CBE - Certified Blockchain Expert Smart Contracts and DApps Questions and Answers

Question 1

A development team is building a decentralized application (DApp) for supply chain management. The DApp needs to automatically trigger a payment to a supplier once a shipment's arrival is confirmed by an external logistics provider's API. What component is essential for the smart contract to securely interact with this off-chain data?

Accepted Answer

A blockchain oracle.

Answer

Smart contracts on a blockchain cannot directly access real-world, off-chain data. A blockchain oracle is a service that acts as a bridge, fetching and verifying external information (like an API response) and feeding it to the smart contract to trigger its execution.

Question 2

Which of the following is a primary characteristic that distinguishes a smart contract from a traditional legal contract?

Accepted Answer

Its terms are self-executing and enforced by code on a blockchain.

Answer

The core difference is that a smart contract is a self-executing agreement with the terms of the agreement directly written into lines of code. It automatically enforces the rules and obligations defined within it when predetermined conditions are met, without the need for a traditional intermediary or legal system.

Question 3

A developer is writing a Solidity smart contract that handles user withdrawals. They write the code to send the Ether to the user's address *before* updating the user's balance in the contract's state. This sequence of operations makes the contract vulnerable to which specific type of attack?

Accepted Answer

Reentrancy

Answer

A reentrancy attack occurs when an external call is made to another contract before the original function has finished its execution, particularly before updating its state. A malicious contract can exploit this by repeatedly calling the withdraw function, re-entering the code before the balance is updated, and draining funds.

Question 4

What is the fundamental role of the backend in a typical Decentralized Application (DApp) architecture?

Accepted Answer

To run on a decentralized peer-to-peer network, typically consisting of smart contracts.

Answer

The defining characteristic of a DApp is that its backend logic runs on a decentralized network, not a central server. This backend is primarily composed of smart contracts that execute on the blockchain, ensuring the application is censorship-resistant and operates in a trustless manner.

Question 5

A financial DApp allows users to lend and borrow assets. The interest rates for these loans must be adjusted based on real-world market data. Which of the following is NOT a primary component needed to build this DApp?

Accepted Answer

A centralized server to store all transaction history for faster queries.

Answer

A core principle of a DApp is decentralization. While some off-chain storage might be used, storing all transaction history on a centralized server would create a single point of failure and defeat the purpose of using a blockchain. The transaction history is immutably stored on the blockchain itself.

CBE - Certified Blockchain Expert Practice Test

CBE - Certified Blockchain Expert Practice Test

CBE - Certified Blockchain Expert Smart Contracts and DApps Questions and Answers