DES Encryption Algorithm
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Questions and Answers

What is the primary criterion for evaluating AES encryption?

  • Speed of encryption
  • Ciphertext block size
  • Key size
  • Security against practical cryptanalysis (correct)

    • What is the size of the data block in AES structure?

  • 4 columns of 8 bytes
  • 8 columns of 4 bytes
  • 4 columns of 4 bytes (correct)
  • 8 columns of 8 bytes

    • How many rounds does AES encryption undergo?

  • 9/11/13 rounds (correct)
  • 11 rounds
  • 13 rounds
  • 9 rounds

    • What is the key size for AES encryption?

    <p>128,192,256 bits</p> Signup and view all the answers

    What type of cipher is AES?

    <p>Symmetric encryption</p> Signup and view all the answers

    What is the last step in each round of AES encryption?

    <p>Add round key</p> Signup and view all the answers

    What is the purpose of the initial XOR key material in AES encryption?

    <p>To allow for fast XOR and table lookup implementation</p> Signup and view all the answers

    What is the primary advantage of AES over DES?

    <p>Improved security</p> Signup and view all the answers

    What is the output of the expansion 4-bit input into 8-bit output using the expansion key E/P?

    <p>[00111100]</p> Signup and view all the answers

    What is the purpose of the S-boxes in the DES algorithm?

    <p>Permutation and substitution</p> Signup and view all the answers

    How many S-boxes are used in the DES algorithm?

    <p>8</p> Signup and view all the answers

    What is the output of S-box #1 for the input (100010)?

    <p>(01)d = (0001)</p> Signup and view all the answers

    What is the purpose of the permutation in S-box #1?

    <p>To mix the bits of the input</p> Signup and view all the answers

    What is the input to S-box #1 in the example given?

    <p>(100010)</p> Signup and view all the answers

    What is the output of S-box #2 in the example given?

    <p>(01)d = (0001)</p> Signup and view all the answers

    What is the final output of the example?

    <p>(1101)</p> Signup and view all the answers

    What is the primary characteristic of block symmetric cipher principles, as described by Horst Feistel?

    <p>Structure dependent on key length, block size, and number of rounds</p> Signup and view all the answers

    What is the primary advantage of using a larger block size in symmetric encryption?

    <p>Greater security against cryptanalysis</p> Signup and view all the answers

    What is the primary advantage of using a larger key size in symmetric encryption?

    <p>Greater security against cryptanalysis</p> Signup and view all the answers

    What is the primary advantage of using multiple rounds in symmetric encryption?

    <p>Greater security against cryptanalysis</p> Signup and view all the answers

    What is the primary advantage of using a complex subkey generation algorithm?

    <p>Greater security against cryptanalysis</p> Signup and view all the answers

    What is the name of the algorithm referred to in the Data Encryption Standard (DES)?

    <p>Data Encryption Algorithm (DEA)</p> Signup and view all the answers

    When was the Data Encryption Standard (DES) published as a draft of the Federal Information Processing Standard (FIPS)?

    <p>March 1977</p> Signup and view all the answers

    Who published the request for proposals for a national symmetric-key cryptosystem in 1973?

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

    What was the main concern about the DES algorithm?

    <p>Use of a 56-bit key</p> Signup and view all the answers

    What did the Electronic Frontier Foundation (EFF) announce in 1998?

    <p>The breaking of a DES encryption</p> Signup and view all the answers

    What is the method of attack described by Diffie and Hellman?

    <p>Brute-force attack</p> Signup and view all the answers

    What is the estimated cost of a special-purpose computer proposed by the EFF?

    <p>$20 million</p> Signup and view all the answers

    What is the characteristic of the 2-Data Encryption Standard (2DES) algorithm?

    <p>Two encryption stages with two keys</p> Signup and view all the answers

    What has been the outcome of the controversy surrounding the DES algorithm?

    <p>The use of DES has flourished, especially in financial applications</p> Signup and view all the answers

    What is the main disadvantage of 2-DES?

    <p>It is susceptible to meet-in-the-middle attack</p> Signup and view all the answers

    What is the advantage of Triple DES over DES?

