Merkle Tree-Based Transaction Verification BDC Practice Questions (Page 6)

Questions 26–30

1. 26application · medium

   A developer is testing a Merkle proof verification function. The function is given a transaction hash, a Merkle path, and a root. The verification fails. Which is the most likely cause?

   • AThe transaction is not the first in the block.
   • BThe root is not stored in the block header.
   • CThe Merkle path contains a hash from a different block.
   • DThe transaction hash is too long.
   Reveal Solution Discussion Select an answer first
2. 27application · medium

   A developer is implementing a Merkle tree for a block that contains two transactions, Tx1 and Tx2. The developer computes H1 = hash(Tx1) and H2 = hash(Tx2). What is the correct Merkle root?

   • Ahash( H1 + H2 )
   • Bhash( Tx1 + Tx2 )
   • CH1 + H2
   • Dhash( H1 ) + hash( H2 )
   Reveal Solution Discussion Select an answer first
4. 28application · medium

   A blockchain developer is explaining the block structure to a new team member. Which statement correctly describes the role of the Merkle root in a block?

   • AIt is the hash of the block's timestamp
   • BIt is the digital signature of the block producer
   • CIt is the hash of the previous block's header
   • DIt is a single hash that commits to all transactions in the block
   Reveal Solution Discussion Select an answer first
5. 29application · medium

   A developer is designing a blockchain for a resource-constrained IoT device that must verify whether a transaction is included in a block. The block contains 1024 transactions. The device has very limited bandwidth and memory. What is the most efficient approach for the device to verify inclusion?

   • ADownload all 1024 transactions and recompute the entire Merkle tree
   • BAsk a full node to confirm the transaction and trust the response
   • CRequest the block header and compare the transaction hash to the Merkle root
   • DRequest a Merkle proof containing the transaction hash and 10 sibling hashes, then recompute the root
   Reveal Solution Discussion Select an answer first
6. 30expert · hard

   A blockchain network uses a Merkle tree to commit to transactions. An attacker wants to modify a transaction in a block without changing the Merkle root. Which attack would be required for this to succeed?

   • AA 51% attack on the network
   • BA replay attack on the transaction
   • CA denial-of-service attack on full nodes
   • DA cryptographic hash collision on the modified transaction's hash
   Reveal Solution Discussion Select an answer first