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Blockchain Interview Questions

Cracking the Blockchain interview questions signifies, the interviewee has opened the gateway to fortune and success. However, most of the candidates fail to find success in Blockchain interviews due to tricky questions asked by the interviewers. Keeping in view the trouble of inexperienced candidates, our Aptrong's Blockchain specialists, Blockchain experts, and Blockchain trainers have drafted a questionnaire comprised of Blockchain interview questions and answers for freshers and experienced candidates. Giving the relevant answers to Blockchain interview question can lend a hand in deciding the providence of the candidates.

blockchain interview questions

About Blockchain

A Blockchain is an increasing list of records linked utilizing cryptography. Each cryptographic hash comprises of the previous block, a timestamp, and transaction data. Blockchain is defiant to modification of the data. Blockchain, an open distributed ledger can witness transactions between two parties competently and in a demonstrable and permanent way. Blockchain is characteristically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any known block cannot be altered retroactively without alteration of all following blocks, which needs consensus of the network majority.

Blockchain Interview Questions And Answers

1. What is Blockchain?

A Blockchain is a constantly growing ledger(file) that keeps a permanent record of all the transactions that have taken place, in a secure, chronological, and immutable way. It can be used for the secure transfer of money, property, contracts, etc. without requiring a third-party intermediary like bank or government.

Blockchain is the backbone of the most famous cryptocurrency named Bitcoin. It is a peer to peer electronic cash system and a decentralized network which allows users to make transactions directly without the involvement of third-party to manage the exchange of funds.

2. What is the difference between Bitcoin blockchain and Ethereum blockchain?

We can see the basic differences between Bitcoin blockchain and Ethereum blockchain in the below table.

Points Bitcoin Blockchain Ethereum Blockchain
Founder Satoshi Nakamoto Vitalik Buterin
Release Date 9 Jan 2008 30 July 2015
Release Method Genesis Block Mined Presale
Usage Digital Currency Smart Contracts
Cryptocurrency Used Bitcoin Ether
Algorithm SHA-256 Ethash
Blocks Time 10 minutes 12-14 seconds
Scalable Not yet Yes

3. What are the different types of Blockchains?

The different types of blockchains which introduce to the world are:

There are mainly three types of Blockchains introduced to the world.

1. Public Blockchain

A Public blockchain is a kind of blockchain which is "for the people, by the people, and of the people." There is no in-charge it means anyone can read, write, and audit the blockchain. It is an open-source, distributed, and decentralizes public ledger so anyone can review anything on a public blockchain. They are considered to be Permissionless blockchain.

2. Private Blockchain

A Private blockchain is a private property of an individual or an organization. It is controlled by a single organization that determines who can read it, submit the transaction to it, and who can participate in the consensus process. They are considered to be permissioned blockchain.

3. Consortium Blockchain or Federated Blockchain

In this blockchain, the consensus process is controlled by a pre-selected group, i.e., group of companies or representative individuals. These pre-selected group is coming together and making decisions for the best benefit of the whole network. Such groups are also called consortiums or a federation that's why the name consortium or federated blockchain.

4. Where is a blockchain stored?

The blockchain can be either stored as a flat file or as a database.

5. What are the types of records that are present in the blockchain database?

There are two types of records in a blockchain database.

  1. Transactional Records
  2. Block Records

Both the records can easily be accessed and can integrate with each other without following any complex algorithm.

6. List the key features of blockchain?

The essential properties of a blockchain are:

  1. Decentralized Systems
  2. Distributed ledger
  3. Safer & Secure Ecosystem
  4. Fast
  5. Low Transaction Fees
  6. Fault-Tolerant
  7. Minting

7. How does Blockchain differ from relational databases?

The blockchain differs from the relational database in the following ways.

Points Blockchain Relational Database
Unit of data Block Table
Failure None Can happen
Centralized Control No Yes
Modification in data Not Possible Possible
Single Point of Failure Does not exist Exists

8. Name some popular platforms for developing blockchain applications.

Some of the popular platforms for developing blockchain are:

  1. Ethereum
  2. Hyperledger Sawtooth
  3. Quorum
  4. Ripple
  5. R3 Corda
  6. Qtum
  7. IOTA
  8. EOS

9. Every block of Blockchain consist of what elements?

Every block must include these three things:

  1. A hash pointer to the previous block
  2. Timestamp
  3. List of transactions

10. How can blocks be identified?

Blocks can be identified by their block height and block header hash.

11. Can you modify the data in a block?

No, it's not possible to modify the data in a block. In case any modification is required, you would have to erase the information from all other associated blocks too.

12. What is encryption? Does it have a role to play in blockchain?

Encryption is a process that helps the owner to keep his data safe. As data security always has been a challenge, organisations heavily rely on encryption for data security.

