Securing Blockchain Transactions with Cryptographic Techniques BFC Practice Questions (Page 2)

Questions 6–10

1. 6application · medium

   A developer is implementing a wallet that generates a new address for each incoming payment. They want to ensure that the address is derived from the public key in a way that prevents an attacker from deriving the private key from the address. Which practice should they follow?

   • AEncrypt the private key with a passphrase and use the encrypted value as the address.
   • BGenerate a random private key, derive the public key, and then hash the public key to produce the address.
   • CUse the public key directly as the address without any hashing.
   • DUse the private key directly as the address to avoid any transformation.
   Reveal Solution Discussion Select an answer first
2. 7foundation · easy

   What is a common cryptographic attack on blockchain transactions where an attacker intercepts and alters a transaction before it is confirmed?

   • ADenial-of-service (DoS) attack
   • BSybil attack
   • CReplay attack
   • DMan-in-the-middle (MITM) attack
   Reveal Solution Discussion Select an answer first
4. 8application · medium

   A blockchain game company stores user private keys in a database. A breach exposes the database, and attackers are able to sign transactions on behalf of users. Which additional control would have most likely prevented this?

   • AUsing a hardware security module (HSM) to store the keys and perform signing operations.
   • BEncrypting the private keys with a key derived from a passphrase stored in the same database.
   • CStoring the private keys in a separate table with restricted access.
   • DUsing a longer private key (e.g., 4096 bits instead of 256 bits).
   Reveal Solution Discussion Select an answer first
5. 9expert · hard

   A blockchain network is transitioning from proof-of-work to proof-of-stake to reduce energy consumption. The security team is concerned about the 'nothing at stake' problem, where validators might vote for multiple competing forks without cost. Which cryptographic or protocol mechanism directly addresses this problem?

   • AUsing a stronger hash function for block hashing.
   • BSlashing conditions that penalize validators who sign conflicting blocks, enforced by the protocol.
   • CEncrypting all block proposals with a shared symmetric key.
   • DRequiring validators to solve a cryptographic puzzle before each block proposal.
   Reveal Solution Discussion Select an answer first
6. 10expert · hard

   A blockchain network uses ECDSA with a deterministic nonce (RFC 6979). A developer, unaware of this, modifies the signing code to use a random nonce generated from a weak RNG. Which attack becomes possible, and what is the best fix?

   • AMan-in-the-middle attack; use TLS for node communication.
   • BHash collision attack; switch to a stronger hash function.
   • CReplay attack; add a timestamp to the transaction.
   • DNonce reuse attack; revert to deterministic nonce generation or use a CSPRNG.
   Reveal Solution Discussion Select an answer first