CBSE Node and Network Security 3

Question 1

A blockchain validator node is targeted by an attacker who controls 51% of peers and delays block propagation to all other honest nodes. What is this strategy called?

Accepted Answer

Network partitioning with block withholding

Answer

By partitioning the honest network and withholding new blocks, the attacker can force honest miners onto a stale chain while the attacker's chain grows ahead.

Question 2

Which firewall rule set best protects a Bitcoin full node while still allowing legitimate peer-to-peer traffic on mainnet?

Accepted Answer

Allow inbound TCP 8333, block all other inbound; allow all outbound

Answer

Bitcoin P2P runs on TCP 8333; restricting other inbound ports limits attack surface while allowing peers to connect, and blocking RPC port 8332 from inbound prevents remote RPC abuse.

Question 3

What does 'transaction malleability' allow an attacker to do at the network level before a transaction is confirmed?

Accepted Answer

Alter the transaction ID (txid) by modifying the scriptSig without changing its validity

Answer

Transaction malleability lets a third party tweak the scriptSig data, producing a different txid for the same economic transaction, which can confuse tracking systems.

Question 4

A node operator wants to mitigate Sybil attacks in their private blockchain network. Which identity mechanism provides the strongest resistance?

Accepted Answer

Permissioned membership with certificate-based node identity (e.g., X.509 via a CA)

Answer

Certificate-based identity ties each node to a CA-issued credential, making it expensive for an attacker to create unlimited fake identities.

Question 5

Which metric in node monitoring most directly indicates an ongoing eclipse attack against a blockchain node?

Accepted Answer

All peer connections resolving to the same ASN or IP subnet

Answer

Eclipse attacks rely on filling the victim's peer table with attacker-controlled nodes, so seeing all peers from a single ASN or narrow IP range is a strong indicator.

(CBSE) Certified Blockchain Security Expert Practice Test

(CBSE) Certified Blockchain Security Expert Practice Test

CBSE Node and Network Security 3