FREE Blockchain Security Training Blockchain Network-Level Attacks Questions and Answers

Question 1

An attacker targets a specific mining node by gaining control of its router. They ensure all of the node's outgoing peer connections are exclusively established with malicious nodes controlled by the attacker. The victim's node continues to operate but only sees a fraudulent version of the blockchain. What type of network-level attack is this?

Accepted Answer

Eclipse Attack

Answer

An Eclipse attack isolates a specific node from the legitimate network by controlling all of its peer connections. This allows the attacker to filter the node's view of the blockchain, potentially leading to double-spending or selfish mining attacks against that specific victim.

Question 2

Which of the following best describes how a BGP (Border Gateway Protocol) hijacking attack can be used to disrupt a blockchain network?

Accepted Answer

By maliciously re-routing internet traffic intended for major nodes or mining pools to a location controlled by the attacker.

Answer

BGP hijacking is a routing attack where an attacker falsely advertises ownership of IP prefixes they do not control. This can redirect internet traffic, allowing the attacker to intercept or blackhole data intended for key blockchain participants like large mining pools, effectively partitioning them from the network.

Question 3

A network attacker successfully manipulates the Network Time Protocol (NTP) responses received by a blockchain node, causing its system clock to be significantly skewed. The node begins rejecting new, valid blocks because their timestamps appear to be too far in the future according to its incorrect local time. This attack is known as:

Accepted Answer

Timejacking

Answer

Timejacking involves manipulating a node's perception of time, typically by attacking its time source (like NTP). By skewing the node's clock, an attacker can cause it to reject valid blocks or accept invalid ones by exploiting the timestamp rules within a blockchain's protocol.

Question 4

A large, public blockchain network experiences a sudden degradation in performance. Investigation reveals that a significant number of publicly accessible full nodes are being flooded with an overwhelming volume of garbage P2P messages and transaction requests, consuming their bandwidth and CPU. This prevents them from relaying valid transactions and blocks. What is the most likely network-level attack occurring?

Accepted Answer

Distributed Denial-of-Service (DDoS) Attack

Answer

A Distributed Denial-of-Service (DDoS) attack aims to make a network resource unavailable. In this scenario, attackers are overwhelming the blockchain nodes with junk traffic, consuming their resources (CPU, bandwidth) and preventing them from performing their essential functions of validating and propagating legitimate network data.

Question 5

Which of the following accurately describes a transaction malleability attack at the network level?

Accepted Answer

An attacker modifies the digital signature of a valid, unconfirmed transaction in a way that changes the transaction ID (TXID) but not the fundamental validity of the transfer.

Answer

Transaction malleability exploits the fact that in some protocols, a transaction's signature can be altered without invalidating it. This alteration, however, changes the transaction's unique ID (TXID). An attacker can use this to cause confusion, for example, making it appear as though a payment was never confirmed by referencing the original TXID.

Blockchain Practice Test

Blockchain Practice Test

FREE Blockchain Security Training Blockchain Network-Level Attacks Questions and Answers