Advanced Cryptographic Mechanisms BDC Practice Questions (Page 2)

Questions 6–10

1. 6expert · hard

   A developer is designing a blockchain for a voting system where voters must be able to verify that their vote was counted, but no one else should be able to see how they voted. The system also needs to prevent vote selling. Which combination of cryptographic mechanisms is most effective?

   • AZero-knowledge proofs of correct tallying and a receipt that does not reveal the vote
   • BSymmetric encryption of votes with a shared key and a public tally
   • CHomomorphic encryption for tallying and a receipt that reveals the vote to the voter
   • DDigital signatures on each vote and a public list of votes
   Reveal Solution Discussion Select an answer first
2. 7expert · hard

   A blockchain developer is evaluating cryptographic algorithms for a new proof-of-stake network. The network must be resistant to long-range attacks where an attacker who obtains old private keys could rewrite history. Which mechanism is specifically designed to mitigate this type of attack?

   • AUsing a fixed public key for all validators
   • BEncrypting all historical blocks with a network-wide key
   • CRelying on a centralized checkpoint authority
   • DKey-evolving signatures where the signing key changes over time
   Reveal Solution Discussion Select an answer first
4. 8application · medium

   A developer is designing a private blockchain for a healthcare network. Patient records are stored off-chain, but the blockchain stores a commitment to each record. The requirement is that a patient can later prove that a specific record was part of the system at a certain time without revealing the record's content. Which mechanism should be used?

   • AEncrypt the record and store the ciphertext on-chain
   • BUse a digital signature of the record by the hospital
   • CStore the patient's public key on-chain
   • DA cryptographic hash of the record stored on-chain with a timestamp
   Reveal Solution Discussion Select an answer first
5. 9expert · hard

   A healthcare blockchain must comply with data protection regulations that require the ability to delete a patient's data upon request. However, the blockchain is immutable. The architect is evaluating advanced cryptographic mechanisms to reconcile these requirements. Which approach is most viable?

   • AUse a ring signature to anonymize the patient's identity, making the data untraceable.
   • BUse homomorphic encryption to store patient data on-chain, allowing computations without decryption.
   • CUse a zero-knowledge proof to prove that the data existed, without storing the data on-chain.
   • DStore only hashes of patient data on-chain, and keep the actual data off-chain in a deletable database.
   Reveal Solution Discussion Select an answer first
6. 10expert · hard

   A consortium blockchain for cross-border payments must satisfy two conflicting requirements: regulators need to audit the full transaction history, while member banks want to keep their trading partners confidential. The solution must also minimize the computational overhead on the validating nodes. Which approach best balances these constraints?

   • AUse fully homomorphic encryption for all transaction data, allowing regulators to compute audits on encrypted data.
   • BEncrypt the counterparty information with a key shared only among regulators.
   • CUse a zero-knowledge proof for each transaction that proves regulatory compliance without revealing the counterparty.
   • DUse a ring signature to hide the identity of the sender, but keep the transaction amount plaintext.
   Reveal Solution Discussion Select an answer first