Cryptographic Hash Functions and Their Uses BDC Practice Questions (Page 5)

Questions 21–25

1. 21application · medium

   A blockchain startup wants to allow light clients to verify that a specific transaction is included in a block without downloading the entire block. They plan to use a Merkle tree. What should the light client receive to perform this verification?

   • AThe transaction and the full list of all transactions in the block.
   • BThe transaction, the Merkle root, and the sibling hashes along the path to the root.
   • CThe transaction and the block header only.
   • DThe transaction and the digital signature of the block producer.
   Reveal Solution Discussion Select an answer first
2. 22foundation · easy

   Which property of a cryptographic hash function makes it infeasible to find any input that produces a given hash output?

   • APreimage resistance
   • BCollision resistance
   • CAvalanche effect
   • DSecond preimage resistance
   Reveal Solution Discussion Select an answer first
4. 23application · medium

   A developer is building a web application that stores user passwords. The team decides to use bcrypt with a cost factor of 12. A security review notes that the application is vulnerable to denial-of-service attacks because the login endpoint can be flooded with requests, causing high CPU usage. Which mitigation is most appropriate?

   • ACache the bcrypt hash for each username to avoid recomputing it.
   • BReduce the bcrypt cost factor to 4 to lower CPU usage.
   • CImplement rate limiting on the login endpoint and use a proof-of-work challenge before performing the bcrypt hash.
   • DSwitch to a faster hash function like SHA-256 to reduce CPU load.
   Reveal Solution Discussion Select an answer first
5. 24application · medium

   A developer is implementing a digital signature scheme for a document management system. They want to sign a large PDF file efficiently. According to standard practice, what should they sign?

   • AThe file name and metadata only.
   • BA random nonce generated at signing time.
   • CThe entire PDF file byte by byte.
   • DThe cryptographic hash of the PDF file.
   Reveal Solution Discussion Select an answer first
6. 25application · medium

   A fintech startup stores customer statements as PDF files in Azure Blob Storage. They need to detect any accidental or malicious modification to a file after upload. They plan to compute a hash of each file at upload time and store it in a database. Later, they recompute the hash and compare. Which property of cryptographic hash functions makes this approach valid?

   • AThe hash is fast to compute, so integrity checks do not slow down file retrieval.
   • BThe hash is deterministic: the same input always produces the same output.
   • CThe hash is preimage resistant, so the original file cannot be recovered from the hash.
   • DThe hash has a fixed output length regardless of input size.
   Reveal Solution Discussion Select an answer first