Merkle Trees Checkpoint

Reconstruct states, diagnose implementation errors, and identify what the model guarantees.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. A level-array tree begins with nine leaf hashes. How many sibling hashes are in a proof for any one leaf? Enter one integer.

2. A proof step has Left=true. If h is the current hash and s the supplied sibling, which parent is required?

Select one answer.

H(h || s) H(s || h) H(h) || H(s) H(sort(h,s))

3. What does a successful empty proof establish for leaf X and expected root R?

Select one answer.

The original tree was empty The original tree had exactly one leaf H(X) equals R The caller used a valid index

4. Which pair of lists has equal roots because of odd duplication, without requiring a hash collision?

Select one answer.

[P] and an empty list for arbitrary P [P,Q,R] and [P,Q,R,R] [P,Q,R] and [P,R,Q] for arbitrary distinct P,Q,R [P,Q] and [Q,P] for arbitrary distinct P,Q

5. A server supplies a transaction, its proof, and a root chosen by that server. Verification succeeds. What is still missing to establish inclusion relative to an accepted block?

Select one answer.

An independently accepted block root to compare against A second execution of the same hash function A longer proof even if the existing path is correct The complete transaction list in every case

6. Starting only from n raw leaves, what does an O(log n)-size proof imply about the straightforward proof generator?

Select one answer.

It never needs to hash the requested leaf It still builds the tree in O(total leaf bytes+n) work It must store an exponential number of hashes It hashes only O(log n) leaves

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