Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About LTIMindtree hiring for Blockchain roles
LTIMindtree is an Indian IT services and consulting company formed by the merger of Larsen and Toubro Infotech and Mindtree, and part of the L&T Group. It provides cloud, data, ERP, testing and digital engineering services for global clients. It hires for software engineers, test engineers, data analysts, data engineers and ERP consultants.
For Blockchain roles, this LTIMindtree practice set focuses most on Cryptography for Blockchain (5), Ethereum and the EVM (5), Solidity Programming (5), Consensus and Scaling (3). It has 15 easy, 15 medium questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Mumbai, India
Main India offices
Mumbai, Pune, Bengaluru, Chennai, Hyderabad
LTIMindtree Blockchain interview process
Online assessment (aptitude + reasoning)
Coding test
Technical interview
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
What are seed phrases and HD wallets (BIP-39, BIP-32, BIP-44)?
BIP-39 encodes random entropy as a 12 or 24 word mnemonic, which is turned into a binary seed. BIP-32 defines hierarchical deterministic wallets that derive a tree of key pairs from that seed. BIP-44 standardises the derivation path, for example m/44'/60'/0'/0/0 for the first Ethereum account. So one backed-up seed phrase can restore unlimited addresses across chains. Whoever knows the phrase controls every derived account, so it must never be stored online.
02
A user is angry that withdrawing from an optimistic rollup to Ethereum takes seven days. How do you explain and solve it?
Explain that the seven-day window lets anyone challenge a fraudulent batch; it protects their funds. For faster exits, offer third-party fast bridges or intent-based bridges where a liquidity provider pays them on L1 within minutes for a small fee and later claims the slow withdrawal. Also show the expected timeline clearly in the UI and send a notification when funds are claimable, because most anger comes from uncertainty, not the delay itself.
03
How do you approve and transfer ERC-20 tokens from a script with ethers.js?
Use cast storage with the contract address and slot number. For mappings, compute the slot as keccak256(key . slot).
# Read slot 0 (often the first state variable)
cast storage 0xContractAddress 0 --rpc-url $RPC_URL
# balanceOf mapping stored at slot 2, key = user address
cast index address 0xUserAddress 2
cast storage 0xContractAddress <slot-from-above> --rpc-url $RPC_URL
This shows that private variables are not secret: anyone can read storage.
06
What is the difference between SHA-256 and Keccak-256?
SHA-256 is from the SHA-2 family and uses a Merkle-Damgard construction; Bitcoin uses double SHA-256 for block hashes and transaction IDs. Keccak-256 is based on the sponge construction and is what Ethereum uses for addresses, function selectors, event topics and storage slots. Ethereum's Keccak-256 is the original Keccak submission and differs from the final NIST SHA3-256 in padding, so the two give different outputs for the same input.
07
What is the difference between receive and fallback functions?
receive() external payable runs when a contract receives plain ETH with empty calldata, for example a transfer from a wallet. fallback() runs when calldata matches no function, or when ETH arrives with data and no receive exists; it must be payable to accept ETH. Proxies use fallback to delegatecall all unknown calls to the implementation. Keep both simple, since a reverting or gas-heavy receive can break senders that use transfer with its 2300 gas stipend.
08
How are mappings stored, and why can you not iterate over them?
A mapping does not store keys. The value for key k in a mapping declared at slot p lives at storage slot keccak256(k . p). Every possible key implicitly exists with a default zero value, so the contract cannot know which keys were set or how many. To iterate, keep a separate array of keys or use OpenZeppelin EnumerableSet or EnumerableMap, accepting extra gas, or rebuild the list off-chain from emitted events.
09
What is double spending and how does a blockchain prevent it?
Double spending is trying to spend the same digital money twice, for example sending the same coins to two merchants. A blockchain prevents it by keeping one shared ordering of transactions agreed through consensus. Once a transaction is included in a block, any conflicting transaction that spends the same funds is rejected as invalid. Merchants wait for several confirmations so that the chance of the block being replaced in a reorg becomes negligible.
Inherit the audited ERC20 implementation and mint the initial supply in the constructor.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;
import {ERC20} from '@openzeppelin/contracts/token/ERC20/ERC20.sol';
import {Ownable} from '@openzeppelin/contracts/access/Ownable.sol';
contract CampusToken is ERC20, Ownable {
constructor() ERC20('Campus Token', 'CAMP') Ownable(msg.sender) {
_mint(msg.sender, 1_000_000 * 10 ** decimals());
}
function mint(address to, uint256 amount) external onlyOwner {
_mint(to, amount);
}
}
A revert undoes all state changes made during that transaction, including nested calls, as if it never ran. However, the transaction is still included in a block, the nonce is consumed, and the sender pays for the gas used up to the revert. Contracts revert with require, revert or custom errors, which return a reason the wallet can show. Since the Byzantium upgrade, unused gas is refunded on revert, unlike the old invalid opcode which consumed everything.
