Cryptographic Hash Functions and Their Uses BDC Practice Questions (Page 1)

Questions 1–5

1. 1expert · hard

   A company is migrating from a legacy password storage system that uses unsalted SHA-256 to a modern system. The migration must allow users to log in without resetting passwords. The security team wants to upgrade the hashes to Argon2id. Which migration strategy is most secure and practical?

   • AStore both the legacy hash and the new Argon2id hash for every user, and verify against either.
   • BRequire all users to reset their passwords during the migration window.
   • CImmediately rehash all existing SHA-256 hashes with Argon2id using a global salt.
   • DOn each successful login, verify the legacy SHA-256 hash, then rehash the password with Argon2id and a new salt, and update the stored record.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A blockchain developer is explaining to a client why altering a single transaction in a historical block would be detected by any full node. Which combination of hash-function properties and blockchain structure makes this detection possible?

   • ADeterminism and the nonce in the block header, which ensures the same block always hashes to the same value.
   • BThe avalanche effect and the chain of block headers, where each block header contains the hash of the previous header.
   • CPreimage resistance and the Merkle root in each block, which hides the transaction data.
   • DCollision resistance and the timestamp in each block, which prevents backdating.
   Reveal Solution Discussion Select an answer first
4. 3application · medium

   A developer is designing a system that stores file hashes for integrity monitoring. An attacker might try to replace a legitimate file with a malicious one that has the same hash. Which property of the hash function directly prevents this?

   • ACollision resistance
   • BDeterminism
   • CFixed output length
   • DPreimage resistance
   Reveal Solution Discussion Select an answer first
5. 4foundation · easy

   In a blockchain, how does the hash of a block contribute to the immutability of the chain?

   • AEach block contains the hash of the previous block, so altering a block changes its hash and breaks the chain
   • BThe hash of a block is stored in a central database, preventing changes
   • CThe hash of a block is used as the private key for the next block
   • DThe hash of a block is encrypted with the network's private key
   Reveal Solution Discussion Select an answer first
6. 5application · medium

   A security team is reviewing a system that uses a hash-based message authentication code (HMAC) with SHA-256. They are concerned about length-extension attacks. Which of the following is the best mitigation?

   • AUse SHA-256 without any key.
   • BUse MD5 instead of SHA-256.
   • CSwitch to plain SHA-256 of the message with a secret prefix.
   • DUse HMAC-SHA-256, which is designed to resist length-extension attacks.
   Reveal Solution Discussion Select an answer first