21 Most Popular Blockchain Developer Interview Questions

Disruptive technologies like blockchain, artificial intelligence, the internet of things, and virtual reality have had a profound impact on the way humans live their lives and are today being adopted widely across industries. India has not been left out by the wave of emerging technologies that have revolutionized the globe in the past decade. With a vibrant IT industry and growing opportunities in the cryptocurrency field, the cities to look out for are Mumbai, Bengaluru, and Gurgaon which together account for up to 60% of blockchain-related job openings. Blockchain training in Mumbai has picked up fast as more IT professionals consider upskilling to acquire blockchain skills. 

A blockchain professional is one who possesses an in-depth understanding of blockchain concepts and principles and can implement blockchain solutions successfully in business based on the business requirements. These individuals have vast knowledge and experience dealing with various blockchain-powered platforms and security systems; can develop database structures, distributed ledger systems, and smart contracts; and typically have a strong background in programming. 

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With the demand for blockchain developers and engineers on the rise, professionals ought to prepare adequately for interviews. Here are the most popular blockchain developer questions you can expect to be asked in an interview. 

  1. How do you determine the blockchain requirements of a business and implement a blockchain solution?  

This is a project management and blockchain-oriented question that tests a candidate’s ability to not only develop to implement blockchain solutions but also collaborate with others in doing so. The steps involved in blockchain solution implementation are: 

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  • Requirements gathering and building a use-case
  • Develop a proof of concept (POC)
  • Select a blockchain platform for the solution 
  • Build and test the blockchain solution
  • Manage the network in production 
  • Deploy the blockchain solution 
  • Select the appropriate consensus protocol 
  • Develop blockchain ecosystem for the solution 
  1. Are there any special requirements for integrating blockchain technology in the business? 

While there are no specific requirements for implementing blockchain solutions, it is important to bear in mind that blockchain technology should be deployed on a peer-to-peer network. Others include data interoperability, smart contract functionality, and security. 

  1. What is the principle underlying blockchain technology?  

The core principle underpinning blockchain technology is distributed ledger where each participant in the blockchain infrastructure has equal access to the entire ledger and no single entity controls it making the records incorruptible.  

  1. What are the key features of blockchain technology? 

The core features of blockchain are 

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  • A decentralized system 
  • A distributed database
  • Transparency with pseudonymity 
  • Immutability of records 
  • Computational logic 
  1. What are the core components of blockchain?  

Blockchain is comprised of three core components which are: 

  • Block. A record of transactions entered into a ledger over a specified time period. 
  • Chain. Blocks in a blockchain network are joined together by a hash to form a chain of blocks. 
  • Node application. An internet-connected computer that participates in the blockchain ecosystem that stores the updated blockchain version. 
  • Peer-to-peer network. All the nodes in the blockchain ecosystem are interconnected and work together in a shared ledger of transactions where each node in the network stores an encrypted copy of the transactions. 
  • Consensus algorithm. A process through which a single state of the blockchain is agreed upon by all the nodes in a blockchain peer-to-peer network to achieve security and immutability of records in the blockchain. 
  1. How is a block identified in the blockchain network?  

A block is identified by a cryptographic hash generated by the SHA-256 algorithm on the block header. The hash is created with reference to the block created before it. 

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  1. What is SHA-256 in blockchain?  

SHA-256 (Secure hash algorithm 2) is a cryptographic hash function with a 256-bit digest length. Hashing in encryption is the process by which data is transformed into a format that can only be read by its specific key. The SHA-256 hash function transforms information into blocks of  256-bit (32 bytes) string size. It is a keyless function that makes it one of the most secure hash functions used in popular encryption and authentication protocols like SSL, SSH, PGP, and others to secure passwords. Cryptocurrencies like Bitcoin use the SHA-256 hash function to validate transactions.  

  1. List some of the most popular consensus algorithms 

Some popular consensus algorithms are: 

  • Proof-of-work (PoW)
  • Proof-of-stake (PoS)
  • Delegated proof-of-stake (DPoS)
  • Proof-of-elapsed-time (PoET)
  • Proof-of-importance  (PoI)
  • PBFT (Practical Byzantine Fault Tolerance) 
  • RPCA (Ripple Protocol Consensus Algorithm) 
  1. What is the difference between Proof-of-Stake and Proof-of-Work?

