrencies. Today, industries like finance, healthcare, and logistics are using blockchain for secure and transparent operations. As a result, the demand for blockchain developers and architects is rising quickly. If you are preparing for a job in this field, these 40+ commonly asked blockchain interview questions and answers will help you.
Let’s get you fully prepared to nail that interview!
Fun Fact: The blockchain technology market in India is predicted to grow at a rate of 89.4% annually from 2023 to 2030.
Blockchain Interview Overview
| Job Roles | Developer, Engineer, Architect, Analyst |
| Interview Rounds | Aptitude/MCQs, Technical Q&A, Live Coding/Problem-solving |
| Typical Duration | 60 – 90 minutes |
| Question Types | Basics, Smart Contracts, Security, Scaling, Cryptography, Oracles |
| Preparation Time | 2 – 4 weeks (depending on experience level) |
| Top Hiring Companies | TCS, Wipro, Accenture, Google, HCL |
| Salary Range (India) | ₹3 L–₹13 L (Fresher), ₹4 L–₹25 L (Mid), ₹13 L–₹50 L (Architect) |
Blockchain Interview Questions for Freshers
Here are some basic questions on blockchain for freshers and their answers.
- What is blockchain technology?
Blockchain is a digital ledger that records transactions securely and transparently. Each record, called a block, is linked to the previous one, forming a chain. It is decentralized, meaning no single entity controls the system, ensuring security and transparency.
- How does a blockchain work?
Blockchain stores data in blocks, each containing transaction information and a unique hash. These blocks are linked together, forming a chain. Transactions are validated by network participants, called nodes, before being added to the chain. Once added, the data cannot be altered, making the system tamper-proof.
- What are the main components of a blockchain?
The main components include blocks, nodes, and consensus mechanisms. Blocks store data, nodes maintain the blockchain, and consensus mechanisms validate transactions, ensuring all participants agree on the network’s state.
- What is the difference between a public and private blockchain?
A public blockchain is open to anyone, allowing anyone to join, validate, and view transactions. Bitcoin is a public blockchain. A private blockchain is restricted to a set group of participants, providing more control and privacy.
- What is a consensus mechanism in blockchain?
A consensus mechanism is the process by which participants in a blockchain agree on the validity of transactions. Examples include Proof of Work (PoW) and Proof of Stake (PoS), each providing a way to validate transactions securely and efficiently.
Ethereum now uses Proof of Stake (PoS), which consumes less energy and allows staking instead of mining.
- What are some real-world applications of blockchain?
Blockchain is used in cryptocurrencies like Bitcoin, supply chain management, secure voting systems, healthcare data management, and intellectual property protection. It’s also being explored for decentralized finance (DeFi) and identity verification.
Blockchain Technology Interview Questions for Experienced
These are some important interview questions on blockchain technology for experienced candidates.
- How would you improve the scalability of a blockchain network?
“To improve the scalability of a blockchain network, I would use layer 2 solutions like the Lightning Network, which processes transactions off-chain. I’d also consider sharding, increasing the block size, and optimizing consensus algorithms to handle more transactions effectively.”
- Explain the concept of smart contracts.
Smart contracts are self-executing contracts with terms written directly into code. They automatically execute when predefined conditions are met, reducing the need for intermediaries. Ethereum is the most well-known platform for smart contracts.
- What are the most common vulnerabilities in smart contracts?
Common risks include reentrancy attacks, unchecked external calls, and integer overflows. These can be avoided by:
- Using the checks-effects-interactions pattern
- Avoiding call() unless necessary
- Enabling compiler safety checks (Solidity ≥ 0.8)
- Using audit tools like Slither and MythX
- What are network-level threats like 51% attacks, and how are they mitigated?
A 51% attack happens when one group controls over half of the network’s hashing power. They can double-spend or halt confirmations.
Mitigation includes:
- Higher mining costs (makes attack expensive)
- Switching to proof-of-stake (like Ethereum did)
- Using finality gadgets or multiple validator sets
- How do you handle blockchain security concerns?
“To handle blockchain security concerns, I focus on using strong encryption and conducting regular code audits. I also prefer consensus mechanisms like PoS to reduce security risks. For added protection, I opt for private blockchains, as they limit who can join and validate the network.”
- Can you explain how a blockchain handles transactions?
Blockchain transactions are verified by network participants (nodes). Once validated, they are grouped into blocks and added to the chain. Each block links to the previous one via cryptographic hashing, creating an immutable record of all transactions.
- What happens after a transaction is submitted to the blockchain?
Here is what happens –
- Mempool: The transaction waits in a temporary pool with others.
