CBSE - Certified Blockchain Security Expert Consensus Algorithm Security Questions and Answers

Question 1

A Proof-of-Stake blockchain is experiencing a chain fork.
A validator decides to validate transactions and create blocks on both forked chains simultaneously to maximize their potential rewards, regardless of which chain ultimately becomes canonical.
What specific security vulnerability does this action represent?

Accepted Answer

Nothing-at-Stake Problem

Answer

Selfish Mining

Answer

51% Attack

Answer

Eclipse Attack

Question 2

In a Proof-of-Work based cryptocurrency network, a mining pool has just acquired 52% of the total network hash rate. Which of the following malicious activities can this pool now successfully execute?

Accepted Answer

Reverse its own transactions that have already been confirmed.

Answer

Steal private keys from user wallets.

Answer

Change the fundamental consensus rules of the protocol.

Answer

Create new coins out of thin air, violating the supply limit.

Question 3

A private consortium blockchain uses the Practical Byzantine Fault Tolerance (PBFT) consensus algorithm. The network consists of 10 validator nodes. What is the maximum number of malicious or faulty nodes the network can withstand while still guaranteeing consensus?

Accepted Answer

3

Answer

1

Answer

5

Answer

4

Question 4

Which of the following consensus algorithms is most vulnerable to a Sybil attack where an attacker creates a large number of pseudonymous identities to gain disproportionate influence, assuming no significant economic barrier is in place?

Accepted Answer

A basic voting-based consensus without economic staking

Answer

Proof of Work (PoW)

Answer

Proof of Stake (PoS)

Answer

Practical Byzantine Fault Tolerance (PBFT) in a permissioned network

Question 5

A security analyst is reviewing a new public blockchain protocol. The protocol uses a Proof-of-Stake consensus mechanism where validators are penalized for downtime but not for signing conflicting blocks. The analyst flags a major security risk. What is the MOST likely risk they identified?

Accepted Answer

Long-Range Attack

Answer

Centralization of stake

Answer

Resource Exhaustion Attack

Answer

51% Attack

Question 6

An attacker plans to disrupt a Proof-of-Work blockchain by secretly mining a private chain that is longer than the public chain. The attacker includes a transaction sending funds to an exchange on the public chain, waits for the deposit to be confirmed, and then releases their longer private chain which does not contain this transaction, thereby invalidating it. This allows the attacker to keep their original funds. What is this attack called?

Accepted Answer

Selfish Mining

Answer

Timejacking Attack

Answer

Finney Attack

Answer

Race Attack