Advanced Cryptographic Mechanisms BDC Practice Questions (Page 3)

Questions 11–15

1. 11expert · hard

   A consortium blockchain for land registry needs to allow property owners to prove they own a property without revealing their identity to the public. The system must also allow a court to compel disclosure of the owner's identity in case of a legal dispute. Which cryptographic mechanism should be used?

   • AUse a zero-knowledge proof that the owner knows the private key associated with the property, without revealing the key.
   • BUse a homomorphic encryption of the owner's identity, with the key held by the court.
   • CUse a digital signature from the owner, with the owner's public key stored on-chain.
   • DUse a ring signature to hide the owner's identity, but allow a trusted authority to break the anonymity.
   Reveal Solution Discussion Select an answer first
2. 12expert · hard

   A developer is designing a blockchain-based identity system where users must be able to prove attributes (e.g., citizenship) to different verifiers without linking their activities across verifiers. Which cryptographic mechanism is designed to prevent verifiers from colluding to link a user's transactions?

   • AAnonymous credentials with selective disclosure
   • BStandard digital signatures with a certificate authority
   • CEncrypting the user's identity with a shared secret
   • DA single public key for all verifiers
   Reveal Solution Discussion Select an answer first
4. 13application · medium

   A blockchain platform uses a consensus algorithm where validators must agree on the order of transactions. An attacker wants to secretly alter a previously confirmed block without being detected. Which property of the blockchain's cryptographic design directly prevents this?

   • AValidators use symmetric keys for message authentication
   • BTransactions are encrypted with the validator's public key
   • CEach block contains the hash of the previous block
   • DThe genesis block is signed by the network founder
   Reveal Solution Discussion Select an answer first
5. 14application · medium

   A developer is implementing a blockchain for a gaming platform where players trade virtual items. The platform needs to ensure that a player cannot spend the same item twice. Which cryptographic concept is fundamental to preventing double-spending?

   • AUsing a digital signature on each transaction
   • BStoring transaction hashes in a Merkle tree
   • CA global ledger that records every transaction and is verified by consensus
   • DEncrypting each transaction with a unique key
   Reveal Solution Discussion Select an answer first
6. 15application · medium

   A developer is building a blockchain-based document signing service. The service must allow a user to sign a document and later prove that the signature was created by that user, but the service should not store the user's private key. Which mechanism should be used?

   • AA hash of the document stored on the server
   • BDigital signature generated with the user's private key on the user's device
   • CA shared secret key stored on the server
   • DEncrypting the document with the user's public key
   Reveal Solution Discussion Select an answer first