Bitcoin and Bitcoin Blockchain Architecture BDC Practice Questions (Page 1)

Questions 1–5

1. 1expert · hard

   A security researcher is analyzing a potential 51% attack on Bitcoin. The attacker controls more than half of the network's hashrate. Which of the following actions can the attacker reliably perform?

   • ASteal bitcoins from addresses that do not belong to the attacker.
   • BChange the block reward to any amount the attacker chooses.
   • CPrevent any transactions from ever being confirmed again.
   • DDouble-spend transactions by mining a longer alternative chain that excludes those transactions.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A developer is examining a Bitcoin block and wants to determine the total amount of new bitcoins created in that block. Which field should the developer look at?

   • AThe Merkle root.
   • BThe coinbase transaction's output value.
   • CThe difficulty bits.
   • DThe block header's nonce.
   Reveal Solution Discussion Select an answer first
4. 3application · medium

   A developer is explaining to a client why Bitcoin nodes accept a new block as valid even though the block's transactions might conflict with a previous block. Which property of Proof of Work makes it economically impractical for an attacker to rewrite history?

   • AThe block reward halving schedule
   • BThe size of the transaction fees
   • CThe cumulative difficulty of the chain
   • DThe timestamp of the block
   Reveal Solution Discussion Select an answer first
5. 4foundation · easy

   How does Proof of Work achieve consensus in the Bitcoin network?

   • AMiners vote on each transaction, and the majority decides
   • BAll nodes must approve every transaction before it is added to a block
   • CMiners compete to find a hash below a target, and the first valid block is added to the chain
   • DA central authority selects which miner creates the next block
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   A developer is creating a Bitcoin smart contract that allows funds to be spent either by Alice's signature immediately or by Bob's signature after a certain block height. Which Bitcoin Script pattern should be used?

   • AA conditional script using OP_IF and OP_CHECKLOCKTIMEVERIFY
   • BA simple script with only Alice's public key
   • CA hash-locked script that requires a preimage
   • DA multi-signature script requiring both Alice and Bob to sign
   Reveal Solution Discussion Select an answer first