About Blockchain
With the popularity of Blockchain increasing every day and new jobs opening up in the area, it is important to know how you can prepare for Blockchain interviews to land your dream job. This article (and the attached video) will take you through some of the key questions and their answers that you should be prepared for. Let’s take a look.
Blockchain Interview Questions – Beginner Level
Differentiate between Blockchain and Hyperledger.
Blockchain is a decentralized technology of immutable records called blocks, which are secured using cryptography. Hyperledger is a platform or an organization that allows people to build private Blockchain.
How do you explain Blockchain technology to someone who doesn’t know it?
Let’s consider the example of a school where Blockchain is similar to a digital report card of a student. Say, each block contains a student record that has a label (stating the date and time) of when the record was entered. Neither the teacher nor the student will be able to modify the details of that block or the record of report cards. Also, the teacher owns a private key that allows him/her to make new records and the student owns a public key that allows him to view and access the report card at any time. So basically, the teacher owns the right to update the record while the student only has the right to view the record. This method makes the data secure.
What is Merkel Tree?
Merkel Tree is a data structure that is used for verifying a block. It is in the form of a binary tree containing cryptographic hashes of each block. A Merkle tree is structured similarly to a binary tree where each leaf node is a hash of a block of transactional data and each non-leaf node is a hash of its leaf node. The Merkel root or hash root is the final hash root of all the transaction hashes. It encompasses all the transactions that are underlying all the non-leaf nodes.
What do you mean by blocks in Blockchain technology?
Blockchain is a distributed database of immutable records called blocks, which are secured using cryptography. Refer to the video to see the various attributes of a block.
There are a previous hash, transaction details, nonce, and target hash value. A block is like a record of the transaction
How is Blockchain distributed ledger different from a traditional ledger?
- A Blockchain distributed ledger is highly transparent as compared to a traditional ledger.
- Blockchain distributed ledgers are irreversible. Information registered on a distributed ledger cannot be modified whereas on a traditional ledger it is reversible.
- A distributed ledger is more secure. It uses cryptography and every transaction is hashed and recorded whereas in traditional ledger security can be compromised.
- In a distributed ledger, there is no central authority. It is a distributed system and the participants hold the authority to maintain the sanity of the network and are responsible for validating the transactions
How can you identify a block?
Every block consists of four fields –
- The hash value of the previous block (thereby getting linked in a blockchain)
- It contains details of several transaction data
- It has a value called the nonce. The nonce is a random value which is used to vary the value of the hash in order to generate hash value less than the target
- Hash of the block itself. It is the digital signature of the block and an alphanumeric value used to identify a block
What is cryptography? What is its role in Blockchain?
Blockchain uses cryptography to secure users’ identities and ensure transactions are done safely with a hash function.
What are the different types of Blockchain?
There are three different types of Blockchain – Public, Private, and Consortium Blockchain.
Public Blockchain ledgers are visible to all the users on the internet and any user can verify and add a block of transactions to the Blockchain. Examples, Bitcoin, and Ethereum.
What happens when you try to deploy a file with multiple contracts?
In Blockchain, deploying a file with multiple contracts is not possible. The compiler only deploys the last contract from the uploaded file and the remaining contracts are neglected.
What is a Genesis Block?
- The genesis block is the first block in the Blockchain which is also known as block 0
- In Blockchain, it is the only block that doesn’t refer to its previous block.
- It defines the parameters of the Blockchain such as,
- level of difficulty,
Blockchain Interview Questions – Intermediate Level
How is the hash (Block signature) generated?
The process of generating a block signature involves:
- Passing transaction details through a one-way hash function i.e., SHA-256.
- Running the output value through a signature algorithm (like ECDSA) with the user’s private key.
List down some of the extensively used cryptographic algorithms.
Here are a few popular algorithms:
- SHA – 256
- RSA (Rivest-Shamir-Adleman)
- Triple DES
- Ethash
- Blowfish
What is a smart contract and list some of its applications?
Smart contracts are self-executing contracts which contain the terms and conditions of an agreement between the peers
Some of the applications are:
Transportations: Shipment of goods can be easily tracked using smart contracts
Protecting copyrighted content: Smart contracts can protect ownership rights such as music or books
What is the Ethereum network and how many Ethereum networks are you familiar with?
Ethereum is a blockchain-based distributed computing platform featuring smart contract functionality that enables users to create and deploy their decentralized applications
There are three types of networks in Ethereum:
- Live network (main network) – Smart contracts are deployed on the main network
- Test network (like Ropsten, Kovan, Rinkeby) – Allow users to run their smart contracts with no fees before deploying it on the main network
Where do nodes run a smart contract code?
Nodes run smart contracts code on Ethereum Virtual Machine (EVM). It is a virtual machine designed to operate as a runtime environment for Ethereum-based smart contracts.
