Cryptographic Hash Functions and Their Uses BDC Practice Questions (Page 2)

Questions 6–10

1. 6application · easy

   A developer is building a file-sync service that must detect which files changed between two versions of a directory. The service stores a hash for each file. Which approach minimizes the amount of data that must be transferred to identify changes?

   • AStore a hash of the file name and compare those hashes.
   • BStore the file size and modification timestamp for each file and compare those metadata values.
   • CStore the full file content on the server and compare byte-by-byte over the network.
   • DStore a SHA-256 hash of each file's content and compare hashes between the client and server.
   Reveal Solution Discussion Select an answer first
2. 7application · medium

   A developer is designing a file-sharing system that must ensure the integrity of downloaded files. The system currently provides a SHA-256 hash of each file on the website. A user downloads a file and verifies the hash. Which additional measure would most effectively protect against a man-in-the-middle attack that could alter both the file and the published hash?

   • APublish the hash on a public forum that is not controlled by the developer.
   • BUse a longer hash, such as SHA-512, to make it harder to find a collision.
   • CPublish the hash over HTTPS and also sign the hash with the developer's private key.
   • DEncrypt the file with a symmetric key and provide the key on the website.
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4. 8application · medium

   A startup is building a user authentication system. They want to store passwords securely. They are considering using a fast hash like SHA-256 with a per-user salt. A security consultant advises against this. What is the primary reason?

   • ASHA-256 is not collision-resistant enough for password storage.
   • BFast hashes allow attackers to brute-force many password guesses per second.
   • CSHA-256 cannot be used with a salt.
   • DSHA-256 produces a hash that is too long to store in a database.
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5. 9application · medium

   In a blockchain, each block header contains the hash of the previous block header. How does this design ensure the integrity of the entire chain?

   • AIt makes the blockchain immutable by preventing any changes to transaction data.
   • BIt encrypts the transactions so they cannot be read.
   • CIf any block is altered, its hash changes, which invalidates all subsequent blocks.
   • DIt prevents miners from creating new blocks.
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6. 10application · medium

   A developer is updating a legacy authentication system that currently stores passwords as unsalted SHA-256 hashes. The compliance team requires that the new system resist offline brute-force attacks even if the database is leaked. Which approach best meets this requirement?

   • AUse a global static salt prepended to every password before applying SHA-256.
   • BUse SHA-512 with multiple iterations but no salt.
   • CUse a fast hash like SHA-256 with a per-user salt to minimize CPU load.
   • DUse a per-user random salt and a slow, memory-hard hash function such as Argon2id.
   Reveal Solution Discussion Select an answer first