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

What type of cipher is AES?

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

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

<p>Add round key (D)</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 (B)</p> Signup and view all the answers

What is the primary advantage of AES over DES?

<p>Improved security (C)</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] (B)</p> Signup and view all the answers

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

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

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

<p>8 (D)</p> Signup and view all the answers

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

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

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

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

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

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

What is the final output of the example?

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

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

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

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

<p>Greater security against cryptanalysis (B)</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) (A)</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 (C)</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) (D)</p> Signup and view all the answers

What was the main concern about the DES algorithm?

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

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

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

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

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

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

<p>$20 million (C)</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 (D)</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 (C)</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 (C)</p> Signup and view all the answers

What is the advantage of Triple DES over DES?

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

What is the key size of Triple DES?

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

What is the block size of AES?

<p>128 bits (A)</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 (B)</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 (A)</p> Signup and view all the answers

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

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

What is the main advantage of AES over DES?

<p>AES is more secure than DES (D)</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 (B)</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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