CBCP Blockchain Fundamental 4 — Questions and Answers
Question 1: In blockchain, what is a 'mempool' (memory pool)?
- A temporary off-chain database for archiving old blocks
- A holding area where unconfirmed transactions wait to be included in a block (Correct answer)
- A RAM-based cache that stores the current blockchain state
- A pool of mining hardware shared across a network
Correct answer: A holding area where unconfirmed transactions wait to be included in a block
The mempool is each node's local buffer of broadcast transactions awaiting confirmation; miners select transactions from it to fill new blocks.
Question 2: What property ensures that a blockchain transaction cannot be denied or reversed by the sender after it is confirmed?
- Confidentiality
- Non-repudiation (Correct answer)
- Availability
- Scalability
Correct answer: Non-repudiation
Non-repudiation, enforced by digital signatures and immutable ledger records, means a sender cannot later claim they did not authorize a transaction.
Question 3: What is a '51% attack' and why does it threaten blockchain security?
- A spam attack sending 51 million transactions per second to overload the network
- When a single entity controls more than half of the network's consensus power, enabling double-spends (Correct answer)
- A vulnerability where 51% of smart contract code is flawed
- A scenario where 51 nodes simultaneously go offline
Correct answer: When a single entity controls more than half of the network's consensus power, enabling double-spends
Controlling >50% of hash rate (PoW) or stake (PoS) lets an attacker rewrite recent history and double-spend coins on that chain.
Question 4: Which component of asymmetric cryptography is used to verify a blockchain transaction's digital signature?
- The sender's private key
- The sender's public key (Correct answer)
- The network's shared symmetric key
- The block's Merkle root
Correct answer: The sender's public key
Anyone can use the sender's public key to verify that the signature was created by the corresponding private key, confirming authenticity without exposing the private key.
Question 5: What does 'finality' mean in the context of blockchain consensus?
- The process of archiving old blocks to reduce storage
- The guarantee that a confirmed transaction cannot be reversed (Correct answer)
- The moment a miner receives their block reward
- The maximum number of transactions a block can contain
Correct answer: The guarantee that a confirmed transaction cannot be reversed
Finality describes the point at which a transaction is considered irreversibly settled; different consensus mechanisms offer probabilistic or absolute finality.
Question 6: In blockchain architecture, what is the purpose of a 'sidechain'?
- To replace the main blockchain when it becomes congested
- To run transactions off the main chain while remaining pegged to it, enabling scalability and experimentation (Correct answer)
- To store private keys for all network validators
- To serve as an archive for blocks older than one year
Correct answer: To run transactions off the main chain while remaining pegged to it, enabling scalability and experimentation
Sidechains operate independently but are linked to the main chain via a two-way peg, allowing assets to move between chains and offloading traffic from the mainchain.
Question 7: What is the 'blockchain trilemma' as described by Ethereum co-founder Vitalik Buterin?
- The trade-off between mining rewards, transaction fees, and block time
- The difficulty of simultaneously achieving decentralization, security, and scalability (Correct answer)
- The challenge of supporting public, private, and consortium chains on one platform
- The conflict between token supply, demand, and price stability
Correct answer: The difficulty of simultaneously achieving decentralization, security, and scalability
The blockchain trilemma states that a network can typically optimize for only two of three properties — decentralization, security, and scalability — at any given design point.
CBCP Blockchain Fundamental 4
In blockchain, what is a 'mempool' (memory pool)?