Blockchain Interview Questions and Answers | Blockchain Technology | Blockchain Tutorial | Edureka

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Agenda
Blockchain In Market
Advanced Blockchain Questions
General Blockchain Questions

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Blockchain Interview Questions

02
01 General Interview
Questions
Advanced Interview Questions

Blockchain: General Interview Questions
1. What do you know about Blockchain?

1. What do you know about Blockchain?
➢ Blockchain is a decentralized distributed database of immutable records
➢ The transactions are protected by strong cryptographic algorithms
➢ Every new record is validated across the distributed network before it is stored in a block
➢ To access the data of the first block, you have to traverse from the last created block to the first block

2. What is the principle on which blockchain technology is based on?

2. What is the principle on which blockchain technology is based on?
Blockchain is based on the Distributed ledger technology which aims to provide a shared single source of
truth being distributed across the network

3. What are the different types of Blockchains?

3. What are the different types of Blockchains?
Public
PrivateConsortium

4. Why is Blockchain a trusted approach?

4. Why is Blockchain a trusted approach?
➢ Blockchain is an immutable ledger. The transactional records are secured by strong cryptographic algorithms. Also,
every participants have the shared single source of truth
➢ It distributes trust among different actors in the system via an economic game that incentivizes actors to cooperate
with the rules defined by the protocol

5. What type of records can be kept in a Blockchain? Is there any restriction on same?

5. What type of records can be kept in a Blockchain? Is there any restriction on same?
There is no restriction on keeping records of any type in the Blockchain approach. Industries are using Blockchain for
securing all types of records.
The common types of records (to name a few) that can be kept on the Blockchains are:
➢ Records of medical transactions
➢ Identity management
➢ Transaction processing
➢ Business transactions,
➢ Management activities
➢ Documentation

6. Blockchain is a decentralized database. How does it differ from traditional databases?

6. Blockchain is a decentralized database. How does it differ from traditional databases?
Properties Blockchain Traditional Database
Records Records are stored in a decentralized database Records are centralized
Operations Only Insert Operations Can perform C.R.U.D. operations
Replication Full Replication of block on every peer
Master Slave
Multi-Master
Consensus Majority of peers agree on the outcome of transactions
Distributed Transactions
(2 phase commit)
Invariants Anybody can validate transactions across the network Integrity Constraints

7. What are the key features of Blockchain?

7. What are the key features of Blockchain?
Key features of blockchain:
➢ Decentralized Systems
➢ Distributed ledger
➢ Immutability
➢ Safer & Secure Ecosystem
➢ Minting (Blockchain specific)

8. What is encryption? What is its role in Blockchain?

8. 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.
The encrypted data is encoded or changed up to some extent before it is sent out of a network by the sender and only
authorized parties can access that information.
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.

9. What do you mean by blocks in the blockchain technology?

9. What do you mean by blocks in the blockchain technology?
Blockchain consists of a list of records. Such records are stored in blocks. These blocks are in turn linked with other blocks
and hence constitute a chain called Blockchain.
New BlocksTo access data of the first ever created block, you have to
traverse from the last created block to the first block

10. How does a block is recognized in the Blockchain approach?

10. How does a block is recognized in the Blockchain approach?
Every block in this online ledger basically consists of a hash pointer which acts as a link to the block which
is prior to it, transaction data and in fact a stamp of time.

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

11. Is it possible to modify the data once it is written in a block?
No, it's not possible to do so. As all the records are secured by strong cryptographic algorithms and any
change in any of the records will consequently result in the change in the hash of the records.

12. What are Block Identifiers?

12. What are Block Identifiers?
Block identifiers are the means to identify a block in the blockchain. The block 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 network?

13. Is it possible in Blockchain to remove one or more block from the network?
No, it can’t be done. Since all the blocks in the blockchain are linked to the hash of the previous block.
Removing any block from the blockchain will disrupt the header hash of all the previous blocks.

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

14. What exactly do you know about the security of a block?
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. Thus, one needs not to worry about the 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?