Encryption as a process has a unique methodology. It changes the data and encodes it when it is sent out on a network. This ensures that only authorised people can access its information.

Yes, Blockchain heavily relies on it as a process and an approach to secure data. Blocks become secure and remain authentic though this approach.

13. We spoke about securing blocks, what are these blocks?

Records that form the core of data in a Blockchain are stored in blocks. These blocks, when linked to other blocks, create a chain which is called Blockchain. So, the blocks are the basic elements that come into existence by amalgamation of data.

14. Is there a difference between Wei and Ether?

Yes, there is a difference between Wei and Ether based on their value. We can say that many Wei comes and add themselves up to create an Ether. To make it simpler, Wei is like currency, and 1 Ether or 1 ETH = 1018 Wei

At some point, the blockchain interview questions are going to get a bit complex. For a fresher, a lot of questions asked would be theoretical. This helps to understand the clarity of concepts of a candidate.

15. What is a Security Policy?

One general advice while taking a blockchain interview is that you need to be sorted and confident about what you say. It is okay to pass on a question or to mention that you are only guessing if you are unsure about any particular one. It really gives you a chance to relax and be authentic.

Coming back to the question, answering this one is pretty simple. Security Policy defines the things that need to be secured on a system. It binds a user within some protocols that it must agree to and follow. This enhances overall security. Usually, it is observed with crucial information, a layer of security policies is implemented.

16. Is RSA a secure algorithm?

Yes, RSA is a very secure algorithm. But there are different ways that this algorithm is attacked. It may be attacked by brute force, and occasionally attacked mathematically.

17. What are off chain transactions?

Off Chain Transactions are the movements of value that are placed outside the blockchain. While a simple transaction or an on-chain transaction modifies blockchains apart from depending on the blockchain to determine the validity. The off-chain transactions rely on other methods to validate transactions and even record them.

18. Are there any network-specific conditions for employing Blockchain technology in an organization?

There are no network-specific conditions for employing Blockchain. However, the network must be a peer-to-peer network under specific protocols. Blockchain approves the new blocks easily and helps the organizations to keep up the pace without investing in third-party applications.

19. What are the major elements of the blockchain ecosystem?

The blockchain has four major elements:

  • Shared ledger - It is decentralized in nature and is a central component of the blockchain.
  • Node application - It is a software that lets your computer connect with the blockchain. Ex: Bitcoin uses the bitcoin wallet application to detect each mode on the network.
  • Virtual application - It handles all the tasks that blockchain undertakes.
  • Consensus algorithm - This is used for managing blockchain rules through which each node can come to a conclusion.

20. What is the difference between a centralized network, decentralized network, and distributed ledger?

  • Distributed ledger: It is a shared ledger and is not controlled by any central authority. It is decentralized by nature and acts as a database for financial, legal or electronic assets.
  • Centralized network: A centralized network has a central authority to facilitate its operations.
  • Decentralized network: The nodes connected in the decentralized network are not dependent on the single server point, and each node holds the entire copy of the network configurations.

21. What is the difference between a scriptPubKey and P2SH address?

  • A scriptPubKey is found in transaction output and also known as a locking script.
  • The P2SH address is a special type of address, i.e., it is used for replacing complex locking scripts with its hash. In addition to the unlocking scripts, the transactions must contain the script that matches the hash.

22. What is Mining?

In the context of blockchain technology, mining is the process of adding transactions to the large distributed public ledger by providing the proof of work to the network, i.e., generated block is valid. It also adds new coins to the generated block. The term mining is best known for its association with bitcoin.

23. Is Blockchain an incorruptible ledger?

Blockchain ledger cannot be corrupted as per the developer’s claim.

24. What is Transparent and incorruptible in blockchain?

The blockchain network lives in a state of consensus, one that automatically checks in with itself every ten minutes. A kind of self-auditing ecosystem of a digital value, the network reconciles every transaction that happens in ten-minute intervals. Each group of these transactions is referred to as a “block”. Two important properties result from this:

Transparency data is embedded within the network as a whole, by definition it is public. It cannot be corrupted altering any unit of information on the blockchain would mean using a huge amount of computing power to override the entire network.

25. What is Blockchain Durability and robustness?

Blockchain technology is like the internet in that it has a built-in robustness. By storing blocks of information that are identical across its network, the blockchain cannot:

  1. Be controlled by any single entity.
  2. Has no single point of failure.

Bitcoin was invented in 2008. Since that time, the Bitcoin blockchain has operated without significant disruption. (To date, any of problems associated with Bitcoin have been due to hacking or mismanagement. In other words, these problems come from bad intention and human error, not flaws in the underlying concepts.)

