Top 32 Blockchain Interview Questions

Top 32 Blockchain Interview Questions: Here are the top interview questions of Blockchain. Be prepared for the interview. You can download the entire questions in a pdf format. so guys All the best for your interview.

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.


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

PointsBitcoin BlockchainEthereum Blockchain
FounderSatoshi NakamotoVitalik Buterin
Release Date9 Jan 200830 July 2015
Release MethodGenesis Block MinedPresale
UsageDigital CurrencySmart Contracts
CryptocurrencyUsedBitcoin Ether
AlgorithmSHA-256Ethash
Blocks Time10 minutes12-14 seconds
ScalableNot yetYes

3) What are the different types of Blockchains?

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 one is in charge, and anyone can read, write, and audit the blockchain. It is open source, therefore 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.

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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.

Q6) What exactly do you know about the security of a block?

Top 32 Blockchain Interview Questions Well, a block cannot be modified by all the users on a network. Therefore it offers an excellent level of security. In addition to this, every block is secured using cryptography that is another vote in this matter. Thus one needs not to worry about the safety as well as the security of data that is present in a block.

Q7) Is there any network specific conditions for using Blockchain technology in an organization?

There is no specific condition on using it. However, the network must be a peer-to-peer network under the concerned protocols.  It actually validates the new block simply and helps organizations to keep up the pace in this matter without investing in third-party applications.

Q8) What is encryption? What is its role in Blockchain?

Data security always matters. Encryption is basically an approach that helps organizations to keep their data secure. In this technique, the data is encoded or changed up to some extent before it is sent out of a network by the sender. The only receiver can understand how to decode the same. In Blockchain, this approach is useful because it simply adds more to the overall security and authenticity of blocks and helps to keep them secure.

Q9) Is it possible to modify the data once it is written in a block?

No, it is not possible to do so. In case any modification is required, the organization simply has to erase the information from all other blocks too. It is because of no other reason than this, data must be given the extreme care of while using this approach.

Q10) What type of records can be kept in Blockchain? Is there any restriction on same?

There is no restriction of keeping records of any type in the Blockchain approach. Presently, a lot of organizations all over the world are using this approach and the fact is records of medical transactions, events related to organizations, management activities, transaction processing, identity management, as well as documentation are the common type of records that can be kept on them. It must be noted that the record keeping is not just limited to these applications only.

11) Is it possible to modify the data once it is written in a block?

No, it’s not possible to do so. In case any modification is required, the organization simply has to erase the information from all other blocks too. It is because of no other reason than this, data must be given the extreme care of while using this approach.

12) What are Block Identifiers?

In Blockchain, blocks can be identified by the block header hash and the block height.

13) Is it possible in Blockchain to remove one or more block from the networks?

Yes, it can be done. There are times when only a specific portion of this online ledger is to be considered. With the help of default options and filters, this can easily be done without making a lot of efforts.

14) What exactly do you know about the security of a block?

Top 32 Blockchain Interview Questions Well, a block or the entire blockchain is protected by a strong cryptographic hash algorithm. Each block has a unique hash pointer. Any modification in the block constituents will result in the change in the hash identifier of the block.  Therefore, it offers an excellent level of security. Thus, one needs not to worry about safety as well as the security of data that is present in a block.

15) What are Merkle trees? How important are Merkle trees in Blockchains?

Merkle Tree also is known as ‘hash tree’ is a data structure in cryptography in which each leaf node is a hash of a block of data, and each non-leaf node is a hash of its child nodes.

The benefit of using the Merkle Tree in blockchain is that instead of downloading every transaction and every block, a “light client” can only download the chain of block headers.

Also, if someone needs to verify the existence of a specific transaction in a block, then he doesn’t have to download the entire block. Downloading a set of a branch of this tree which contains this transaction is enough. We check the hashes which are just going up the branch (relevant to my transaction). If these hashes check out good, then we know that this particular transaction exist in this block.

16) Which cryptographic algorithm is used in Blockchain?

Blockchain uses SHA-256 Hashing algorithm. SHA-256 Hashing algorithm was developed by the National Security Agency (NSA) in the USA.


17) In what order are the blocks linked in the blockchain?

In the blockchain, each and every block are always linked in a backward order, i.e., each block gets linked to its previous block.


18) What are the benefits of Blockchain that you know?

The important benefits for Blockchain are given below:

Settlement in real time: In the financial industry, blockchain can allowing the quicker settlement of trades. It does not take a lengthy process for verification, settlement, and clearance because a single version of agreed-upon data is available between all stack holders.

Cost saving: Blockchain allows peer-to-peer transactions to be completed without the need for a third party such as a bank which reduced overhead costs for exchanging assets.

Security and Resilience: Blockchain uses very advanced cryptography to make sure that the information is locked inside the blockchain that protects against hacking attacks and fraud. It uses Distributed Ledger Technology where each party holds a copy of the original chain, so the system remains operative, even the large number of other nodes fall.

Immutability: Blockchain register transactions in a chronological order which certifies the unalterability of all operations. It means when any new block has been added to the chain of ledgers, it cannot be removed or modified.

User Pseudonymity: Pseudonymity is the state in which a user has a consistent identifier that is not their real name. The real identities are only available to administrators. It allows users to communicate with others in a generally anonymous way. It helps to maintain user privacy and enables free transactions without any security worries. In Blockchain, your pseudonym is the address to which you receive Bitcoin. Every transaction which involves that address is stored forever in the blockchain. If your address is linked to your identity, every transaction will be linked to you. It was recommended that Bitcoin users every time use a new address for each transaction to avoid the transactions being linked to a common owner.