15. What are Merkle trees? How important are Merkle trees in Blockchains?
Merkle Tree also 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.
Merkle Root
Merkle Tree
Block

16. What is a ledger? Is Blockchain an incorruptible ledger?

16. What is a ledger? Is Blockchain an incorruptible ledger?
Blockchain is considered incorruptible
“To take over the network, an attacker would have to control more than 50 percent of its total computing
power,”
Augier explains. “We hope that’s a theoretical scenario, but we can’t be sure. Should it happen, the
individual would take every precaution to avoid being noticed.” Not to mention the energy required to
power the computers needed for the blockchain system to work.

17. Name the common type of Network systems that are extensively being used in various applications?

18. How is a blockchain ledger different from an ordinary one?

18. How is a blockchain ledger different from an ordinary one?
Blockchain Ledger Ordinary Ledger
Same copy of the ledger exist in the entire
system
The ledger may or may not be the same in
the system
The chances of error are less The chances of error are more
Only read and create option exists.
Anything once written cannot be altered
You can perform all CRUD operations in
such ledgers

19. What do you mean by mining?

19. What do you mean by mining?
Mining is the process of adding transaction records to Bitcoin's public ledger of past transactions
➢ Miners are special Nodes which hold the copy of the ledger and verifies the transactions happening in the
network
➢ Using state of the art cryptographic algorithm, miners validates the transactions across the network

20. A distributed digital ledger is used for recording transaction in Blockchain. What does the
system rely on?

The system relies on the nodes of the network. The nodes in the blockchain network are responsible for
the security and smooth running of the system.
20. A distributed digital ledger is used for recording transaction in Blockchain. What does the
system rely on?

21. Can You explain the components of Blockchain Ecosystem?

21. Can You explain the components of Blockchain Ecosystem?
Shared Ledger
A data structure(Ledger) is managed inside the
node application. Contents for the ecosystem
can be viewed, once the node application is in
running state
Consensus Algorithm
Implemented as part of the node application.
Provides the rule for how the ecosystem will
arrive at a single view of the ledger
Node Application
Each Node have to install and run a computer
application definitive to the ecosystem they wish to
participate in.
Example- In bitcoin ecosystem, each computer must be
running the bitcoin wallet
Virtual Machine (Smart Contract Functionality)
An abstraction of a machine operated with instructions
and Implemented as part of the node application that
every participant in the ecosystem runs

22. State difference between proof-of-work & proof-of-stake?

23. Name some popular platforms for developing blockchain applications

23. Name some popular platforms for developing blockchain applications
Corda
Hyperledger FabricEthereum
Quorum
Cardano
IOTA

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

24. What is Double Spending? Is it possible to double spend in a Blockchain system?
Double Spending: 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.
Blockchain prevents double spending by
confirming a transaction by multiple parties
before the actual transaction is written to the
ledger.

25. What are the benefits of Blockchain that you know?

Settlement in real time
Cost Saving
Security & Resilience
Immutability
User Pseudonymity
25. What are the benefits of Blockchain that you know?

02
01 General Interview
Questions
Advanced Interview
Questions

Blockchain: Advanced Interview Questions
1. Can you tell me some of the widely used cryptographic algorithms?

1
5
4
2
3
Like blowfish, twofish is also a
symmetric technique with keys of length
256 bits
Twofish
RSA is a public-key encryption
algorithm and the standard for
encrypting data sent over the internet
RSA
uses keys of 192 and 256 bits for heavy
duty encryption purposes. It is largely
considered impervious to all attacks
AES
Known for its speed and effectiveness
symmetric cipher splits messages into blocks of
64 bits and encrypts them individually
Blowfish
Triple DES uses three individual keys
with 56 bits each. The total key length
adds up to 168 bits
Triple DES
1. Can you tell me some of the widely used cryptographic algorithms?