The internet itself has proven to be durable for almost 30 years. It’s a track record that bodes well for blockchain technology as it continues to be developed

26. What is Secret Sharing? Does it have any benefit in Blockchain technology?

It is a well-understood that security matters a lot in digital transactions. Secret sharing in Blockchain technology is an approach that divides secret or personal information into different units and sent them to the users on the network. The original information can only be combined when a member to whom a share of the secret is allocated agree to combine them together with others. There are several security-related advantages it can offer in Blockchain technology.

27. Compare Blockchain with relational database

Criteria Blockchain RDBMS
Unit of data Block Table
Single point of failure Does not exist Exists
Centralized control No Yes
Editing/deleting data Not possible Possible

28. How is hard fork different from the soft fork in blockchain?

  • A hard fork in blockchain refers to a radical change to the software protocol, that makes previously invalid transactions/blocks valid. It requires all the users/nodes to upgrade to the latest software protocol.
  • Soft fork refers to a change to the software protocol that makes previously invalid transactions/blocks invalid.

29. What is a trapdoor function in blockchain development?

A trapdoor function is a one-way function, i.e., easy to compute in one direction but hard to compute in the opposite direction unless you have the special information. These functions are essential for public-key encryption and are most widely used in blockchain development to represent the ideas of addresses and private keys.

30. What is a 51% attack?

A 51% attack or double-spend attack refers to an individual or group of miners on a blockchain who try to control more than 50% of the network’s mining hash rate or computing power. These attackers try to prevent the new transactions from gaining confirmations and enable them to halt payments between some or all the users. They are also capable of reversing transactions that are completed while they are in control of the network; it means they could double-spend coins.

31. What is the difference between Proof-of-Stake and Proof-of-Work?

  • Proof-of-Work is the original Consensus algorithm in the blockchain. It is used for confirming transactions and producing new blocks to the chain. In this miners compete with each other to complete the transactions on the network and get rewarded.
  • Proof-of-Stake makes the consensus mechanism completely virtual. In this, a set of nodes decide to stake their cryptocurrencies of the transaction validation.

32. What is double-spending?

Double-spending is considered to be a potential flaw in digital cash scheme because the same digital tokens are used multiple times. The tokens generally consist of digital files that can be easily cloned. Bitcoin users protect themselves from double-spending frauds by waiting for confirmations while making payments on the blockchain; the transactions become more irreversible as the confirmations rise.

33. What is a blind signature?

A blind signature is a form of digital signature in cryptography where the content of the message is blinded before it is signed or considered. It is mostly used in privacy-related protocols where the author and signing parties are different. It is a verified approach.

Ex: Digital cash scheme

34. What is Cryptocurrency?

A cryptocurrency is a digital asset which can be used as a medium of exchange for conducting financial transactions using cryptographic functions. Cryptocurrencies leverage blockchain technology to gain transparency, decentralization, and immutability. Cryptocurrencies can be sent directly between two parties using public and private keys with minimal processing fees.

35. What is Consensus algorithm?

A consensus algorithm is a method through which all the peers of the blockchain network reach a standard agreement of the present state of a distributed ledger. It achieves high reliability and establishes trust between unknown peers in the distributed computing environment.

36. What are the types of consensus algorithms?

The most popular consensus algorithms available are listed below:

  • Proof-of-Work(PoW)
  • Proof-of-Capacity (PoC)
  • Proof-of-Activity (PoA)
  • Delegated Proof-of-Stake(DPoS)
  • Proof-of-Stake(PoS)
  • Proof-of-Authority
  • Proof-of-Burn
  • Unique Node Lists
  • Proof-of-Weight
  • Proof-of-Elapsed Time
  • Byzantine Fault Tolerance

Career scopes and salary scale

Every business sector in trending scenario is witnessing the employment crisis. However, when it is about Blockchain sector, the jobs’ seekers in the concerning subject are moving ahead in their profession. Blockchain has occupied the topmost place in the arena. The need of the aspirants in companies such as advertisement, designing, entertainment, fashion, video games, SME, publishing, etc is always at the demanding side. Therefore, when it is about career scope in the field, it is at brighter side for the candidates.

A newly joined Blockchain candidate in an organization can expect a minimum salary of 30,000 dollars per annum. The salaries are very reliant upon the location, business, and the company’s requirements.


This article has drafted intelligent answers to all Blockchain interview questions that are often asked in most of the advanced Blockchain interview questions. It draw near in Blockchain interview questions for experienced is being projected by our trainers and team of consultants. They have put their hard efforts and top of the acquaintance to aid candidates in getting answers to all doubts and not clear perceptions. Even then, if learners still require more detailing about Blockchain, they may drop in a message to our experts related to Blockchain interview questions for experienced professionals. Our trainers would be happy to help and resolve all your Blockchain programming issues of the students. Join Blockchain Training in Noida, Blockchain Training in Delhi, Blockchain Training in Gurgaon

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