AES Fundamentals Quiz
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Questions and Answers

What is the primary characteristic of the Advanced Encryption Standard (AES)?

  • It is a asymmetric cipher.
  • It is the most widely used symmetric cipher. (correct)
  • It was developed solely by RSA Laboratories.
  • It uses a fixed key length of 128 bits only.

    • What key lengths does AES support?

  • 128, 192, and 256 bits (correct)
  • 64, 128, and 192 bits
  • 256 and 512 bits only
  • 128 and 512 bits only

    • Which of the following layers is NOT part of the internal structure of AES?

  • Byte Substitution layer
  • Diffusion layer
  • Key Addition layer
  • Block Generation layer (correct)

    • Which organization announced the need for a new block cipher in January 1997?

    <p>National Institute of Standards and Technology (NIST)</p> Signup and view all the answers

    Which of the following is a requirement for AES candidate submissions?

    <p>Efficient in both software and hardware</p> Signup and view all the answers

    When were the 5 finalists for the AES selection announced?

    <p>August, 1999</p> Signup and view all the answers

    Which algorithm was not one of the finalists in the AES selection?

    <p>AES-256</p> Signup and view all the answers

    What is the block size requirement for AES submissions?

    <p>128-bit block size</p> Signup and view all the answers

    What is a requirement for the AES algorithm regarding software implementation?

    <p>It must allow efficient software implementation.</p> Signup and view all the answers

    What is the purpose of the decryption key schedule in AES?

    <p>To require all subkeys to be used in reversed order.</p> Signup and view all the answers

    Which of the following key lengths is supported by AES?

    <p>128 bits</p> Signup and view all the answers

    What is the primary security concern associated with side-channel attacks?

    <p>They exploit implementation weaknesses of the algorithm.</p> Signup and view all the answers

    What is the result of using a sophisticated approach in AES for software implementation?

    <p>It integrates all round functions into one table look-up.</p> Signup and view all the answers

    Why is a brute-force attack not feasible against AES?

    <p>The key lengths of 128, 192, or 256 bits provide strong security.</p> Signup and view all the answers

    Which component is NOT part of the internal structure of AES?

    <p>Feedback layer</p> Signup and view all the answers

    What advantage does AES provide against analytical attacks?

    <p>No known analytical attack is better than brute-force against AES.</p> Signup and view all the answers

    What is the purpose of the Inv MixColumn layer in AES decryption?

    <p>It reverses the MixColumn operation by multiplying columns with an inverse matrix.</p> Signup and view all the answers

    Which layer in the AES algorithm is its own inverse?

    <p>Key Addition layer</p> Signup and view all the answers

    How does the Inv ShiftRows layer manipulate the state matrix during decryption?

    <p>It shifts rows to the right based on their index.</p> Signup and view all the answers

    What is the role of the inverse S-Box during AES decryption?

    <p>To replace output bytes with corresponding input bytes.</p> Signup and view all the answers

    In AES, what type of arithmetic operations are performed for the Inv MixColumn layer?

    <p>Operations in the Galois field GF(2^8).</p> Signup and view all the answers

    What occurs during the Inv Byte Substitution layer of AES decryption?

    <p>The inverse of the S-Box is applied to each byte.</p> Signup and view all the answers

    Which of the following statements is true regarding the structure of AES?

    <p>AES includes a diffusion layer as part of its structure.</p> Signup and view all the answers

    What transformation does the Inv ShiftRows layer apply to the second row of the state matrix?

    <p>One position right shift.</p> Signup and view all the answers

    In the context of the AES decryption process, what is the significance of using the inverse S-Box?

    <p>It allows for reversible encryption when decoding.</p> Signup and view all the answers

    What is the number of rounds used in AES for a 256-bit key?

    <p>14</p> Signup and view all the answers

    What type of operation is performed in the MixColumn sublayer of AES?

    <p>Matrix multiplication</p> Signup and view all the answers

    How is the state in AES organized?

    <p>4x4 matrix of bytes</p> Signup and view all the answers

    What property do the S-Boxes in the Byte Substitution layer of AES have?

