Bitcoin Transactions and Mining Flashcards

An investigator is analyzing a Bitcoin transaction that has been broadcast to the network but has not yet been included in a block. In which of the following locations would the investigator most likely find this transaction?

Answer: The mempool of a Bitcoin node

When a Bitcoin transaction is broadcast, it enters a 'waiting area' called the mempool (memory pool) on Bitcoin nodes. Miners select transactions from the mempool to include in the next block. Therefore, an unconfirmed transaction resides in the mempool of the nodes on the network.

A Certified Cryptocurrency Investigator is examining the rewards a miner received for successfully mining a new block. This reward is composed of two distinct components. Which of the following correctly identifies these two components?

Answer: The block subsidy (newly created bitcoin) and the transaction fees from the included transactions.

A miner's reward for successfully adding a new block to the Bitcoin blockchain consists of two parts: the block subsidy, which is a predetermined amount of newly created bitcoin, and the sum of all transaction fees from the transactions included in that block.

An investigator is reviewing a series of transactions and notices that the fee paid for a $1 million transaction is the same as the fee for a $100 transaction. What is the primary factor that determines the cost of a Bitcoin transaction fee?

Answer: The transaction's data size in bytes and network congestion.

Bitcoin transaction fees are not based on the monetary value being transferred. Instead, they are primarily determined by the transaction's size in terms of data (bytes or virtual bytes) and the current level of network congestion. Miners prioritize transactions with higher fees per byte, especially when block space is limited.

A criminal organization attempts to disrupt the Bitcoin network by controlling over half of the network's mining power. They successfully reverse their own recent transactions, effectively spending the same bitcoins twice. What is this type of attack called?

Answer: A 51% Attack

A 51% attack occurs when a single entity or group controls more than 50% of a blockchain network's total mining hashrate. This majority control allows them to manipulate the blockchain, prevent new transactions from gaining confirmations, and reverse their own transactions, leading to double-spending.

The Bitcoin protocol includes a mechanism to ensure that, on average, a new block is added to the blockchain approximately every 10 minutes, regardless of changes in the total network hash rate. What is this self-regulating feature called?

Answer: The Difficulty Adjustment

The Bitcoin network automatically adjusts the 'difficulty' of the mathematical problem miners must solve every 2,016 blocks (roughly every two weeks). If blocks are being found too quickly (faster than 10 minutes on average), the difficulty increases. If they are found too slowly, it decreases. This is known as the difficulty adjustment.

Which of the following best describes an Unspent Transaction Output (UTXO) in the context of a Bitcoin investigation?

Answer: A specific, discrete amount of bitcoin that has been received but not yet spent, acting as an input for a future transaction.

The UTXO model is fundamental to how Bitcoin tracks ownership. Instead of balances in an account, a user's wallet holds a collection of UTXOs. Each UTXO is a discrete amount of bitcoin from a previous transaction's output that the user can now spend. When a new transaction is made, existing UTXOs are used as inputs.