Cryptographic Principles and Their Role in Blockchain BBLC Practice Questions (Page 7)

Questions 31–35

1. 31foundation · easy

   What is the purpose of a seed phrase (mnemonic phrase) in blockchain key management?

   • ATo encrypt the user's public key
   • BTo provide a public address for receiving funds
   • CTo store transaction history
   • DTo serve as a backup that can regenerate all associated private keys
   Reveal Solution Discussion Select an answer first
2. 32application · medium

   A user claims they never signed a particular transaction that transferred funds from their wallet. The blockchain network needs to verify the authenticity of the transaction without relying on the user's word. What process should the network use to confirm whether the transaction was genuinely signed by the user?

   • AUse the user's public key to verify the digital signature attached to the transaction against the transaction data.
   • BHash the transaction and compare it to the hash stored in the user's wallet software.
   • CDecrypt the transaction with the user's private key and compare the result to the original transaction data.
   • DAsk the user to provide their private key to prove they signed it.
   Reveal Solution Discussion Select an answer first
4. 33application · medium

   A startup is building a blockchain-based document signing service. They want users to sign documents with a private key stored on a hardware wallet, and they need the service to verify signatures without ever accessing the private key. Which combination of cryptographic components should the service use?

   • AA digital signature generated with the user's private key and verified with the user's public key
   • BPublic-key encryption with the user's public key to encrypt the document, and the private key to decrypt it
   • CA hash of the document encrypted with the user's public key, stored on-chain for verification
   • DA symmetric key derived from the user's password, used to sign the document
   Reveal Solution Discussion Select an answer first
5. 34foundation · easy

   In proof-of-work, what is the role of the nonce?

   • ATo be varied so that miners can find a hash that meets the difficulty target
   • BTo store the timestamp of the block
   • CTo encrypt the block's transactions
   • DTo provide a unique identifier for the block on the blockchain
   Reveal Solution Discussion Select an answer first
6. 35application · medium

   A fintech company is building a permissioned blockchain for interbank transfers. They need to ensure that only authorized banks can submit transactions and that each transaction cannot be repudiated by the sender. Which combination of cryptographic mechanisms should they implement?

   • ASign each transaction with the sender's private key and encrypt it with the sender's public key.
   • BUse a shared symmetric key for both signing and encryption to simplify key management.
   • CHash the transaction and encrypt the hash with the recipient's public key; send the hash along with the transaction.
   • DEncrypt each transaction with the recipient's public key and sign it with the sender's private key.
   Reveal Solution Discussion Select an answer first