Securing Blockchain Transactions with Cryptographic Techniques BFC Practice Questions (Page 9)

Questions 41–45

1. 41expert · hard

   A blockchain-based voting platform uses Ed25519 signatures. An auditor discovers that the system generates private keys using a random number generator seeded with the current timestamp. Which cryptographic attack is the most immediate risk, and what is the best mitigation?

   • AKey reuse attack; mitigate by deriving a unique nonce for each signature.
   • BMan-in-the-middle attack on the signing protocol; mitigate by using TLS for all communications.
   • CPrivate key recovery due to insufficient entropy; mitigate by using a cryptographically secure random number generator (CSPRNG).
   • DBirthday attack on the hash function; mitigate by switching to SHA-512.
   Reveal Solution Discussion Select an answer first
2. 42application · medium

   A legal firm is using a blockchain to record contract signatures. They need to prove in court that a specific party signed a specific document and that the document has not been altered since signing. Which combination of cryptographic techniques should they use?

   • AStore the document's hash on the blockchain and rely on the party's password to authenticate.
   • BEncrypt the document with the party's public key and store the encrypted document on the blockchain.
   • CUse a symmetric key to encrypt the document and share the key with the court.
   • DHash the document, sign the hash with the party's private key, and store the signature and hash on the blockchain.
   Reveal Solution Discussion Select an answer first
4. 43foundation · easy

   Why is it important to generate a private key using a secure random number generator?

   • ATo make the key unpredictable and resistant to guessing attacks
   • BTo allow the key to be recovered if lost
   • CTo ensure the key is long enough to be memorable
   • DTo ensure the key is compatible with all blockchain networks
   Reveal Solution Discussion Select an answer first
5. 44application · medium

   A cryptocurrency exchange is designing a new hot wallet for daily operations. They want to generate a large number of addresses without storing each private key individually. Which approach is most appropriate?

   • AUse a hierarchical deterministic (HD) wallet with a single master seed to derive child keys and addresses.
   • BDerive addresses from the public key without any private key.
   • CUse the same private key for all addresses to simplify management.
   • DGenerate each address from a random number and store the private keys in a database.
   Reveal Solution Discussion Select an answer first
6. 45application · medium

   A supply-chain consortium records product provenance on a permissioned blockchain. Each node stores a full copy of the ledger. A member wants to verify that a specific transaction has not been altered since it was committed, without downloading the entire ledger. Which mechanism, combined with the block header, provides this capability?

   • AA Merkle root stored in the block header, allowing a Merkle proof for the transaction.
   • BThe previous block's hash, which links the chain.
   • CThe block's timestamp, which confirms when the block was created.
   • DThe transaction's digital signature, which proves the sender's identity.
   Reveal Solution Discussion Select an answer first