Attack Surfaces in Blockchain Ecosystems BDC Practice Questions (Page 6)

Questions 26–30

1. 26expert · hard

   A proof-of-stake blockchain is considering a change to its consensus protocol to reduce the risk of long-range attacks. The network has a large number of validators and a long history. Which approach is most effective in mitigating long-range attacks?

   • ARequire validators to lock their tokens for a longer period to prevent them from selling and then attacking.
   • BUse a longer epoch length to make it harder for an attacker to accumulate enough blocks.
   • CImplement checkpointing, where finalized blocks are periodically recorded and cannot be reverted, preventing attackers from rewriting history from an early point.
   • DIncrease the block reward to incentivize validators to stay online and participate.
   Reveal Solution Discussion Select an answer first
2. 27application · medium

   A blockchain node operator notices that their node is only receiving blocks from a small set of peers, all of which are controlled by the same entity. The node's mempool is being filled with invalid transactions, and the node is unable to see the main chain. What type of attack is this?

   • ADDoS attack
   • BEclipse attack
   • CSelfish mining attack
   • DSybil attack
   Reveal Solution Discussion Select an answer first
4. 28foundation · easy

   What is a Sybil attack in a blockchain network?

   • AAn attacker isolates a specific node by surrounding it with malicious peers
   • BAn attacker creates many fake identities to gain disproportionate influence or control over the network
   • CAn attacker rewrites the blockchain history from a previous point
   • DAn attacker overwhelms the network with a flood of transactions
   Reveal Solution Discussion Select an answer first
5. 29application · easy

   A user stores their cryptocurrency private keys in a plain text file on their laptop. The laptop is infected with malware that logs keystrokes and takes screenshots. What is the most likely threat to the user's funds?

   • AThe malware can perform a 51% attack on the blockchain to steal the funds.
   • BThe malware can read the private key file directly and steal the funds.
   • CThe malware can launch an eclipse attack on the user's node to intercept transactions.
   • DThe malware can manipulate the user's governance votes to drain the DAO treasury.
   Reveal Solution Discussion Select an answer first
6. 30expert · hard

   A proof-of-work blockchain with a modest hash rate is experiencing a series of attacks. The attacker appears to be mining blocks but not broadcasting them immediately, then releasing them later to orphan honest blocks. The attacker also controls a large number of IP addresses to intercept and delay block propagation to specific miners. The network's governance is slow to respond because proposals require a high quorum. Which attack combination is the attacker MOST likely using?

   • AA long-range attack combined with a DDoS attack on the network's RPC endpoints.
   • BA governance attack combined with a phishing campaign against validators.
   • CA 51% attack combined with a Sybil attack to control the entire network.
   • DSelfish mining combined with an eclipse attack to isolate targeted miners.
   Reveal Solution Discussion Select an answer first