Securing Blockchain Transactions with Cryptographic Techniques BFC Practice Questions (Page 3)

Questions 11–15

1. 11application · medium

   A user wants to receive cryptocurrency from a friend. The user shares their public address, which is derived from their public key. What can the friend do with this information?

   • AEncrypt messages to the user using the public address.
   • BSend cryptocurrency to the address and verify the user's signature on future transactions.
   • CDerive the user's private key from the public address.
   • DSpend the cryptocurrency stored at that address.
   Reveal Solution Discussion Select an answer first
2. 12application · medium

   A user reports that a transaction they signed was replayed on the network, causing an unintended duplicate payment. The blockchain uses a simple account-based model. Which mitigation should the development team implement to prevent this type of attack?

   • ARequire the user to sign the transaction with a different private key each time.
   • BInclude a unique nonce or sequence number in each transaction that is checked by the network.
   • CUse a stronger hash function for the transaction signature.
   • DEncrypt the transaction data with the recipient's public key.
   Reveal Solution Discussion Select an answer first
4. 13application · medium

   A developer is creating a new blockchain address format. They want to reduce the risk of users sending funds to a mistyped address. Which technique is most effective?

   • AUse the public key directly as the address.
   • BEncrypt the address with the user's public key.
   • CUse a longer hash function to generate the address.
   • DAdd a checksum to the address, such as a Base58Check encoding.
   Reveal Solution Discussion Select an answer first
5. 14expert · hard

   A proof-of-stake blockchain is considering a change to its block proposal selection. Currently, the chance of being selected is proportional to the number of coins staked. A security auditor warns that this creates a risk where an attacker with a large stake could dominate block production. Which cryptographic enhancement would most directly reduce this risk?

   • AUse a verifiable random function (VRF) to select the proposer, making the outcome unpredictable and publicly verifiable.
   • BSwitch to a longer hash function for block hashing.
   • CRequire all transactions to be signed with a hardware wallet.
   • DIncrease the block size to allow more transactions per block.
   Reveal Solution Discussion Select an answer first
6. 15expert · hard

   A blockchain-based voting system needs to ensure voter privacy (so that votes cannot be linked to voters) while also ensuring that each voter can vote only once and that the final tally is verifiable. Which cryptographic approach best satisfies these conflicting requirements?

   • AEncrypt each vote with the voter's public key and store it on the blockchain.
   • BUse a symmetric key shared among all voters to encrypt votes.
   • CUse a simple digital signature on each vote and store the votes in plaintext.
   • DUse a commitment scheme where each voter commits to their vote, then a mixing service anonymizes the votes, and finally a zero-knowledge proof verifies the tally without revealing individual votes.
   Reveal Solution Discussion Select an answer first