Advanced Cryptographic Mechanisms in Blockchain Security BBLC Practice Questions (Page 4)

Questions 16–20

1. 16expert · hard

   A blockchain network currently uses ECDSA signatures and SHA-256 hashing. A risk assessment indicates that quantum computers could break ECDSA in the near future, but SHA-256 is considered quantum-resistant for collision resistance. Which upgrade path should the network take?

   • AReplace ECDSA with a post-quantum signature scheme while keeping SHA-256 for hashing.
   • BSwitch to RSA-4096 for signatures.
   • CIncrease ECDSA key size to 512 bits.
   • DReplace SHA-256 with a post-quantum hash function.
   Reveal Solution Discussion Select an answer first
2. 17foundation · easy

   How does a digital signature provide integrity for a blockchain transaction?

   • ABy including a hash of the transaction that is signed with the sender's private key
   • BBy storing the transaction in a tamper-proof hardware module
   • CBy using a timestamp from a trusted third party
   • DBy encrypting the transaction data so that only the recipient can read it
   Reveal Solution Discussion Select an answer first
4. 18application · medium

   A legal team is reviewing a blockchain-based contract platform. They need to prove that a specific party agreed to a contract at a specific time, and that the contract text has not been modified since signing. Which combination of cryptographic features provides this?

   • AEncrypting the contract with the party's public key and storing it on-chain.
   • BStoring the contract in a hash table with a random nonce.
   • CUsing a MAC with a shared secret between the two parties.
   • DDigital signature of the contract hash using the party's private key, timestamped by the blockchain.
   Reveal Solution Discussion Select an answer first
5. 19application · medium

   A blockchain platform stores transaction data in blocks. To allow lightweight clients to verify that a specific transaction is included in a block without downloading the entire block, the platform uses a Merkle tree. Which property of the Merkle tree makes this efficient verification possible?

   • AEach leaf is a hash of a transaction, and internal nodes are hashes of child nodes, allowing verification with only the hashes along the path to the root.
   • BThe root hash is computed by concatenating and hashing all transaction hashes in a single operation, so the client only needs the root.
   • CThe Merkle root is signed by the block producer, so the client only needs to verify the signature to confirm all transactions.
   • DThe tree stores the actual transaction data in internal nodes, so the client can retrieve the transaction directly from the root.
   Reveal Solution Discussion Select an answer first
6. 20application · medium

   A healthcare blockchain stores patient records encrypted. Researchers need to compute the average age of patients in a study without accessing the raw data. Which cryptographic approach would allow the computation to be performed on the encrypted data?

   • AUse a digital signature from each patient to authorize the researcher to decrypt the data.
   • BUse homomorphic encryption so that the average can be computed directly on ciphertexts.
   • CUse a zero-knowledge proof to prove the average is correct without revealing individual records.
   • DUse a hash of each record and compute the average of the hashes.
   Reveal Solution Discussion Select an answer first