Blockchain Technology Smart Contracts and dApps 2

Question 1

Which vulnerability allowed the 2016 DAO hack, draining ~$60M worth of ETH?

Accepted Answer

Reentrancy attack

Answer

The DAO hack exploited a reentrancy vulnerability where the attacker's fallback function recursively called withdraw() before the balance was updated.

Question 2

What does the 'payable' keyword do in a Solidity function?

Accepted Answer

Enables the function to receive Ether

Answer

The 'payable' modifier allows a Solidity function to receive Ether; without it, any ETH sent to the function will be rejected.

Question 3

In Ethereum, what is the purpose of the ABI (Application Binary Interface)?

Accepted Answer

To define how to encode and decode function calls and data

Answer

The ABI defines the encoding scheme for function signatures and parameters, allowing external callers to interact with a deployed smart contract.

Question 4

Which dApp architecture pattern uses IPFS or Arweave for storing large data off-chain?

Accepted Answer

Hybrid storage pattern

Answer

The hybrid storage pattern stores large or mutable data on decentralized file systems (IPFS/Arweave) while anchoring only content hashes on-chain.

Question 5

What is a 'view' function in Solidity?

Accepted Answer

A function that reads state but does not modify it

Answer

A 'view' function promises not to modify state, so it can be called without a transaction and without spending gas (when called externally).

Blockchain Practice Test

Blockchain Practice Test

Blockchain Technology Smart Contracts and dApps 2