Securing Blockchain Transactions with Cryptographic Techniques BFC Practice Questions (Page 8)

Questions 36–40

1. 36application · medium

   A user claims they never authorized a particular transaction on a blockchain. The transaction is signed with the user's private key. Which property of digital signatures makes it difficult for the user to deny this?

   • ANon-repudiation, because a valid signature can only be produced by the holder of the private key.
   • BAvailability, because the signature is stored on the blockchain.
   • CConfidentiality, because the transaction content is encrypted.
   • DIntegrity, because the hash of the transaction is included in the signature.
   Reveal Solution Discussion Select an answer first
2. 37application · medium

   A blockchain startup is building a mobile wallet. They want to allow users to recover their funds if they lose their phone. Which approach is the most secure and user-friendly?

   • AUse a mnemonic seed phrase that the user writes down and stores offline.
   • BBack up the private key to the user's cloud account.
   • CStore the private key on the phone's internal storage and rely on the phone's lock screen.
   • DSend the private key to the user's email address.
   Reveal Solution Discussion Select an answer first
4. 38foundation · easy

   How does a digital signature provide non-repudiation in a blockchain transaction?

   • ABy including a timestamp that proves when the transaction was sent
   • BBy encrypting the transaction so only the recipient can read it
   • CBy requiring a third party to confirm the transaction
   • DBy proving that the transaction was created by the holder of the private key
   Reveal Solution Discussion Select an answer first
5. 39application · medium

   A blockchain network uses a proof-of-work consensus mechanism. Miners compete to find a nonce such that the block header hash is below a target. An attacker wants to secretly mine an alternative chain to double-spend. Which property of the hash function makes this attack computationally expensive?

   • ACollision resistance: it is hard to find two different block headers that produce the same hash.
   • BPreimage resistance: given a target hash, it is infeasible to find an input that produces that hash.
   • CAvalanche effect: a small change in the block header produces a completely different hash.
   • DDeterminism: the same block header always produces the same hash.
   Reveal Solution Discussion Select an answer first
6. 40foundation · easy

   How is a blockchain address typically derived from a public key?

   • ABy applying a cryptographic hash function to the public key
   • BBy using the public key directly without any transformation
   • CBy reversing the private key
   • DBy encrypting the public key with a symmetric cipher
   Reveal Solution Discussion Select an answer first