- Gas Fees: Users attach gas to prioritize their transaction.
- Validation: A miner or validator picks it up, checks the signature and balance.
- Block Addition: If valid, it’s added to a block.
- Confirmation: Once the block is mined/validated and added to the chain, the transaction is confirmed.
The higher the gas, the faster the inclusion. Congestion can slow this process.
After confirmation, finality is reached when the network agrees the transaction can’t be reversed.
- What are some key challenges in implementing blockchain technology?
Challenges include scalability, high energy consumption (especially with PoW), and regulatory uncertainty. Integration with existing systems can also be complex and costly, requiring collaboration among various stakeholders.
Blockchain Developer Interview Questions
Let’s take a look at some blockchain interview questions and answers for a blockchain developer.
- How would you build a decentralized application (dApp) on the blockchain?
“To build a dApp, I would start by choosing a blockchain like Ethereum. I’d write the smart contracts using Solidity and use Web3.js to interact with those contracts. For storing larger data that doesn’t fit on the blockchain, I’d use decentralized storage solutions like IPFS. For the front end, I’d use React with Web3.js or Ethers.js to connect to the blockchain.”
- What programming languages are used in blockchain development?
Common languages include Solidity for Ethereum smart contracts, Python, JavaScript, Go, and Rust. Each platform may have specific languages, but Solidity is the most widely used for developing smart contracts.
- Can you explain the difference between Ethereum and Bitcoin in terms of blockchain development?
Bitcoin’s blockchain focuses on peer-to-peer transactions and uses PoW for consensus. Ethereum supports dApp development and smart contracts, offering more flexibility and a broader ecosystem for developers. Ethereum also uses a more versatile approach to consensus.
Also Read - Top 10 Most Popular Programming Languages of the Future
Advanced Cryptography Interview Questions
These questions are often asked in senior blockchain roles where cryptography is key. Keep your answers clear and practical.
- What are trapdoor functions? How are they used in blockchain?
A trapdoor function is easy to solve in one direction but hard to reverse unless you know a special secret (the “trapdoor”). Blockchain uses them in public-key cryptography – for example, to generate wallet addresses and verify digital signatures.
- Compare SHA-256, SHA-3, and RIPEMD-160.
- SHA-256: Used in Bitcoin. Part of the SHA-2 family. Strong and widely trusted.
- SHA-3: Based on a different algorithm (Keccak). Not an upgrade of SHA-2 but a separate option.
- RIPEMD-160: Produces shorter hashes. Used with SHA-256 in Bitcoin addresses (to shorten output).
- What are zk-SNARKs and how do they enable privacy?
zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge) allow users to prove something is true without revealing the actual data. In blockchains like Zcash, they are used to hide transaction details while still proving validity.
- How does hashing ensure immutability in blockchain?
Each block contains a hash of the previous block. If someone tries to change past data, all future hashes break. This chain of hashes makes the blockchain tamper-proof.
Blockchain Engineer Interview Questions
Here are some important blockchain interview questions for blockchain engineer.
- What are the key differences between Proof of Work and Proof of Stake?
PoW requires miners to solve computational puzzles to validate transactions, which is energy-intensive. PoS relies on validators who lock up cryptocurrency to validate transactions, making it more energy-efficient and faster.
- How do you optimize the performance of a blockchain network?
“To optimize the performance of a blockchain network, I focus on implementing layer 2 solutions and increasing block size where possible. I also use more efficient consensus mechanisms and apply sharding to split the blockchain into smaller, manageable parts.”
- What are the security risks in blockchain networks and how do you mitigate them?
Security risks include 51% attacks, wallet hacks, and smart contract vulnerabilities. These can be mitigated through robust encryption, multi-signature wallets, regular audits, and using secure coding practices in smart contracts.
- What is a reentrancy attack in smart contracts? How do you prevent it?
It happens when an external contract is called before the original contract updates its state. The external contract can re-enter and call the function again, draining funds.
How to prevent it:
Use the checks-effects-interactions pattern and update state before making external calls. Also, avoid using call() without a reentrancy guard.
- How do fallback functions create vulnerabilities in Solidity?
Fallback functions run when no other function matches. If they include logic like sending Ether or modifying state, attackers can exploit them – especially if the contract receives unexpected input.
Prevention:
Keep fallback functions empty or restricted, and validate msg.data properly.
- What is integer overflow/underflow and how is it mitigated in blockchain apps?
When a number exceeds its max or drops below zero, it “wraps around” to a wrong value — causing logic errors.
Mitigation:
Use Solidity version ≥ 0.8.0 (which has built-in checks), or libraries like SafeMath in earlier versions.
