Advanced Cryptography CAS-005 Practice Questions (Page 4)

Questions 16–20

1. 16application · medium

   A company stores user passwords using a salted hash. The security team wants to increase the difficulty of brute-force attacks, especially considering the future threat of quantum computers. Which approach is most effective?

   • AUse a symmetric encryption algorithm like AES-256 to encrypt the password hashes.
   • BUse a longer salt (e.g., 256 bits) to prevent rainbow table attacks.
   • CUse a post-quantum signature algorithm like CRYSTALS-Dilithium to sign the password hashes.
   • DUse a key stretching function like Argon2 with a high memory and time cost.
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2. 17foundation · easy

   Which of the following is a common key stretching algorithm?

   • ASHA-256
   • BAES-256
   • CPBKDF2
   • DRSA-2048
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4. 18expert · hard

   A healthcare analytics firm wants to allow a third-party research organization to compute the average patient age and the total number of patients with a specific condition, without exposing individual patient records. The data is sensitive and must remain encrypted at all times. The firm is evaluating homomorphic encryption. Which consideration is most critical when deciding whether to use fully homomorphic encryption (FHE) for this workload?

   • AFHE operations are computationally intensive, so the performance overhead may be prohibitive for large datasets.
   • BFHE is only applicable to integer arithmetic, so it cannot compute averages or counts.
   • CFHE requires the use of a trusted third party to hold the decryption keys, which introduces a single point of failure.
   • DFHE is vulnerable to quantum attacks, so it must be combined with post-quantum algorithms.
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5. 19expert · hard

   A bank wants to allow a third-party auditor to verify that its loan approval process meets regulatory criteria without revealing the specific financial data of individual applicants. The auditor needs to check that the average debt-to-income ratio of approved loans is below a threshold. The bank has a large dataset of encrypted loan applications. Which approach is most practical?

   • AUse a key stretching function to derive a key that the auditor can use to decrypt only the aggregate result.
   • BUse a trusted execution environment (TEE) on the auditor's server to decrypt and process the data.
   • CUse homomorphic encryption to compute the average on encrypted data and provide the encrypted result to the auditor, who decrypts only the aggregate.
   • DProvide the auditor with the decryption key and a filtered dataset that excludes names and account numbers.
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6. 20application · medium

   A security architect is planning a long-term data protection strategy for a government contractor that must keep classified documents confidential for at least 30 years. The contractor is concerned about the eventual availability of large-scale quantum computers. The current system uses RSA-2048 for key exchange and AES-256 for data encryption. Which approach best addresses the quantum threat while maintaining interoperability with existing systems?

   • AImplement perfect forward secrecy by using ephemeral Diffie-Hellman key exchange for all sessions.
   • BIncrease RSA key size to 4096 bits to provide sufficient security against quantum attacks.
   • CReplace RSA-2048 with a hybrid key exchange combining a post-quantum algorithm (e.g., CRYSTALS-Kyber) with an elliptic-curve key exchange, and continue using AES-256 for data encryption.
   • DReplace AES-256 with a post-quantum symmetric algorithm such as CRYSTALS-Dilithium for all data encryption.
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