    <p>It has a longer key length</p> Signup and view all the answers

    What is the main reason why AES was developed?

    <p>To create a cipher that is resistant to brute-force attack</p> Signup and view all the answers

    What is the key size of Triple DES?

    <p>168 bits</p> Signup and view all the answers

    What is the block size of AES?

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

    What is the main advantage of AES over Triple DES?

    <p>AES is more secure than Triple DES</p> Signup and view all the answers

    What is the main design goal of AES?

    <p>To create a cipher that is resistant to brute-force attack</p> Signup and view all the answers

    What is the main characteristic of AES that makes it resistant to attacks?

    <p>Its iterative design</p> Signup and view all the answers

    What is the main advantage of AES over DES?

    <p>AES is more secure than DES</p> Signup and view all the answers

    What is the main reason why Triple DES is slower than AES?

    <p>It repeats the DES algorithm three times</p> Signup and view all the answers

    Study Notes

    AES Evaluation Criteria

    • Initial criteria: security, effort for practical cryptanalysis, cost in terms of computational efficiency, algorithm and implementation characteristics
    • Final criteria: general security, ease of software and hardware implementation

    AES Structure

    • Data block of 4 columns of 4 bytes is the state
    • Key is expanded to an array of words
    • AES has 9/11/13 rounds in which state undergoes:
      • Byte substitution (1 S-box used on every byte)
      • Shift rows (permute bytes between groups/columns)
      • Mix columns (subs using matrix multiply of groups)
      • Add round key (XOR state with key material)
    • Initial XOR key material and incomplete last round
    • Fast XOR and table lookup implementation

    AES Encryption Process

    • Symmetric encryption principles
    • Stream ciphers and RC4
    • Cryptography and cryptanalysis
    • Feistel cipher structure
    • Data encryption standard
    • Advanced encryption standard
    • Algorithm details
    • Key distribution

    Comparison of Symmetric Algorithms

    • AES, DES, and Triple DES
    • Plaintext block size: 128 bits
    • Ciphertext block size: 128 bits
    • Key size: 128, 192, or 256 bits

    DES General Structure

    • Symmetric-key block cipher
    • Adopted in 1977 by National Bureau of Standards (now NIST)
    • Algorithm is referred to as the Data Encryption Algorithm (DEA)
    • Minor variation of the Feistel network

    DES Design Controversy

    • Controversy over design, particularly in choice of 56-bit key
    • Subsequent events and public analysis show design was appropriate
    • Use of DES has flourished, especially in financial applications

    Meet-in-the-Middle Attack

    • Given a known pair (P,C), the attack proceeds as follows:
      • Encrypt all 256 possible values of K1, store results in a table
      • Decrypt C using all 256 possible values of K2
      • Check for matching between the two tables
    • Solution: Triple DES with two keys

    Triple DES (3DES)

    • Repeats basic DES algorithm three times using either two or three unique keys
    • First standardized for use in financial applications in ANSI standard X9.17 in 1985
    • Attractions:
      • 168-bit key length overcomes vulnerability to brute-force attack of DES
      • Underlying encryption algorithm is the same as in DES
    • Drawbacks:
      • Algorithm is sluggish in software
      • Uses a 64-bit block size

    Advanced Encryption Standard (AES) Origins

    • NIST issued a call for ciphers in 1997
    • 15 candidates were accepted in June 1998
    • 5 were shortlisted in August 1999
    • Rijndael was selected as the winner in November 2001

    Advanced Encryption Standard (AES)

    • Designed by Rijmen-Daemen in Belgium
    • Has 128/192/256-bit keys, 128-bit data
    • An iterative rather than Feistel cipher
    • Processes data as a block of 4 columns of 4 bytes (128 bits)
    • Operates on the entire data block in every round
    • Designed to be:
      • Resistant against known attacks
      • Speed and code compactness on many CPUs
      • Design simplicity

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    Description

    This quiz covers the design controversy and strength concerns of the Data Encryption Standard (DES) algorithm, its use in financial applications, and its legacy in modern systems.

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