Merkle Tree-Based Transaction Verification BDC Practice Questions (Page 5)

Questions 21–25

1. 21application · medium

   A blockchain network stores blocks with up to 1,024 transactions. A developer is designing a lightweight verification service that must prove transaction inclusion to clients with minimal bandwidth. Which approach best achieves this goal?

   • ASend only the Merkle path (10 sibling hashes) for the transaction.
   • BSend the transaction and all sibling subtrees.
   • CSend the entire block to each client for verification.
   • DSend the transaction hash and the block header only.
   Reveal Solution Discussion Select an answer first
2. 22application · medium

   A blockchain developer is building a light client for a mobile wallet. The client needs to verify that a specific transaction is included in a block without downloading the entire block. The developer has the block header (which contains the Merkle root) and the transaction hash. What is the minimum additional data required to perform this verification?

   • AThe list of all transaction hashes in the block.
   • BThe previous block's Merkle root.
   • CThe transaction's raw data and the block's nonce.
   • DThe Merkle path: the sibling hashes at each level from the transaction leaf up to the root.
   Reveal Solution Discussion Select an answer first
4. 23expert · hard

   A developer is implementing a Merkle tree and notices that the hash function used is not collision-resistant. What is the most direct security impact on the Merkle tree?

   • AThe tree will be unbalanced
   • BAn attacker could potentially create a different transaction that produces the same leaf hash, allowing tampering without changing the root
   • CThe tree will be slower to compute
   • DThe root will be longer
   Reveal Solution Discussion Select an answer first
5. 24application · medium

   A developer is implementing a blockchain and wants to ensure that any modification to a transaction in a block is detectable by any node that stores the block header. Which design choice is most effective?

   • AStore the block's timestamp and difficulty in the header.
   • BStore the Merkle root of all transactions in the block header.
   • CStore the concatenation of all transaction hashes in the block header.
   • DStore the hash of each transaction in the block header.
   Reveal Solution Discussion Select an answer first
6. 25application · medium

   A developer is implementing a function that verifies a Merkle inclusion proof. The function receives a transaction hash, a Merkle path (list of sibling hashes), and the expected root. Which sequence of operations correctly verifies the proof?

   • ADecrypt the transaction hash using the sibling hashes to recover the root.
   • BHash the transaction hash repeatedly until it equals the expected root.
   • CStart with the transaction hash, then for each sibling in the path, concatenate and hash the current hash with the sibling (order based on position), and finally compare the result to the expected root.
   • DConcatenate all sibling hashes and hash them once, then compare to the expected root.
   Reveal Solution Discussion Select an answer first