Blockchain Developer Security Principles 2

Question 1

A reentrancy attack on a smart contract is best mitigated by which design pattern?

Accepted Answer

Checks-effects-interactions pattern

Answer

Storing all state in memory

Answer

Using delegatecall for transfers

Answer

Increasing the gas limit

Question 2

Which Solidity construct provides reentrancy protection by locking a function during execution?

Accepted Answer

nonReentrant modifier with a mutex

Answer

pure modifier

Answer

view modifier

Answer

payable modifier

Question 3

Integer overflow vulnerabilities in older Solidity were commonly prevented using which library?

Accepted Answer

SafeMath

Answer

OpenZeppelin Ownable

Answer

Chainlink VRF

Answer

ERC20Detailed

Question 4

From Solidity 0.8.0 onward, how is integer overflow handled by default?

Accepted Answer

Arithmetic reverts automatically on overflow/underflow

Answer

Values silently wrap around

Answer

Compilation fails

Answer

Gas is refunded

Question 5

A front-running attack exploits which property of public blockchains?

Accepted Answer

Pending transactions are visible in the mempool before mining

Answer

Blocks are immutable once finalized

Answer

Private keys are reused

Answer

Gas prices are fixed

Question 6

Which technique helps protect against front-running by hiding transaction intent until confirmation?

Accepted Answer

Commit-reveal scheme

Answer

Increasing block size

Answer

Disabling events

Answer

Using tx.origin

Question 7

Why is using tx.origin for authorization considered insecure?

Accepted Answer

A malicious intermediary contract can trick the original user into authorizing it

Answer

It costs too much gas

Answer

It cannot be read in Solidity

Answer

It only works on testnets