Symmetric Encryption and Defensive Coding CASENET Practice Questions (Page 6)

Questions 26–30

1. 26foundation · easy

   Which statement best describes symmetric encryption?

   • AIt uses the same key for both encryption and decryption.
   • BIt uses a different key for each block of data.
   • CIt uses a public key for encryption and a private key for decryption.
   • DIt uses a key that is derived from the data being encrypted.
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2. 27foundation · easy

   What is the primary purpose of padding in block cipher encryption?

   • ATo ensure the plaintext length is a multiple of the block size.
   • BTo add randomness to the encryption key.
   • CTo increase the strength of the encryption algorithm.
   • DTo authenticate the sender of the message.
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4. 28application · medium

   A .NET developer is encrypting sensitive customer data before storing it in a database. The current code uses a hardcoded 256-bit key and a random IV generated once at application startup, reused for every record. The security review requires that each encrypted record be independently decryptable without storing the key in the database, and that the key be rotated quarterly. Which change best addresses the review findings?

   • AEncrypt the key with a public key and store it alongside the ciphertext, using a fixed IV for all records.
   • BKeep the hardcoded key but generate a new random IV for each record and store the IV in a separate table.
   • CStore the key in Azure Key Vault, generate a new random IV per encryption operation, and prepend the IV to the ciphertext.
   • DUse a deterministic IV derived from the record ID and store the key in the application config file.
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5. 29expert · medium

   A team is implementing encryption for a database that stores sensitive personal data. They need to support both equality searches and range queries (e.g., find records with a date between X and Y). Which approach is the most appropriate?

   • AUse AES-ECB for all columns because it preserves patterns that can be used for queries.
   • BUse order-preserving encryption (OPE) for the date column to support range queries, and a deterministic HMAC for equality searches on other columns.
   • CUse AES-CBC with a deterministic IV for all columns to support both equality and range queries.
   • DUse AES-GCM with a random IV for all columns and perform all queries in the application layer.
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6. 30application · medium

   A .NET application needs to encrypt data in a load-balanced environment where multiple web servers must be able to decrypt data encrypted by any other server. The team wants to avoid storing the key in the application code. What is the best approach?

   • AHardcode the same key in each server's web.config file.
   • BUse a key derived from the server's machine name.
   • CGenerate a different key on each server and share them via a network share.
   • DStore the key in Azure Key Vault and use Managed Identity to access it from all servers.
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