Securing Blockchain Transactions with Cryptographic Techniques BFC Practice Questions (Page 4)

Questions 16–20

1. 16foundation · easy

   What is the primary purpose of the public key in a blockchain transaction?

   • ATo allow others to verify the authenticity of a digital signature
   • BTo decrypt the transaction data so the recipient can read it
   • CTo sign the transaction on behalf of the sender
   • DTo generate the private key from the public key
   Reveal Solution Discussion Select an answer first
2. 17foundation · easy

   What is a key difference between symmetric and asymmetric encryption?

   • AAsymmetric encryption is faster than symmetric encryption
   • BSymmetric encryption requires a public key infrastructure, while asymmetric does not
   • CSymmetric encryption uses one key for both encryption and decryption, while asymmetric uses a pair of keys
   • DSymmetric encryption is always more secure than asymmetric encryption
   Reveal Solution Discussion Select an answer first
4. 18application · medium

   A blockchain-based supply chain platform uses SHA-256 to hash each shipment record before storing it on-chain. An auditor discovers that two different shipment records produce the same hash value. What is the most immediate security concern, and what mitigation should be applied?

   • AThis is a length-extension attack; the platform should use HMAC instead of plain hashing.
   • BThis is a birthday attack; the platform should use a longer hash output, such as SHA-256 with a different initialization vector.
   • CThis is a hash collision; the platform should switch to a stronger hash function like SHA-512 or a SHA-3 variant.
   • DThis is a preimage attack; the platform should add a random salt to each record before hashing.
   Reveal Solution Discussion Select an answer first
5. 19expert · hard

   A blockchain wallet generates addresses by hashing the public key. An attacker has developed a method to find a public key that hashes to the same address as a victim's address, but they do not have the corresponding private key. What is the impact of this attack, and what is the best mitigation?

   • AThe attacker could reverse the hash to find the private key; the mitigation is to use a salt.
   • BThe attacker could impersonate the victim in transactions; the mitigation is to use a hardware wallet.
   • CThe attacker could spend funds from the victim's address; the mitigation is to use a digital signature with a timestamp.
   • DThe attacker could receive funds sent to the victim's address, but they cannot spend funds already sent to the victim's address; the mitigation is to use a longer hash output for addresses.
   Reveal Solution Discussion Select an answer first
6. 20foundation · easy

   Which mitigation is effective against a replay attack on a blockchain transaction?

   • AUsing a longer private key
   • BUsing a unique transaction nonce or sequence number
   • CIncreasing the transaction fee
   • DEncrypting the transaction with the recipient's public key
   Reveal Solution Discussion Select an answer first