12
What is the difference between view, pure and payable functions?
A view function reads state but does not modify it, so it is free when called off-chain via eth_call. A pure function neither reads nor modifies state and works only on its inputs, for example a math helper. A payable function can receive ETH along with the call; non-payable functions revert if ETH is sent. View and pure functions still cost gas when called inside a state-changing transaction.
ERC-20 defines fungible tokens where every unit is identical, with functions like transfer, approve, transferFrom and balanceOf; used for currencies, stablecoins and governance tokens. ERC-721 defines non-fungible tokens where each tokenId is unique, used for NFTs like art, tickets or certificates. ERC-1155 is a multi-token standard where one contract manages many token types, fungible or not, with batch transfers; it is popular in games where items have quantities.
14
Why should you check return values of low-level calls and use SafeERC20?
Low-level call, send and delegatecall return false instead of reverting on failure, so ignoring the result means the contract continues as if the transfer succeeded. Similarly, some ERC-20 tokens do not return a bool from transfer, and others return false instead of reverting. OpenZeppelin's SafeERC20 wraps transfer, transferFrom and approve to handle both cases and revert on failure. Always write (bool ok, ) = to.call{value: x}(''); require(ok).
Fiat-backed stablecoins hold cash and short-term government bonds off-chain, one dollar per token, and depend on the issuer's audits and redemptions. Crypto-collateralised stablecoins are minted against overcollateralised crypto in smart contracts, such as vaults requiring 150 percent collateral. Algorithmic stablecoins try to hold the peg with supply rules and incentives; several have collapsed, the most famous in 2022. Choose based on trust model, liquidity, transparency and regulatory status.
16
How is public-key cryptography used in blockchain?
Each user has a private key, kept secret, and a public key derived from it. The private key signs transactions, and anyone can verify the signature with the public key, proving the owner authorised the transfer without revealing the private key. Addresses are derived from public keys. Because control of funds equals control of the private key, losing it means losing access, and leaking it means anyone can spend the funds.
In Proof of Work, miners repeatedly change a nonce and hash the block header until the hash is below a difficulty target. Finding it takes huge computation, but anyone can verify it with one hash. The first miner to succeed broadcasts the block and earns the block reward plus fees. Nodes follow the chain with the most accumulated work. Bitcoin targets a block every ten minutes and adjusts difficulty every 2016 blocks to keep that pace.
18
An HR team wants to store employee records on a blockchain. Would you recommend it?
Usually no. Employee records are owned by one organisation, change often and contain personal data that must be correctable and deletable under the DPDP Act 2023. A normal database with role-based access and audit logs is cheaper, faster and compliant. I would ask who else needs to trust the data. If several employers or background-check agencies must verify certificates, I would store only hashes of credentials on a permissioned chain and keep the actual data off-chain.
19
What is a digital signature and what does it guarantee?
A digital signature is a value produced by signing a message hash with a private key. Anyone with the public key can verify it. It guarantees authentication (the holder of the key signed it), integrity (the message was not changed, since any change breaks verification) and non-repudiation (the signer cannot later deny it). In blockchain, every transaction is signed, so nodes accept a transfer only if the signature matches the sending account.
20
Which tools do you use for static analysis and fuzzing of smart contracts?
Slither performs static analysis and quickly flags reentrancy, unchecked calls, shadowing and more. Aderyn is another fast static analyser. Foundry provides fuzz and invariant testing, where random sequences of calls try to break properties you define. Echidna and Medusa are property-based fuzzers. Mythril and Halmos use symbolic execution, and Certora offers formal verification. Combining them with manual review and high test coverage catches far more than any single tool.
IPFS, the InterPlanetary File System, is a peer-to-peer network for storing and sharing files. Instead of locating files by server address, it identifies them by a content identifier (CID) derived from the file's hash, which is content addressing. The same content always has the same CID, and any change gives a new CID, so data cannot be swapped silently. Files must be pinned by a node or pinning service, otherwise they may disappear.
22
Explain public, external, internal and private visibility.
public functions can be called externally and internally, and public state variables get an automatic getter. external functions can only be called from outside, or via this.f(), and read arguments directly from calldata. internal functions and variables are available to the contract and contracts that inherit it. private is limited to the defining contract only. Note that private only restricts other contracts; the data is still fully visible on the blockchain to anyone.
