Interview Questions and Answers for Blockchain Developers

Blockchain is now more popular than it has ever been. The demand for blockchain developers is increasing as more projects utilise this technology at various levels. This article will assist you in defining the most crucial blockchain developer interview questions and identifying the best candidate for your decentralised network.


Vacancy Challenges for Blockchain Developers

The popularity of blockchain is at an all-time high. Any newspaper item that discusses this technology or anything linked to it attracts further attention: Bitcoin, digital currency, smart contracts, transaction security, data exchange, blockchain interview questions, and so on. As a result, an increasing number of projects, corporations, and organisations are integrating blockchain at various levels, increasing the demand for blockchain developers.


Finding the right applicant and developing the right blockchain interview questions in such difficult circumstances might be difficult. First and foremost, given the scarcity of individuals on the market and the freshness of the sector, a lack of experience in this field should not be considered a negative. A good developer, especially one with a solid technical foundation, will be able to grasp this technology in a short amount of time. Middle-aged developers who write in Java, C / C ++, Go, Python, and Rust are eager to learn and apply their skills in the field of digital currency.



It is preferable to recruit developers from the rapidly expanding bitcoin blockchain ecosystem. Such experts attend a variety of conferences, meetups, and other events in order to further their education. The bitcoin community is currently working on new ideas for digital money technologies.


Talented graduates of top technical universities are another intriguing resource. Winners of international olympiads in mathematics and programming should be given special consideration; a flair for handling non-standard problems substantially facilitates work with blockchain. The availability of knowledge in the field of applied cryptography will be a significant benefit.



A creative attitude and ambition, in addition to professionalism and mathematical aptitude, are crucial attributes. There are no ready-made solutions for many tasks, therefore blockchain developers must frequently make their own selections. Because routine work and typical tasks are not common in this field, a good test activity for a future blockchain developer should include a challenge - the demand to go beyond the candidate's competencies.


It's worth noting that good coders have a good reputation. So, before you interview a candidate, check with his or her previous employment. Also, look over his or her past work portfolio to determine whether it's appropriate with the design of your project. A good developer should be familiar with current trends in the development of blockchain-based systems, necessary protocols, basic programming languages, digital currency fundamentals, tools, and software development processes.


Mutual psychological compatibility is one of the most significant criteria to consider when choosing a blockchain engineer. Quality contributors are vital in all aspects of company, but in the case of blockchain, their absence has a particularly significant impact on the outcomes. There are a variety of approaches to accomplishing this goal, including recruiting persons with similar backgrounds (i.e., from one university or community). Team building that is competent and careful takes into account the candidate's personal features as well as their psychological composition.


Blockchain Developers' Incentives

Currently, demand for vacancies in the blockchain industry vastly outnumbers supply. Candidates have a choice, and their motivation isn't solely based on a large salary. Intellectual and professional growth - active participation in the development of an industry and addressing intriguing and complicated issues – is one of the most effective motivators. The kind of incentives is also determined by the intellectual features of this business: alternatives, the opportunity of continual professional skill growth, participation in conferences and other worldwide events, and support for the initiative.


The ability to work remotely is a key factor for many developers when picking a company, but if you organise a suitable workspace, blockchain developers will be interested in working from the office. Bonuses like a gym, free lunches, and help with various concerns – in general, a high basic level of comfort that allows the team to focus on its immediate objectives – can persuade a candidate to take a job offer.


Personal goals, of course, are a winning alternative for attracting and maintaining valuable employees. It's extremely crucial for talented people (after all, you're looking for them) to be accepted for who they are. You will find loyal employees that are willing to work with your team for many years if you provide a personalised approach to each. The latter will be particularly useful. The blockchain craze isn't going away anytime soon, which means that good specialists will be in high demand in the next years.


Obtaining the Services of a Blockchain Developer

Many organisations and businesses (financial institutions and startups) are now looking at incorporating blockchain technology into their operations. Knowing how to get a true expert and experienced specialist to create a new system is therefore crucial to the project's success.


A good developer should be familiar with current trends in underlying technology, necessary protocols, basic programming languages, tools, and software development methodologies. The ideal candidate will have at least 3 years of development expertise in C/C++/Go/Rust/Java/Python/Ruby/C#/Solidity, and other programming languages.


This list is endless, so if you want to locate good specialists, you'll need to figure out what qualities and knowledge you need first, and then figure out what blockchain interview questions you'll need to ask.


We've compiled a list of the most important blockchain developer interview questions, cryptocurrency interview questions, and bitcoin interview questions to ask when hiring a decentralised network developer.


Questions for a Blockchain Interview

What exactly is blockchain, and why is it so revolutionary?


Blockchain is a brand-new, decentralised, secure, and transparent technology that enables the storing and exchange of data, as well as the verification of its authenticity, at a cheap cost. Because everything is done by the user in this technology, the transaction does not require the involvement of a third trustee. The main novelty and uniqueness of the distributed ledger is the lack of an intermediary. Digital currency, such as Bitcoin, Ethereum, Ripple, and other crypto assets or digital money, is the most well-known implementation of blockchain technology. This technique has a wide range of applications.


