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Blockchain and Transaction Mechanics Flashcards

7 cards from real CBP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Blockchain and Transaction Mechanics flashcards as text

  1. What is a Replace-By-Fee (RBF) transaction?

    Answer: An unconfirmed transaction that can be replaced in the mempool with a higher-fee version

    RBF (BIP 125) allows the sender to broadcast a replacement transaction with a higher fee while the original is still unconfirmed in the mempool.

  2. Which Bitcoin script type pays directly to a hashed public key and is the most common legacy address format?

    Answer: P2PKH (Pay-to-Public-Key-Hash)

    P2PKH (Pay-to-Public-Key-Hash) hashes the public key with SHA-256 then RIPEMD-160, producing the familiar '1...' address format used by most legacy wallets.

  3. What enables a multi-signature Bitcoin wallet requiring 2-of-3 signers using a P2SH address?

    Answer: The redeem script encodes the multisig policy, and its hash becomes the P2SH address

    In P2SH multisig, the redeem script containing all three public keys and the 2-of-3 requirement is hashed to create the address; the script is only revealed when spending.

  4. What is Child-Pays-For-Parent (CPFP) fee bumping?

    Answer: Spending an unconfirmed output with a high-fee child transaction to incentivize miners to confirm both

    CPFP lets a recipient (or change owner) spend an unconfirmed output in a high-fee child transaction, motivating miners to mine both parent and child together for combined fees.

  5. What is the function of the Bitcoin mempool?

    Answer: It holds unconfirmed transactions waiting to be selected and included in a block by miners

    The mempool (memory pool) is a node's local buffer of valid but unconfirmed transactions that miners select from when assembling a new block.

  6. How does Bitcoin prevent double-spending in the absence of a central authority?

    Answer: Through the distributed blockchain where the longest chain of accumulated Proof-of-Work defines valid history

    The Bitcoin network reaches consensus on transaction order via Proof-of-Work; the chain with the most accumulated work is accepted as canonical, making double-spends extremely costly to execute.

  7. What is a transaction malleability attack in the context of pre-SegWit Bitcoin?

    Answer: An attacker alters non-essential signature data to change a transaction's TXID without invalidating it

    Pre-SegWit, the scriptSig (including signature encoding) was part of the TXID hash; small malleations to DER-encoded signatures could change the TXID while keeping the transaction valid.