Feistel Networks, DES, 3DES, and AES ECES Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A developer is implementing AES in hardware and wants to understand the purpose of each transformation. Which statement correctly describes the role of the MixColumns step?

   • AIt provides diffusion by mixing bytes within each column of the state.
   • BIt provides confusion by substituting each byte with a value from the S-box.
   • CIt shifts rows of the state to spread bytes across columns.
   • DIt XORs the round key with the state to incorporate the key.
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2. 2foundation · easy

   What is the block size of AES?

   • A256 bits
   • B128 bits
   • C64 bits
   • D192 bits
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4. 3foundation · easy

   In the DES algorithm, what is the purpose of the initial permutation (IP) and final permutation (FP)?

   • AThey are used to generate the 16 subkeys from the main key
   • BThey rearrange bits of the block before and after the 16 Feistel rounds
   • CThey are optional and can be omitted without affecting security
   • DThey expand the block from 64 bits to 128 bits before encryption
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5. 4application · medium

   You are reviewing an AES implementation and notice that the key expansion routine generates round keys that are each 128 bits long. The implementation is configured for AES-192. How many round keys are generated in total?

   • A12 round keys
   • B14 round keys
   • C16 round keys
   • D13 round keys
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6. 5expert · medium

   A company is migrating from 3DES to AES for encrypting data at rest. They have a large installed base of hardware that only supports 3DES, but they are planning to replace it over the next two years. During the transition, they must maintain interoperability with partners who still use 3DES. Which approach best balances security and interoperability?

   • AUse 3DES with two keys for internal storage and AES for external communications.
   • BUse AES-128 for internal storage and 3DES for all external communications.
   • CContinue using 3DES with three independent keys until all partners upgrade, then switch to AES.
   • DUse AES-256 for all new data and provide a gateway that translates between AES and 3DES for partner communications.
   Reveal Solution Discussion Select an answer first