CBSA Smart Contract Design 2

Question 1

Which design pattern separates a smart contract's logic from its data storage to enable upgradability?

Accepted Answer

Proxy pattern

Answer

Factory pattern

Answer

Singleton pattern

Answer

Observer pattern

Question 2

What is a primary security risk of using 'tx.origin' for authorization in a Solidity smart contract?

Accepted Answer

It exposes the contract to phishing attacks via malicious intermediary contracts

Answer

It consumes significantly more gas than msg.sender

Answer

It is deprecated and no longer available in Solidity

Answer

It only works on private blockchain networks

Question 3

In smart contract design, what does the 'check-effects-interactions' pattern primarily prevent?

Accepted Answer

Reentrancy attacks

Answer

Integer overflow vulnerabilities

Answer

Front-running attacks

Answer

Gas limit exhaustion

Question 4

Which Ethereum opcode is used internally when a contract sends Ether using the 'transfer' function, and what is its gas stipend?

Accepted Answer

CALL with 2300 gas

Answer

SEND with 21000 gas

Answer

STATICCALL with 2300 gas

Answer

DELEGATECALL with 5000 gas

Question 5

What is the purpose of the 'circuit breaker' (emergency stop) pattern in smart contract design?

Accepted Answer

To pause contract functionality when a vulnerability is detected

Answer

To reduce gas costs during high network congestion

Answer

To automatically upgrade contract logic when a bug is found

Answer

To throttle the number of transactions per block

Question 6

When designing a smart contract that accepts ERC-20 token payments, why must you call 'approve' before 'transferFrom'?

Accepted Answer

Because transferFrom requires prior owner authorization via the allowance mechanism

Answer

Because approve permanently locks tokens in the contract

Answer

Because ERC-20 tokens cannot be transferred without minting new tokens first

Answer

Because the EVM requires two-step transactions for all token operations

Question 7

What is 'storage collision' in the context of upgradeable smart contracts using the proxy pattern?

Accepted Answer

When a proxy and its logic contract use the same storage slot for different variables

Answer

When two functions write to the same storage slot, corrupting data

Answer

When a contract runs out of available storage slots

Answer

When two contracts compete to write to the blockchain simultaneously