Proof-of-stake and Proof-of-work are two of the most popular consensus algorithms used to validate cryptocurrency transactions.  

  • Proof-of-stake is the concept in which miners are randomly selected to validate transactions and mine blocks. However, miners who own the highest number of tokens have higher stakes in the network. This algorithm is considered less costly and requires less computational resources.  
  • Proof-of-work, on the other hand, is based on direct competition between miners where they compete to solve complex cryptographic puzzles to validate transactions on the network and get rewarded with new blocks. This consensus requires much computational power to solve cryptographic puzzles which turns out to be costly and environmentally unfriendly. 
  1. Explain mining in blockchain 

Mining is the process by which transactions in the blockchain network are validated by solving complex mathematical equations. Mining results in the creation of new cryptocurrency in the network and proof-of-work for the validated transaction.

  1. Explain encryption and its importance in blockchain 

Encryption is the process of transforming plain text into a format that is unreadable by humans or computers unless they have the private key to decrypt it back to plain text. In the blockchain, encryption is used as an approach to securing block records from being accessed by unauthorized parties. 

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  1. Name two types of records stored in the blockchain database

Two types of records stored in the blockchain database are: 

  • Transaction records 
  • Block records 
  1. Why are coins and tokens important in Blockchain? 

Coins are essentially digital money and are often used as a medium of exchange. Tokens on the other hand refer to digital assets. Transactions in blockchain are evidenced by a change of state where coins move from one address to another. For instance, coins can move from one address to another during the purchase of tokens. Coins and tokens can also be used as incentives for people to join a blockchain network. 

  1. What are Merkle Trees and why are they important? 

Also referred to as a hash tree, a Merkle tree is a data structure containing cryptographic hashes of all the blocks in a blockchain. The leaf nodes are labeled with the hashes of the data blocks while the non-leaf nodes represent the hashes of the child nodes. 

Merkle trees provide a way of downloading a lighter version of the chain of block headers consisting of only hashes rather than downloading all the transactions in the blockchain which requires considerably large memory. 

  1. What are off-chain transactions? 

Off-chain transactions are transactions that move the value of transactions outside the blockchain. These transactions are validated and recorded using other techniques. 

  1. Name some of the core principles in blockchain that are implemented to eliminate security threats. 

Some principles used to eliminate security threats in blockchain are:  

Data protection Application protection Infrastructure protection 
Cryptography Digital workforce training Vulnerability scanning 
Decentralization Auditing Virtual private network (VPN) getaways 
Data minimization Secure application development Non-Interactive Zero-Knowledge Proof System
Distributed network 
Pseudonymized Network
  1. Explain 51% attack? 

A 51% attack is a scenario in which a group of miners holding more than 50% of the mining hash rate or computing power can collude to manipulate new transactions in the blockchain which could result in the theft of digital assets, altering of transactions, or double-spending. While this situation is highly unlikely, it is possible. 

  1. What is double-spending and how can it be prevented?  

When double-spending occurs when one digital token is spent more than once. Digital currency, unlike traditional currency, is susceptible to being reproduced. 

Decentralization in blockchain overcomes double spending, as participating nodes in a network have to validate a transaction using consensus mechanisms or proof-of-work before the transaction can be recorded on the blockchain ledger. 

  1. What is secret sharing in blockchain?  

Secret sharing refers to a blockchain concept in which information is split among participating nodes in a network with the recipient marked as the destination of the data. Each participant has access to only a part of the information. The receiver receives parts of the data from each participant and combines it to get the information. This is one approach to enhancing security in blockchain. 

  1. What is the importance of blind signature in blockchain? 

This is a type of digital signature whereby the message is blinded before it is signed. This approach is usually implemented in protocols where the author of the message and the signer are different parties thus the signer does not have access to the message content. 

  1. What are the benefits of blockchain to an organization?  
  • Blockchain is secure as it has no single point of failure 
  • Traceability of records 
  • Immutability of records 
  • Cost-effective as it eliminates intermediaries 
  • Transparency of transactions as anyone can access 


Blockchain technology has matured fast and is being adopted widely especially in the supply chain, healthcare, as well as banking, and financial services industries. The demand for blockchain professionals is nearly unquenchable. However, recruiters still value demonstrated knowledge and practical experience. Consider enrolling in a blockchain certification course to build your knowledge.

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