Cryptographic Hash Functions and Their Uses BDC Practice Questions (Page 3)

Questions 11–15

1. 11expert · hard

   A proof-of-work blockchain is considering switching from SHA-256 to a memory-hard hash function like Ethash to reduce the advantage of specialized ASIC miners. Which trade-off must the developers consider?

   • AMemory-hard functions are more resistant to length-extension attacks, improving security.
   • BMemory-hard functions are faster to verify, which reduces the time to validate blocks.
   • CMemory-hard functions produce shorter hashes, reducing block size.
   • DMemory-hard functions increase the memory required for mining, which may exclude some lightweight nodes but also make mining more accessible to general-purpose hardware.
   Reveal Solution Discussion Select an answer first
2. 12foundation · easy

   In a Merkle tree, what is stored at the root?

   • AThe list of all transaction IDs
   • BThe timestamp of the block
   • CThe hash of all the hashes of the transactions in the block
   • DThe public key of the block producer
   Reveal Solution Discussion Select an answer first
4. 13expert · hard

   A blockchain developer is optimizing a light client that verifies transactions using Merkle proofs. The client currently downloads the full Merkle path for each transaction it wants to verify. The developer wants to reduce the number of hashes the client must compute. Which optimization is most effective?

   • AReplace the Merkle tree with a simple list of transaction hashes and verify by comparing the list.
   • BCache the Merkle root and reuse it for multiple transactions in the same block.
   • CBatch multiple transaction proofs together and verify them against the same root in one pass.
   • DUse a sorted Merkle tree so that the client can verify a transaction by checking its position without hashing.
   Reveal Solution Discussion Select an answer first
5. 14expert · hard

   A blockchain developer is evaluating the security of a proposed consensus algorithm that uses a hash function to select the next block producer. The algorithm takes the current block hash and the public keys of all candidates, and selects the candidate whose public key hashes to the lowest value. Which attack is most concerning?

   • AA preimage attack to find a public key that hashes to a low value.
   • BA length-extension attack to predict the next block hash.
   • CA grinding attack where a candidate tries many different block hashes to find one that favors them.
   • DA collision attack to create two public keys with the same hash and vote twice.
   Reveal Solution Discussion Select an answer first
6. 15foundation · easy

   What does it mean for a cryptographic hash function to be deterministic?

   • AThe hash output changes randomly each time the function is called
   • BThe same input always produces the same hash output
   • CThe hash output is generated using a secret key
   • DThe hash output is always the same regardless of the input
   Reveal Solution Discussion Select an answer first