23
After a transaction is confirmed, your front-end still shows old data. How do you fix it?
The UI is probably reading cached results or a lagging RPC node. After tx.wait() resolves, explicitly refetch or invalidate the relevant queries, for example with wagmi or TanStack Query invalidation. Show optimistic updates while pending. If you use an indexer, it may lag by a few blocks, so poll until it reaches the receipt's block number. Use the same RPC endpoint for writes and immediate reads, and avoid long caching for balances.
24
How did integer overflow bugs happen before Solidity 0.8?
Before 0.8, arithmetic wrapped silently: a uint8 at 255 plus 1 became 0, and 0 minus 1 became the maximum value. Attackers exploited this, for example by making a balance underflow to a huge number or an overflowed multiplication pass a check, as in the 2018 batchOverflow token bug. Developers used the SafeMath library to revert on overflow. Since 0.8 the compiler checks automatically, except inside unchecked blocks and in inline assembly.
Events are declared in Solidity and emitted with emit; the EVM writes them as logs in the transaction receipt. Each log has the contract address, up to three indexed topics plus the event signature hash, and non-indexed data. Logs are much cheaper than storage but contracts cannot read them. Front-ends and indexers subscribe to events to update the UI, track token transfers and build history, so emitting clear events for every state change is good practice.
26
What is Bitcoin halving and difficulty adjustment?
Halving cuts the Bitcoin block reward in half every 210,000 blocks, roughly every four years, which caps total supply at 21 million BTC. After the April 2024 halving the reward is 3.125 BTC per block. Difficulty adjustment happens every 2016 blocks: if blocks came faster than ten minutes on average, difficulty rises, and if slower, it falls. Together they make issuance predictable regardless of how much mining power joins or leaves.
The mempool is each node's waiting area for valid transactions that have been broadcast but not yet included in a block. Block producers usually pick transactions paying the highest fees or priority tips. Every node has its own mempool, so contents can differ slightly. Because pending transactions are public, bots can watch the mempool and front-run trades, which is why private transaction relays and order-flow auctions are used for sensitive transactions.
Gas measures the computational work an operation needs; for example a simple ETH transfer uses 21,000 gas, and writing a new storage slot costs about 20,000. The gas limit is the maximum gas the sender allows a transaction to consume. The gas price, per unit, is what the sender pays. The fee equals gas used times the effective gas price. If execution exceeds the limit, it reverts but the used gas is still charged.
Testnets are public networks that run the same software as mainnet but with valueless ETH, so developers can test deployments and dApps safely. Sepolia is the main testnet for application developers, and Hoodi replaced Holesky for validator and staking testing in 2025. Test ETH comes from faucets, which often require a small mainnet balance or a login to stop abuse. Many Layer 2s run their own Sepolia-based testnets bridged from Ethereum Sepolia.
30
Describe a time you found a security problem in code and how you handled it.
Situation: while reviewing a teammate's staking contract, I saw it sent tokens before updating the user's balance. Task: confirm the risk without blaming anyone. Action: I wrote a Foundry test with a malicious receiver that re-entered withdraw and drained extra funds, then shared it privately with a suggested fix using checks-effects-interactions and a reentrancy guard. Result: the fix merged before the audit, and we added reentrancy tests to our standard checklist.
Tips to crack the LTIMindtree Blockchain interview
Practise aptitude, logical reasoning and basic coding questions, as the online assessment is usually the first filter.
Revise SQL, OOP and testing fundamentals, plus any cloud or data tools you list on your resume.
Learn about the L&T Group background and the LTI and Mindtree merger to answer company-related questions.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; LTIMindtree interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the LTIMindtree Blockchain interview?
Candidates usually go through 4 stages: Online assessment (aptitude + reasoning); Coding test; Technical interview; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the LTIMindtree Blockchain interview?
This practice set leans on Cryptography for Blockchain (5), Ethereum and the EVM (5), Solidity Programming (5), Consensus and Scaling (3). Revise those first, then practise explaining one or two of your own projects end to end, because most LTIMindtree interviewers ask you to walk through real work.
Are these the exact questions asked at LTIMindtree?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like LTIMindtree's. They are not a leaked or verified list of past questions.
Where does LTIMindtree hire Blockchain professionals in India?
LTIMindtree has large teams in Mumbai, Pune, Bengaluru, Chennai, Hyderabad. Openings and locations change often, so check the LTIMindtree careers page and filter by city and experience.