CBSA - Certified Blockchain Solution Architect Smart Contract Design Questions and Answers

Question 1

A development team is building a decentralized application (dApp) that will require periodic updates to its business logic after deployment. Which smart contract design pattern is most appropriate to allow for these updates without requiring users to migrate to a new contract address?

Accepted Answer

The Proxy Pattern

Answer

The Proxy Pattern is the most suitable choice for enabling smart contract upgrades. This pattern separates the contract's state and logic into two different contracts. The proxy contract holds the state and the public address that users interact with, while the logic contract contains the business logic. Calls are delegated from the proxy to the logic contract. To upgrade, a new logic contract is deployed, and the proxy is updated to point to the new logic contract's address, preserving the state and contract address.

Question 2

As a Blockchain Solution Architect, you are reviewing a smart contract designed for a decentralized finance (DeFi) lending protocol. You identify a function that sends funds to an external address before updating the internal state of the contract. Which of the following vulnerabilities is this design susceptible to?

Accepted Answer

Reentrancy Attack

Answer

This design is vulnerable to a reentrancy attack. An attacker could create a malicious contract that, upon receiving funds, calls back into the original function before the state (e.g., the user's balance) is updated. This would allow the attacker to withdraw funds multiple times. The best practice to prevent this is the Checks-Effects-Interactions pattern, where all internal state changes are made before any external calls.

Question 3

Which of the following is a primary benefit of designing smart contracts with a modular approach, breaking down complex logic into smaller, interconnected contracts or libraries?

Accepted Answer

It enhances code reusability, maintainability, and security.

Answer

A modular design improves code reusability, as common functions can be placed in libraries. It also enhances maintainability and testability by isolating specific functionalities. This separation of concerns can lead to better security, as it's easier to audit and reason about smaller, focused pieces of code.

Question 4

A team is designing a smart contract system where different user roles (e.g., admin, user, auditor) must have different permissions to execute certain functions. Which design pattern is most critical to implement for this requirement?

Accepted Answer

Access Control Pattern

Answer

The Access Control Pattern is essential for managing permissions within a smart contract. It involves implementing mechanisms, such as function modifiers (e.g., `onlyOwner`), to restrict access to sensitive functions based on the caller's address or role. This prevents unauthorized users from executing critical operations.

Question 5

In the context of smart contract design, what is the primary purpose of the 'Checks-Effects-Interactions' pattern?

Accepted Answer

To prevent reentrancy attacks by performing state changes before external calls.

Answer

The 'Checks-Effects-Interactions' pattern is a security best practice designed to mitigate reentrancy vulnerabilities. It dictates that a function should first perform all necessary checks (e.g., `require` statements), then apply all effects to the contract's state (e.g., updating balances), and only then interact with external contracts or addresses. This ensures the internal state is consistent before any external code is executed.

(CBSA) Certified Blockchain Solution Architect Practice Test

(CBSA) Certified Blockchain Solution Architect Practice Test

CBSA - Certified Blockchain Solution Architect Smart Contract Design Questions and Answers