Blockchain Scaling & Performance Interview Questions
As blockchains grow, they often struggle with speed and high fees. These questions focus on how different technologies solve those problems.
- What is sharding in blockchain, and how does it improve performance?
Sharding splits the blockchain into smaller parts called “shards.” Each shard processes its own set of transactions, which increases overall throughput and reduces congestion. Ethereum plans to use sharding in future updates.
- Explain Layer 2 solutions like Optimistic Rollups and ZK-Rollups.
Layer 2 sits on top of the main blockchain.
- Optimistic Rollups assume transactions are valid by default and only check them if someone disputes.
- ZK-Rollups use cryptographic proofs to verify batches of transactions instantly.
Both help reduce gas fees and speed up processing.
- How do sidechains help scale blockchain networks?
A sidechain is a separate blockchain connected to the main chain. It handles some of the workload and then communicates results back. This allows more transactions without overloading the main network.
- What is a DAG and how is it different from traditional blockchains?
DAG (Directed Acyclic Graph) stores data in a graph instead of blocks in a chain. It allows multiple transactions to be confirmed at the same time. Platforms like IOTA and Hedera use DAGs for faster, feeless transactions.
Interview tip – If asked to choose between scaling methods, compare them on speed, security, and decentralization trade-offs.
Hyperledger Fabric Interview Questions
These are some blockchain interview questions on Hyperledger fabric.
- What is Hyperledger Fabric and how does it differ from other blockchain platforms?
Hyperledger Fabric is a permissioned blockchain platform designed for enterprise use. Unlike public blockchains, it provides more control, privacy, and customizability, allowing businesses to set up private networks with different consensus mechanisms.
- Can you explain the role of endorsing peers in Hyperledger Fabric?
Endorsing peers validate transactions before they’re added to the blockchain. They ensure the transaction complies with the smart contract (chaincode) logic and provide an endorsement that is required for the transaction to be accepted by the network.
- What is the process of setting up a Hyperledger Fabric network?
Setting up a Hyperledger Fabric network involves defining organizations, channels, and peers. A Certificate Authority (CA) is used to manage identities, and smart contracts are deployed to handle transaction logic. The network must also configure consensus mechanisms and validate transactions.
Blockchain Architect Interview Questions
- What are the design principles of blockchain architecture?
Blockchain architecture should be secure, scalable, decentralized, and transparent. It should be modular for easy upgrades and support interoperability with existing systems. Privacy and consensus mechanisms are also critical elements in architecture design.
- How do you choose the right blockchain platform for an enterprise solution?
“When choosing the right blockchain platform for an enterprise solution, I consider factors like scalability, privacy, security, transaction speed, and ecosystem support. For private, permissioned blockchains, I’d go with Hyperledger Fabric. For public decentralized applications, Ethereum is usually my top choice.”
Interview Questions on Oracles and Off-Chain Data in Blockchain
Smart contracts can’t access real-world data on their own. That is where oracles come in. These questions test your understanding of how external data is brought into blockchain apps.
- What are blockchain oracles?
Oracles are services that send outside data into a blockchain. For example, a smart contract may need live weather info, match results, or asset prices – and an oracle fetches that data.
Without oracles, smart contracts can only work with on-chain information.
- What is an oracle manipulation attack? How can it be prevented?
This happens when an attacker feeds false data into the smart contract by exploiting a weak or centralized oracle. If the contract depends on price feeds, this can be used to drain funds or cheat the logic.
Prevention:
- Use decentralized oracles like Chainlink.
- Add time delays and data validation steps.
- Avoid single points of failure.
Tip – If asked in interviews, mention real examples like Chainlink, Band Protocol, or Uniswap’s TWAP for price data.
IBM Blockchain Interview Questions
Here are some important IBM blockchain interview questions and their answers.
- What is IBM Blockchain and how does it work?
IBM Blockchain is a platform built on Hyperledger Fabric. It enables businesses to create secure, transparent blockchain networks. IBM provides tools for developing, managing, and scaling blockchain networks in an enterprise environment.
- Can you explain IBM’s approach to integrating blockchain with enterprise systems?
IBM’s approach involves creating private blockchain networks tailored to business needs. The platform integrates with existing enterprise systems like supply chain management, payment systems, and databases, offering a seamless and secure way to track data and transactions.
Blockchain Wallets and Key Management Interview Questions
Managing crypto assets safely is a big part of working with blockchain. These interview questions test your understanding of how wallets and keys work behind the scenes.