2. What do you know about forking in Blockchain? Name the types of forking

2. What do you know about forking in Blockchain? Name the types of forking
In cryptocurrencies, a fork is a situation when a blockchain diverges into two potential paths forward, with regard to
transaction history or a new rule about valid transactions.
There are two types of forks in Blockchains:
Hard fork: A hard fork is a rule change such that the software enforcing the old rules will see the blocks adhering to
the new rules as invalid
Soft fork: A soft fork is a change of rules that creates blocks recognized as valid by the old software, i.e. it
is backwards-compatible. As soft fork can also split the blockchain when non-upgraded software creates blocks not
considered valid by the new rules

3. Explain the significance of blind signature and how it is useful?

3. Explain the significance of blind signature and how it is useful?
Blind Signatures
➢ It is a form of digital signature in which the content of a message is disguised (blinded)
before it is signed
➢ The resulting blind signature can be publicly verified against the original, unblinded
message in the manner of a regular digital signature
Blind signatures are typically employed in privacy-related protocols where the signer and
message author are different parties
Examples include cryptographic election systems and digital cash schemes.

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

4. What is Secret Sharing? Does it have any benefit in Blockchain technology?
Secret Sharing
➢ In Blockchain technology it 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 participant to whom a share of the secret is allocated
agree to combine them together with others

5. Can you explain what are off-chain transactions?

5. Can you explain what are off-chain transactions?
An off-chain transaction is the movement of value outside of the blockchain.
While an on-chain transaction - usually referred to as simply 'a transaction' - modifies the
blockchain and depends on the blockchain to determine its validity, an off-chain transaction
relies on other methods to record and validate the transaction.

6. What do you mean by Anonymity and Pseudonymity in cryptocurrency?

6. What do you mean by Anonymity and Pseudonymity in cryptocurrency?
Anonymity:
The state or quality of being anonymous. Not bound or linked to any entity
Being anonymous in cryptocurrency makes it harder to trace transactions and giving higher level of privacy
Example: Zcash
Pseudonymity:
A pseudonym is a unique identifier(example-nick name, credit card numbers, student numbers, bank account
numbers, etc.)
All the transactions in pseudonymous network are open and visible to all and thus, it is widely acceptable

7. How does peer discovery work in peer to peer (p2p) network?

7. How does peer discovery work in peer to peer (p2p) network?
When a new node boots up, it doesn’t know anything about the network, because there is no central
server. Usually developers provide a list of trusted nodes written directly into the code that can be used for
initial peer discovery.

8. What is 51% attack?

➢ It is a situation where a group of miners who hold more than 50% of the Network Hash Rate could manipulate
with the New transactions (Stopping the transactions to proceed or gaining conformations) or
➢ Able to reverse the transactions that were recently confirmed and kind of doing Double spend. It is Highly
unlikely to be able to do that today but it is possible
8. What is 51% attack?

9. Name organizations that can use Blockchain technology?

➢ There is no strict upper limit on the category of business who can consider this approach.
➢ The fact is almost all the businesses are engaged in online or financial transactions that they need to make to run
the processes smoothly.
➢ Large-scale corporations, financial institutions, private businesses, government departments and even defence
organizations can trust this technology very easily.
9. Name organizations that can use Blockchain technology?

10. What are the core requirements for a Business Blockchain?

10. What are the core requirements for a Business Blockchain?
visibility;

11. What are the key principles in Blockchain that are helpful in eliminating
the security threats that needs to be followed?

11. What are the key principles in Blockchain that are helpful in eliminating
the security threats that needs to be followed?
There are a few principles that need to be followed with respect to time. They are:
1. Auditing
2. Securing applications
3. Securing testing and similar approaches
4. Database security
5. Continuity planning
6. Digital workforce training
All these principles are basic and are easy to implement. They are helpful in making the transactions records useful.

12. Is the Blockchain Different from Banking Ledgers?

12. Is the Blockchain Different from Banking Ledgers?
Banks and accounting systems use
ledgers to track and timestamp
transactions. The difference is that the
Blockchain is completely decentralized
and an open source.
Furthermore, the Blockchain, because of
its open-source nature, is more versatile
and programmable than central banking
ledgers.