How can blockchain ensure transaction security and transparency?


Without a doubt, questions about transaction security and how it is achieved should be included in blockchain interview questions.


Technically, this is accomplished by encrypting data about each upcoming transaction in a sequential manner. Any transaction in a block is given a cryptographic identifier (hash) that is appended to the header of the following transaction's record, and this process is continued indefinitely so that the transaction hash at the chain's vertex contains encrypted data about all previous transactions. It is impossible to alter an already-recorded transaction because doing so would jeopardise the entire chain.




What types of blockchain are you familiar with?


There are three sorts of blockchains: public (available to all users), private (with limited access), and hybrid (a blend of the two previous types).


A private blockchain is a chain of blocks that can only be established by a small group of people with confirmed ownership rights. One or more people may own the rights (or one or several organizations). One or more nodes control the creation of new blocks in such a system.


On the other hand, anyone can establish a chain of blocks in the public blockchain (as in the mining of Bitcoins). It is accessible to all, and no one has authority over it.


Hybrid blockchain is a hybrid of the two preceding types of blockchain. It can be developed and used to make user interactions more secure, to guard against hacker attacks, and to protect against privacy invasion and external attacks.


What consensus algorithms are you familiar with?


This is one of the most critical blockchain interview questions. Consensus is a mathematical technique that ensures that all nodes in the blockchain network agree on the true and real state of the network, avoiding the possibility of digital currency double-spending. A number of consensus techniques exist to give protection:


  • Proof of Work: To confirm electronic transactions, users must run a hash algorithm numerous times or solve a mathematical puzzle using a specific technique. Bitcoins are circulated in the Bitcoin network by rewarding miners who successfully construct new blocks rewards.

  • Proof of Burn: This method is based on the notion of "burning" or "destroying" the coins owned by the miners who provide them mining rights.

  • Proof of Stake: If a user wishes to claim the confirmation of more blocks in the middle and be compensated for it, he or she must have some bitcoin.

  • Proof of Possession (Proof of Hold): The more money the user possesses, the more auditing privileges he or she gets.

  • Proof of Use: The more currency the user exchanges, the more rights he or she has to conduct an audit.

  • Users with the greatest confirmation rates in the cryptocurrency will be rewarded as proof of importance.

  • Delegated Proof of Stake (DPoS): Consensus selects a small set of people who can be trusted based on their reputation, which is gained by voting. Only these individuals have the authority to record blocks in a random order. All token owners have the ability to vote, and votes are weighted based on the number of coins a voter holds.


What is the blockchain and how does it work?


A registry (a row of blocks, for example, Bitcoin), encryption with keys to safeguard transactions, a consensus mechanism for confirming transactions, and a peer-to-peer network to make things function are all required to establish and work on the blockchain. When you include participants, you'll have all of the necessary elements.


When preparing for blockchain developer interview questions, keep in mind that there are a variety of duties to consider. You can test a candidate's technical abilities by asking him or her to build a rudimentary blockchain model.




What is the Merkle Tree, and how does it work?


The Merkle Tree (hash-tree) is a unique data structure that stores summary information about a huge quantity of data and is used to ensure data integrity. Here's a picture of a Merkle Tree:


Merkle Tree with Transactions in Java


What is the maximum number of parent blocks that a blockchain can have?


Due to the blockchain's structure, there is only one block.


In a blockchain, how are blocks connected?


Return to the previous block.


What is cryptography and how does it work? What is its primary objective?


Cryptography is a set of techniques for maintaining information's confidentiality and authenticity. It's the field of data encryption science. Cryptography's major goal is to safeguard data from tampering and unauthorised access while it is being stored and transferred from one sender to another.


The blockchain system must be constantly updated in order to function, adding records of new transactions to the network. The system is most vulnerable to attacks when it is being updated with new data. The legitimacy of all data and their security against unauthorised alterations are guaranteed thanks to a rigorous hierarchy in the block of chains.


The use of a hash function ensures that the current transaction chain is preserved. A new block refers to the preceding block's hash.



What is the purpose of the trapdoor?


The trapdoor function is a function that is simple to calculate one way but difficult to calculate the other. Asymmetric encryption systems (public key encryption) such as RSA make extensive use of trapdoor functions with secret input.


What exactly is RSA?


RSA is a public-key cryptography algorithm based on the computational complexity of the big integer factorization problem. The RSA cryptosystem was the first to work with both encryption and digital signatures.


What exactly is SHA-256?


The unidirectional hash functions SHA-224, SHA-256, SHA-384, and SHA-512 are together known as SHA-2 (Secure Hash Algorithm Version). Hash algorithms are used to create “prints” or “digests,” which are messages of any length. They're used in a variety of data-security-related programmes and components.





Your best candidate, of course, should have some experience with programming languages other than Java. C++ was used to construct Bitcoin, for example. The following is an example of a block in C++:



Here's how a SHA-256 hash is calculated in Go:





Here's an example of how to ensure proper blockchain performance:




Questions for a Bitcoin Interview


What exactly is Bitcoin?