    <p>They are reversible.</p> Signup and view all the answers

    What is the function of the Key Addition layer in AES?

    <p>Combine state matrix with a subkey</p> Signup and view all the answers

    What does the ShiftRows operation in the Diffusion layer do?

    <p>Shifts rows cyclically</p> Signup and view all the answers

    What is the primary reason for using multiple rounds in AES?

    <p>To enhance security through complexity</p> Signup and view all the answers

    How many subkeys are produced when using a 128-bit key in AES?

    <p>11</p> Signup and view all the answers

    In the MixColumn transformation, what is the mathematical field utilized for operations?

    <p>Galois field GF(2^8)</p> Signup and view all the answers

    Which layer in AES is primarily responsible for diffusion?

    <p>Diffusion layer</p> Signup and view all the answers

    What type of transformation is the Byte Substitution layer in AES?

    <p>Non-linear transformation</p> Signup and view all the answers

    What is a key feature of the AES algorithm?

    <p>It is primarily a block cipher.</p> Signup and view all the answers

    What determines the number of rounds in AES?

    <p>The length of the key</p> Signup and view all the answers

    What structure does the Cipher use to arrange the input data in AES?

    <p>A matrix</p> Signup and view all the answers

    Study Notes

    Advanced Encryption Standard (AES)

    • AES is the most prevalent symmetric cipher currently used.
    • Its algorithm was selected by NIST through a multi-year process.
    • Criteria for AES candidates included: 128-bit block size; three key lengths (128, 192, and 256 bits); security relative to other algorithms; efficiency in software and hardware.

    AES Selection Chronology

    • NIST announced the need for a new block cipher in January 1997.
    • Fifteen candidate algorithms were accepted in August 1998.
    • Five finalists were announced in August 1999:
      • Mars (IBM)
      • RC6 (RSA)
      • Rijndael (Daemen & Rijmen)
      • Serpent (Biham et al.)
      • Twofish (Schneier et al.)
    • Rijndael was chosen as AES in October 2000.
    • AES was officially adopted as a US federal standard in November 2001.

    AES Overview

    • AES is a byte-oriented cipher.
    • The 128-bit data (state) is arranged into a 4x4 matrix.
    • The number of rounds in AES depends on the key length:
      • 128 bits: 10 rounds
      • 192 bits: 12 rounds
      • 256 bits: 14 rounds

    AES Internal Structure

    • Each round except the last comprises these layers:
      • Byte Substitution layer: Uses 16 S-Boxes. These are the sole non-linear parts of AES.
      • ShiftRows layer: Cyclically shifts the rows of the state matrix.
      • MixColumns layer: A linear transformation that mixes the columns.
      • Key Addition layer: XORs the current state with a subkey.
    • The last round omits the MixColumns layer.

    Key Schedule

    • Subkeys are derived recursively from the input key.

    • Each round gets a subkey, and an extra one is used at the start of AES.

    • The number of subkeys depends on these key lengths:

      • 128 bits: 11 subkeys
      • 192 bits: 13 subkeys
      • 256 bits: 15 subkeys

    • Key whitening occurs at both input & output; subkeys and rounds are correlated; identical key schedules for each key size are used.

    AES Implementation (Software)

    • Software implementations can accomplish merging all round functions (besides key addition) into a look-up table (LUT).
    • This results in four 256-entry tables, each entry with 32 bits.
    • Computes a round of AES using 16 LUT lookups.
    • Modern 64-bit processors support speeds approaching 1.6 Gbit/s for AES

    AES Security

    • AES is resistant to brute-force attacks due to the key lengths.
    • No known analytical attacks are superior to brute-force.
    • Side-channel attacks, though, target vulnerabilities in implementation rather than the algorithm itself..

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    UNIT4 The Advanced Encryption Standard (AES) PDF

    Description

    Test your knowledge on the Advanced Encryption Standard (AES) with this quiz. Explore its key characteristics, structure, and the selection process that established AES as a core cryptographic framework. Perfect for students and professionals in computer security.

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