13. Can you list some of the popular consensus algorithms? Why we need
different consensus mechanisms?

13. Can you list some of the popular consensus algorithms? Why we need
different consensus mechanisms?
Some of the popular consensus algorithms are:
➢ PBFT (Practical Byzantine Fault Tolerance)
➢ Proof-of-work
➢ Proof-of-stake
➢ Delegated proof-of-stake
➢ Proof-of-elapsed time
Now, the possible reasons why we need consensus mechanism
more than "proof-of-work" are“
• Different business needs
• Different use cases
• Also:
• Cryptography/Strength of Algorithm
• Regulation requirements
• Implementation
• Performance
• Tokenization
• Security
• Privacy

14. Is there any network specific conditions for using Blockchain technology in
an organization?

14. Is there any network specific conditions for using Blockchain technology in
an organization?
There is no specific condition of using it. However, the network must be a peer-to-peer network under the concerned
protocols. It validates the new block simply and helps organizations to keep up the pace in this matter without
investing in third-party applications.

15. Name the steps that are involved in the Blockchain project implementation?

Well, there are total six steps involved in this process and they are:
➢ Decide whether to use an existing blockchain or you need to create a new blockchain for your business
➢ Requirement identification
➢ Screen ideas consideration
➢ Project development for Blockchain
➢ Feasible study on the security
➢ Implementation
➢ Controlling and monitoring the project
15. Name the steps that are involved in the Blockchain project implementation?

16. Explain a real-life use-case where Blockchain is being used?

16. Explain a real-life use-case where Blockchain is being used?
➢ Storj is like an internet
filesystem
➢ Data blocks are encrypted
and distributed across a
globally distributed set of
storage nodes using block-
chain algorithm

17. What are side chains?

17. What are side chains?
Sidechains are separate blockchains which is connected to other blockchains through the use of two-way peg which
allows transfer of digital coins or assets between blockchains at a fixed or otherwise deterministic exchange rate.

18. Can you name one major limitation of Blockchains?

18. Can you name one major limitation of Blockchains?
Scalability problems are the main thing restraining the excitement around blockchain technology.
With increasing popularity of cryptocurrencies, transactions have increased considerably over the years.
While it was manageable when the number of transactions was less, as they have gotten more popular a host of issues
have come up.
Issue of scalability is the major problem because of two reasons:
➢ The time is taken to put a transaction in the block
➢ The time is taken to reach a consensus

19. Are there alternatives to Blockchains?

19. Are there alternatives to Blockchains?
➢ There are some alternative technologies which are much faster and don’t have a scalability problem
➢ The most impressive is the Hashgraph
➢ It’s a little bit more centralized than the blockchain but not as wasteful and maybe it’s the only way to apply
decentralized technology to wide industries

20. Do you know the means to scale Blockchain?

20. Do you know the means to scale Blockchain?
Following could be some of the solutions, depending upon the Blockchain protocols:
➢ The Lightening Network: Proposed solutions to Bitcoins scalability. This is possible due to the fact that Lightning
Network doesn’t require every individual transaction to be recorded on the blockchain
➢ Segwit: Segwit (exclusive to Bitcoins) would mean that all the signature data of each and every transaction will move
from the main chain to the side chain
➢ Block Size Increase: With increasing transactions (particularly in Bitcoins & Ethereum), the possible solution is to
increase the block size to accommodate more transactions
➢ Sharding: Means separating the blockchain data in several sets, and storing only one of these sets.
In Monero’s example, if there were a set for blocks with an even block height and a set for odd block height
your Monero daemon could store the data for blocks with an even block height only

21. With Blockchain came the web 3.0. Can you name some decentralized Blockchain
based applications that will bring about the next level of the internet

21. With Blockchain came the web 3.0. Can you name some decentralized Blockchain
based applications that will bring about the next level of the internet
Web 3.0Web 2.0

Blockchain Interview Questions and Answers | Blockchain Technology | Blockchain Tutorial | Edureka

Blockchain Interview Questions and Answers | Blockchain Technology | Blockchain Tutorial | Edureka

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