Bitcoin is a decentralised, peer-to-peer payment system that operates without the use of a central authority (without a financial institution). This technology allows you to exchange tokens while also documenting each transaction (with automated date and time fixation) in a distributed ledger that cannot be changed.


The network supports transaction management and the generation of Bitcoin tokens collectively, and the architecture of this control is open; no one owns or manages a chain of Bitcoin blocks, and anyone can join it. The method provides for a variety of interesting uses that are not covered by modern payment systems due to several unique qualities.


What are the primary motivations for utilising the Bitcoin blockchain?


Don't forget to ask the candidate about the key benefits of bitcoin during the bitcoin interview questions. People use the Bitcoin network for a variety of reasons:


  • The biggest advantage of Bitcoin is that it is a simple and quick way to send money over the world.

  • A traditional bank transfer costs more than a transaction on the Bitcoin network;

  • Hackers can obtain your payment information from a regular payment system operator, but stealing Bitcoin payment addresses is pointless because a transaction is only legal if it is signed by a private key, which does not need to be sent anywhere in order to complete a transaction.




What is the Bitcoin blockchain and how does it work?

Bitcoin interview questions could also contain inquiries about how the currency works.


The formation and operation of the system is divided into four stages:

  • A transaction's terms are agreed upon by two parties (transfer of money, assets, financial documents, etc.)

  • Members of the network perform a "scan" of the registry. Members of the network ensure that the vendor has the assets that he or she sells by examining its chronology.

  • The transaction is confirmed and included to the chain's last block if the seller's data is correct.

  • All network members have access to the registry. Its widespread presence ensures its safety. To falsify the transaction, all members (nodes) of the network's logs would have to be changed.

Who are the Bitcoin system's participants?


Include some interview questions regarding the participants when preparing the bitcoin interview questions.


The Bitcoin system's participants are:


  • Users are the owners of an electronic wallet that can store cryptocurrency and send it to other users within the system.

  • Participants who process remunerative transactions made by users on the network and choose a hash for created blocks are known as miners.

  • Servers – participants who distribute the blockchain's general book and perform activities to verify that the blocks sent are compliant with the complexity and admissibility standards.

Questions to Ask in a Cryptocurrency Interview


What exactly is a cryptocurrency?

Cryptocurrencies are a type of electronic money whose operation is based on a decentralised process of emission and circulation. It is a complicated system of information and technological procedures that regulates the identification of owners and the reality of their change, and is based on cryptographic techniques of protection.


Asymmetric encryption and the use of various cryptographic methods of security are used to issue and account for cryptocurrency.


What exactly is Ethereum?

Ethereum is a must-know for all blockchain developers, therefore include it in your cryptocurrency interview questions. Ethereum is a decentralised platform for the execution of smart contracts. Smart contracts are programmable programmes that are free of censorship, fraud, and third-party interference. These applications are built on user blockchains and run on a global distributed infrastructure.



Ethereum contracts are based on an information technology protocol that allows for the verification or enforcement of a bilateral treaty. Within the blockchain, these contracts are unfoldable and open to public discussion.


One of the most popular platforms for developing blockchain apps is Ethereum.


What programming language is used to create smart contracts?


Every smart contract in Ethereum is written in the Solidity programming language, which is unique to Ethereum. Solidity is a complicated programming language with a JavaScript-like syntax. It was created to put together Ethereum virtual machine code. Solidity is a comprehensive Turing language that can be used to write both basic and complicated programmes.


What exactly is a fork?


Different users must employ basic regulatory rules to support blockchain record history, which is referred to as forks.


What is the difference between a hard fork and a soft fork? Do you have any experience with vulnerability instances involving hard/soft forks?


A hard fork in blockchain technology is a complete protocol mutation that allows previously invalid blocks/transactions to become valid (or vice-versa). For example, a recursive calling weakness allowed a hacker to break the code of the DAO smart contract in June 2016. To address the issue, Ethereum implemented a hard fork in July 2016, which involved altering the blockchain code in order to recover the DAO project's stolen funds and redistribute them to their rightful owners.


A soft fork, unlike a hard fork, is a change in the rules that results in blocks that are recognised as legitimate old software.


What exactly is a 51% attack?


When a single person or a group of people controls more than half of the processing power available for mining, a 51 percent attack is possible. He or she (they) have the ability to refuse or authorise transactions, as well as perform double costs. Indeed, the network's nodes (for example, the Bitcoin blockchain) consider the longest chain created by a group of miners with the most processing power as valid.


If such an assault were to occur, the network would almost certainly detect it immediately.


A Final Thought

Finding a skilled blockchain developer is difficult due to the newness and complexity of the digital currency technology. Interview questions on blockchain should bring up a slew of critical issues. And this is without considering the extensive discussion of its potential use cases or benefits, such as third-party refusal, transaction protection, resource sharing, economies of scale, transaction assurances, automatic contract execution, and process decentralisation.


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