Smart Contract Design Flashcards

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

Answer: Proxy pattern

The proxy pattern delegates calls to a logic contract while keeping state in a separate storage contract, allowing logic upgrades without migrating data.

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

Answer: It exposes the contract to phishing attacks via malicious intermediary contracts

A malicious contract can trick the original sender into calling it, and tx.origin still returns that user's address, bypassing intended authorization checks.

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

Answer: Reentrancy attacks

By updating internal state (effects) before calling external contracts (interactions), the pattern prevents reentrant calls from exploiting stale state.

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

Answer: CALL with 2300 gas

The 'transfer' function uses the CALL opcode but forwards only 2300 gas, which is enough for a log event but prevents most reentrancy.

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

Answer: To pause contract functionality when a vulnerability is detected

A circuit breaker allows an authorized admin to halt critical functions so funds can be protected while a vulnerability is investigated and fixed.

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

Answer: Because transferFrom requires prior owner authorization via the allowance mechanism

The ERC-20 allowance mechanism requires the token owner to first approve a spender's address for a specific amount before transferFrom can pull those tokens.

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

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

If a proxy contract's admin variable occupies the same storage slot as a variable in the logic contract, one will overwrite the other causing data corruption.