Certified Blockchain Professional (CBCP) MCQ Flashcards

Which consensus mechanism requires validators to lock up cryptocurrency as collateral to participate in block creation?

Answer: Proof of Stake

Proof of Stake requires validators to stake (lock) cryptocurrency as collateral, with the probability of creating the next block proportional to the amount staked.

In Ethereum's EVM, what is the purpose of 'gas' in transaction processing?

Answer: It measures computational effort and prevents infinite loops

Gas measures the computational effort required to execute operations on the EVM, prevents infinite loops by limiting execution, and compensates miners/validators for processing.

What distinguishes a 'hard fork' from a 'soft fork' in blockchain protocol upgrades?

Answer: Hard forks are backward-incompatible while soft forks maintain backward compatibility

A hard fork creates a permanent divergence by introducing rules that old nodes cannot validate, making it backward-incompatible, whereas a soft fork tightens rules that old nodes can still accept.

Which data structure does Bitcoin use to efficiently prove that a specific transaction is included in a block?

Answer: Merkle Tree

Bitcoin uses a Merkle Tree to organize transactions in a block, allowing lightweight clients to verify transaction inclusion with a Merkle proof without downloading the full block.

In a Hyperledger Fabric network, what role does the 'Orderer' node serve?

Answer: It establishes transaction order and creates blocks for distribution

The Orderer in Hyperledger Fabric collects endorsed transactions, establishes a consistent ordering, packages them into blocks, and distributes those blocks to peer nodes.

What is the primary security property provided by digital signatures in blockchain transactions?

Answer: Non-repudiation — the sender cannot deny authorizing the transaction

Digital signatures provide non-repudiation by cryptographically proving that only the private key holder could have authorized the transaction, preventing later denial.

Which attack vector exploits a smart contract that calls an external contract before updating its own state?

Answer: Reentrancy Attack

A reentrancy attack occurs when a malicious contract repeatedly re-enters the vulnerable contract's function before the original call updates its balance or state, draining funds.