Cryptographic Principles and Their Role in Blockchain BBLC Practice Questions (Page 4)

Questions 16–20

1. 16application · medium

   A user claims they never authorized a particular blockchain transaction. The transaction was signed with their private key. What property of digital signatures makes this claim difficult to sustain?

   • ANon-repudiation
   • BConfidentiality
   • CCollision resistance
   • DAvalanche effect
   Reveal Solution Discussion Select an answer first
2. 17foundation · easy

   What is the primary threat of quantum computing to current blockchain cryptography?

   • AIt could derive private keys from public keys, compromising digital signatures
   • BIt could break the cryptographic hash functions used in block linking
   • CIt could increase the block size limit automatically
   • DIt could make blockchain transactions irreversible
   Reveal Solution Discussion Select an answer first
4. 18expert · hard

   A blockchain-based voting system records each vote as a transaction. To ensure voter privacy, the system uses a mixnet to anonymize the voter's identity, but the vote content is stored in plaintext on-chain. An auditor wants to verify that a particular voter's ballot was counted correctly without revealing how they voted. Which cryptographic approach would allow this verification while preserving privacy?

   • AUse a zero-knowledge proof that the vote is valid (e.g., belongs to a set of valid choices) and that it was included in the tally, without revealing the actual vote.
   • BHash the vote and store the hash on-chain; the auditor compares the hash to the voter's submitted hash.
   • CEncrypt the vote with the auditor's public key and store the encrypted vote on-chain; the auditor decrypts to verify.
   • DUse a digital signature from the voter to sign the vote, and store the signature on-chain for later verification.
   Reveal Solution Discussion Select an answer first
5. 19foundation · easy

   Why are hardware wallets considered a secure method for storing private keys?

   • AThey store private keys in an offline, tamper-resistant device
   • BThey generate private keys using a public algorithm that is easy to remember
   • CThey encrypt private keys with a password that is stored in the cloud
   • DThey automatically back up private keys to a centralized server
   Reveal Solution Discussion Select an answer first
6. 20expert · hard

   A blockchain startup is building a mobile wallet for non-technical users. They want to ensure that users can recover their funds if they lose their phone, but they also want to prevent a thief who steals the phone from accessing the wallet. Which design best balances security and usability?

   • AGenerate a 12-word seed phrase and instruct the user to write it down and store it in a safe place; require the seed phrase to restore the wallet on a new device.
   • BStore the private key in the phone's secure enclave and require a biometric authentication to sign transactions.
   • CCombine a seed phrase stored in a secure enclave with biometric authentication, and offer a cloud backup of the seed phrase encrypted with a user-chosen password.
   • DUse a multi-signature wallet where the user holds one key and a trusted third party holds another; require both to sign transactions.
   Reveal Solution Discussion Select an answer first