- Explain hot wallet vs cold wallet.
| Feature | Hot Wallet | Cold Wallet |
| Connection | Always connected to the internet | Fully offline |
| Security | More exposed to hacks | Safer from online attacks |
| Use case | Quick access and frequent transactions | Long-term storage of large amounts |
| Examples | Mobile apps, browser extensions | Hardware wallets, paper wallets |
- How do public-private key pairs work?
In blockchain, every wallet is based on a key pair:
- The private key is secret – it lets you sign transactions and move funds.
- The public key is visible to others – it is used to receive funds.
A message signed with a private key can be verified using the matching public key. That is how blockchains confirm ownership.
- What is a keystore file?
A keystore file is an encrypted version of your private key. It is stored as a JSON file and protected by a password. Many wallets (like MetaMask or MyEtherWallet) use keystore files to import or recover accounts.
Tip – In interviews, be ready to explain what happens if someone loses their private key or password – and why seed phrases matter.
Blockchain Technology Viva Questions
- What is the significance of decentralization in blockchain?
Decentralization makes the network more secure and transparent. It removes single points of control, reducing the risk of fraud and censorship. All participants have an equal say, increasing trust in the system.
- How do hash functions work in a blockchain?
Hash functions take input data and generate a unique output, called a hash. In blockchain, each block contains a hash of the previous block, linking them together securely and preventing tampering.
- Explain the concept of a blockchain ledger.
A blockchain ledger is a shared, immutable record of transactions. All participants have access to the ledger, which updates automatically with new transactions, ensuring transparency and security.
- Can you explain the concept of a fork in a blockchain network?
A fork happens when there’s a change in blockchain protocol, creating two diverging versions. A hard fork creates a completely new blockchain, while a soft fork is compatible with the old version.
Enterprise Use Cases of Blockchain
Blockchain is not just for crypto. Big companies now use it to solve everyday business problems. Here are a few real examples that often come up in interviews –
- Supply Chain Tracking (IBM + Maersk)
Shipping data is recorded on blockchain to avoid delays, reduce fraud, and keep all parties updated in real time.
- Digital Identity (India’s Aadhaar pilot)
Blockchain helps store identity data securely. It gives people more control and makes KYC checks faster.
- Cross-Border Payments (Ripple)
Banks use blockchain to send money abroad in seconds, without relying on old systems like SWIFT.
- Healthcare Records (Estonia)
Medical data is stored on blockchain. Doctors can access the right information, and patients stay in control.
- Real Estate Tokenization (RealT)
Property ownership is split into tokens. People can invest small amounts and trade them easily.
- Trade Finance (HSBC + ING)
Letters of credit and trade documents are moved to blockchain, cutting processing time from days to hours.
Interview tip – If asked about use cases, don’t just name them. Explain how blockchain makes the process simpler, faster, or safer.
Tips to Crack Blockchain Interview
Use these simple strategies to succeed in your interview – even if you are just starting out in blockchain.
- Show you understand the why behind blockchain. Don’t just define terms. Explain why decentralization matters or why gas fees exist.
- Talk about your own projects – no matter how small. Even a basic smart contract on Remix shows initiative. Add it to your resume or GitHub.
- Ask smart questions about the tech stack. For example: “Are you using EVM-compatible chains or something like Solana for performance?”
- Bring up Layer 2 or oracles if the role involves DeFi. Asking about Chainlink or Optimistic Rollups shows you understand real-world blockchain problems.
- Mention security if the role involves smart contracts. Say you are aware of issues like reentrancy, overflow, or access control. Audits matter.
- Keep up with recent changes – and mention them. Know what is happening with Ethereum 2.0, account abstraction, or changes in gas pricing.
- If you don’t know something, admit it. It’s okay to say, “I haven’t worked with that yet, but I am learning it now.”
Wrapping Up
Preparing for Blockchain interview questions is crucial for landing a role in this rapidly growing field. Whether you are a fresher or an experienced professional, having a solid understanding of blockchain concepts is key to success. If you are looking for the best IT jobs in India, including blockchain job roles, check out Hirist. It is a top online job portal where you can find great opportunities to advance your career.
FAQs
According to AmbitionBox, the average annual salary for a blockchain developer in India is ₹9.8 Lakhs, with a typical range between ₹2 Lakhs to ₹20 Lakhs.
Yes, for most roles. Solidity, JavaScript, and Python are commonly used in blockchain development.
You should know blockchain basics, cryptography, smart contracts (Solidity), and one programming language like JavaScript or Python. Understanding security and gas optimization also helps.
Yes. With rising demand across industries like finance, logistics, and healthcare, blockchain roles offer strong growth, high salaries, and future-ready skills.
TCS, Wipro, Accenture, Tech Mahindra, Infosys, and startups like SoluLab and Auxesis Labs are active recruiters.
