Ethereum Smart Contracts BBLC Practice Questions (Page 4)

Questions 16–20

1. 16expert · hard

   A smart contract uses tx.origin for authorization in a critical function. An auditor flags this as a security risk. Which attack is the auditor most likely concerned about?

   • ADenial-of-service attacks that prevent the contract from being called.
   • BOverflow attacks that cause the authorization check to be bypassed.
   • CPhishing attacks where a malicious contract tricks a user into calling it, and the malicious contract then calls the vulnerable contract using the user's credentials.
   • DReentrancy attacks where the contract is called recursively.
   Reveal Solution Discussion Select an answer first
2. 17application · medium

   A user is about to call a function on a deployed smart contract that updates a large array in storage. The user wants to estimate the gas cost before submitting the transaction. Which tool or method should they use?

   • AUse the contract's ABI to calculate the gas based on the function signature.
   • BUse eth_estimateGas RPC method to simulate the call and get an estimate.
   • CSubmit the transaction with a very high gas limit and see what is refunded.
   • DCheck the gas price from a gas oracle and multiply by the number of array elements.
   Reveal Solution Discussion Select an answer first
4. 18expert · hard

   A smart contract for a lottery uses a uint8 variable to track the total number of tickets sold. The contract increments this variable each time a ticket is purchased. After the contract has been live for a while, users report that ticket purchases are failing. What is the most likely cause?

   • AThe contract's owner has called selfdestruct.
   • BThe uint8 variable has overflowed, causing the transaction to revert.
   • CThe contract has run out of gas because of too many tickets.
   • DThe network is congested, so all transactions are failing.
   Reveal Solution Discussion Select an answer first
5. 19application · medium

   A developer is about to deploy a smart contract to the Ethereum mainnet. They want to verify the bytecode that will be executed. Which step should they take before deployment?

   • ARun the contract on a local testnet and check the transaction receipts.
   • BCompile the Solidity source code with the same compiler version and settings, then compare the resulting bytecode to the deployed bytecode.
   • CAsk a colleague to review the source code manually.
   • DUse a decompiler to reverse-engineer the bytecode and check for vulnerabilities.
   Reveal Solution Discussion Select an answer first
6. 20application · medium

   A group of investors wants to create a decentralized fund where members can vote on investment proposals and automatically distribute profits. Which smart contract use case is most appropriate?

   • AA token issuance contract that creates a new token for each investment.
   • BA decentralized exchange contract that allows trading of investment tokens.
   • CA decentralized autonomous organization (DAO) contract that manages voting and treasury.
   • DA supply chain contract that tracks the movement of funds.
   Reveal Solution Discussion Select an answer first