Blockchain Security and Attacks Questions and Answers

Question 1

An attacker creates thousands of pseudonymous nodes on a peer-to-peer blockchain network.
The goal is to gain a disproportionately large influence, potentially overpowering honest nodes in consensus or disrupting network routing.
What is this type of attack called?

Accepted Answer

Sybil Attack

Answer

Eclipse Attack

Answer

Dusting Attack

Answer

51% Attack

Question 2

A smart contract function is designed to transfer a user's remaining token balance. The code is written as `balances[user] -= amount;`. If a user with a balance of 100 tokens calls this function with an `amount` of 101, and the contract is running on an older, unprotected version of Solidity, the user's balance could wrap around to a very large number. This vulnerability is known as:

Accepted Answer

Integer Underflow

Answer

Reentrancy

Answer

Oracle Manipulation

Answer

Timestamp Dependence

Question 3

A user notices they have received several unsolicited transactions, each for a minuscule amount of cryptocurrency (e.g., 0.00000546 BTC), in their wallet. What is the most likely purpose of this 'dusting attack'?

Accepted Answer

To de-anonymize the wallet owner by tracking how and when this 'dust' is spent with other funds.

Answer

To clog the network with spam transactions, increasing fees for everyone.

Answer

To test if the user's wallet address is active before sending a larger, legitimate payment.

Answer

To advertise a new coin or project by sending small amounts to active wallets.

Question 4

A malicious miner on a Proof-of-Work blockchain successfully mines a block but chooses not to broadcast it to the network. Instead, they immediately start mining the next block on top of their secret one. The goal is to build a longer private chain and release it strategically to orphan blocks found by honest miners. This strategy is known as:

Accepted Answer

Selfish Mining

Answer

Block Withholding

Answer

Time-jacking Attack

Answer

Finney Attack

Question 5

An attacker wants to isolate a single, specific node from the rest of the blockchain network. They do this by monopolizing all of the target node's incoming and outgoing peer connections with nodes they control. This allows the attacker to feed the victim false transaction data and a counterfeit view of the blockchain. Which network-level attack is being described?

Accepted Answer

Eclipse Attack

Answer

Sybil Attack

Answer

Forking Attack

Answer

Denial-of-Service Attack

Question 6

A user stores their cryptocurrency private key in a plain text file named `wallet_key.txt` in a public GitHub repository. What is the most immediate and severe consequence of this action?

Accepted Answer

The user's funds can be immediately and irreversibly stolen by anyone who finds the key.

Answer

The network will automatically freeze the funds associated with the key for security reasons.

Answer

An attacker can view the transaction history but cannot initiate new transactions.

Answer

The user will receive a warning from GitHub to remove the sensitive information.