19) What are the Merkle trees? How important are Merkle trees in Blockchains?

Top 32 Blockchain Interview Questions Merkle tree is a fundamental part of blockchain technology. Merkle trees are a mathematical data structure trees in which every leaf node is labeled with the hash of a data block, and the non-leaf node is labeled with the cryptographic hash of the labels of its child nodes. The leaf nodes are the lowest nodes in the tree. Merkle trees serve as a summary of all the transactions in a block. It is also known as Hash Tree.

The Merkle tree in blockchain plays an important role when someone needs to verify the existence of a specific transaction in a block, then there is no need to download the entire block to verify the transaction in a block. He can only download the chain of block headers. Downloading a collection of a branch of this tree which contains this transaction is enough. We check the hashes which are relevant to my transactions. If these hashes check out good, then we know that this particular transaction exists in this block.


20) What is Double Spending? Is it possible to double spend in a Blockchain system?

Double spending means spending the same money multiple times. In physical currency, the double spending problem can never arise. But in digital cash-like bitcoin, the double spending problem can arise. Hence, in Bitcoin transactions, there is a possibility of being copied and rebroadcasted. This makes it possible that the same bitcoin could be spent twice by its owner. One of the primary aims of Blockchain technology is to eliminate this approach up to the possible extent.

Blockchain prevents the double spending problem by implementing a confirmation mechanism from multiple parties before the actual transaction is written to the ledger.

21) What is information processing according to you? What are the key challenges that are associated with it?

The information is often shared on a network. Before actually transmitting it over a network, it needs to be changed into formats that can fit the standards of the channels (channel is a link between sender and a receiver). The work done to convert the information at both sender and receiver end is generally regarded as information processing. The biggest challenge to information processing is securing it during that time. Another challenge is processing bulk information can impose a limit on performance.

22) What does BIP stands for?

It means Bitcoin improvement proposal.

23) Name some popular platforms for developing blockchain applications

After the development of bitcoin, various blockchain platforms started coming up. Ethereum came right after the evolution of Bitcoins and is one of the popular public platforms for building Blockchain based applications.

Then there is a Hyperledger community for building enterprise-based solutions. Also, Qtum, IOTA, EOS are some of the widely used platforms for building Blockchain.

24) What is Double Spending? Is it possible to double spend in a Blockchain system?

Top 32 Blockchain Interview Questions It’s a condition when one digital token is spent multiple times because the token generally consists of a digital file that can easily be cloned. It simply leads to inflation and organizations must bear a huge loss. One of the primary aims of Blockchain technology is to eliminate this approach up to the possible extent.

Blockchain prevents double spending by confirming a transaction by multiple parties before the actual transaction is written to the ledger. It’s no exaggeration to say that the entirety of bitcoin’s system of Blockchain, mining, proof of work, difficulty, etc, exist to produce this history of transactions that is computationally impractical to modify.

26) What is a security policy?

A security policy defines what exactly needs to be secured on a system. It bounds a network user under some core protocols that they all must agree and follow to enhance the overall security. When it comes to information or financial records of an organization, multiple security policies are implemented than just one. 

27) How you will handle the risk management when it comes to securing the transactions records?

It is basically a process of finding the threats and all the vulnerabilities to the financial records of an organization. The best thing that can be done against this approach is to take the right counter measures against them immediately. Another approach is to pay attention to a back-up plan. Based on the value of information, more approaches such as buying new risk management software can simply be considered. The prime risk to information is from black-hat hackers.

28) Name the common type of ledgers that can be considered by users in Blockchain?

These are:

  1. Centralized Ledgers
  2. Decentralized Ledgers
  3. Distributed Ledgers

29) How a blockchain ledger is different from an ordinary one?

Top 32 Blockchain Interview Questions The first and in fact the prime difference is Blockchain is a digital ledger that can be decentralized very easily. The chances of error in this approach are far less than that in an ordinary ledger. An ordinary ledger is what that is prepared with hands or by human efforts while the Blockchain performs all its tasks automatically. You just need to configure it in a proper manner and by following all the guidelines. 

30) A distributed digital ledger is used for recording transaction in BlockChain. What does the system rely on?

It rely on the network nodes.

31) How does the security of a block works?

A blockchain is a chain of blocks that contain records of transactions. It is the most secure part of a blockchain. The record of a blockchain is protected through a cryptographic hash algorithm. Each block is connected with all other blocks before and after it through a distinctive hash pointer which adds more security to the block. If the value within a block is modified, the hash value will also change. This is a security identifier and provides a reasonable level of security to the whole blockchain.

Ambitious hackers also need to know the hash key of the previous block to make changes to the block information. For those ambitious hackers, blockchains are decentralized and distributed across peer-to-peer networks that are continuously updated and keep syncing. Since these records are not contained in a central location, so blockchains don’t have a single point of failure and cannot be changed from a single computer.


32) What is the difference between public and private key?

Top 32 Blockchain Interview Questions A private key is used to encrypt or lock a message or a transaction that is sent on the blockchain network. The sender can send a message using the public key of the receiver. On the other hand, the receiver can decrypt the message or the transaction using his private key. By using the private and public key, the communication or transaction is kept safe and tamper-proof.