EVM is operated in a sandboxed environment (isolated from the main network). This is a perfect testing environment.
You can download the EVM, run your smart contract locally in an isolated manner and once you have tested and verified it, you can deploy it on the main network
What is a Dapp and how is it different from a normal application?
Dapp:
- A Dapp is a decentralized application which is deployed using smart contract
- A Dapp has its back-end code (smart contract) which runs on a decentralized peer-to-peer network
- Process:
- Front-end
- Smart contract (backend code)
- Blockchain (P2P contract)
Name some leading open source platforms for developing Blockchain applications.
- Ethereum is one of the popular platforms for building Blockchain-based applications
- Eris is used for building enterprise-based solutions
Some of the other widely used platforms for building Blockchain include Hyperledger, Multichain, Open chain.
What is the very first thing you must specify in a Solidity file?
It is necessary to specify the version number of Solidity at the beginning of code as it eliminates incompatibility errors that can arise while compiling with another version. This is a mandatory clause that has to be there at the top of any Solidity code you write. You also need to mention the correct version number for the code.
What is the nonce and how is it used in mining?
In Blockchain, mining is a process to validate transactions by solving a difficult mathematical puzzle called proof of work. Now, proof of work is the process to determine a number (nonce) along with a cryptographic hash algorithm to produce a hash value lower than a predefined target. The nonce is a random value that is used to vary the value of hash so that the final hash value meets the hash conditions.
Blockchain Interview Questions – Expert Level
Name the steps that are involved in the Blockchain project implementation.
Requirement identification:
- Identify the problem and goal
- Identify the most suitable consensus mechanism
- Identify the most suitable platform
- Account for implementation and deployment costs
Planning stage
- In this stage and individual evaluates all requirements and decides a suitable blockchain platform to be implemented.
Development and implementation of a project
- Designing the architecture
- Designing the user interface
- Building the APIs
Controlling and monitoring the project
- Applying Proof of Concept (POC)
- Identifying and fixing issues
Explain a real-life use-case where Blockchain is being used.
In supply chain management, smart contracts provide permanent transparency and validation of transactions shared by multiple supply chain partners. Check out our diagrammatic display of supply chain management using Blockchain in our video.
What happens if the execution of a smart contract costs more than the specified gas?
Initially, your transaction will be executed, but if the execution of a smart contract costs more than the specified gas, then the miners will stop validating your contract. The Blockchain will record the transaction as failed, also the user doesn’t get a refund.
What does the gas usage in a transaction depend on and how is the transaction fee calculated?
Gas usage depends upon the amount of storage and set of instructions (codes) used in a smart contract. The transaction fee is calculated in Ether, which is given as:
Ether = Tx Fees = Gas Limit * Gas Price
What is the fork? What are some of the types of forking?
In simple terms, updating a cryptocurrency protocol or code is called forking. Fork implies that a Blockchain splits into two branches. It can happen when the participants of the network cannot come to an agreement with regards to the consensus algorithm and new rules to validate transactions.
There are three types of forking:
- Hard forks
- Soft forks
- Accidental forks
Differentiate between Proof of Work vs Proof of Stake.
Proof of Work (PoW):
In Blockchain, PoW is the process of solving a complex mathematical puzzle called mining. Here, the probability of mining a block is based upon the amount of computational work done by a miner. Miners spend a lot of computing power (with hardware) for solving the cryptographic puzzle.
Proof of Stake (PoS):
PoS is an alternative to PoW in which the Blockchain aims to achieve distributed consensus. The probability of validating a block relies upon the number of tokens you own. The more tokens you have, the more chances you get to validate a block. It was created as a solution to minimize the use of expensive resources spent in mining.
What is a 51% attack?
In Blockchain, a 51% attack refers to a vulnerability where an individual or group of people controls the majority of the mining power (hash rate). This allows attackers to prevent new transactions from being confirmed. Further, they can double-spend the coins. In a 51% attack, smaller cryptocurrencies are being attacked.
What are function modifiers in Solidity? Mention the most widely used modifiers.
In Solidity, function modifiers are used to easily modify the behavior of your smart contract functions. In simple terms, it can build additional features or apply restrictions on the function of smart contracts. The most extensively used function modifiers in solidity are:
- View, which are functions that cannot modify the state of a smart contract. They are read-only functions. Refer to our video to see an example of a View function
- Pure, which are functions that neither read nor write the state of a smart contract. They return the same result determined by its input values. Refer to our video to see an example of a Pure function
Conclusion
With these blockchain interview questions and answers, we hope you will be able to sail through your blockchain interview with confidence. However, if you want to dive deep check out our tutorial on blockchain and our Blockchain Certification Training Course that will help you achieve thorough expertise in the technology.
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