Podcast
Questions and Answers
How are the S-boxes in the function F represented in terms of input and output bits?
What are the two separate 32-bit quantities labeled in the single round of a Feistel cipher?
In a single round of the DES algorithm, what is the formula for Ri?
What is the role of S-boxes in the function F within a Feistel cipher?
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How are the overall processing at each round of a Feistel cipher summarized?
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What is the general structure of a single round in a Feistel cipher?
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What is the calculation of Li in a single round of the DES algorithm?
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How many bits does each S-box accept as input and produce as output?
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What is the function of the S-boxes in the function F within a Feistel cipher?
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What happens to the left and right halves of Ri-1 in a single round of DES processing?
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Study Notes
S-boxes in the Function F
- S-boxes transform a set of input bits into output bits through nonlinear mappings.
- Each S-box in DES accepts 6 input bits and produces 4 output bits.
Separate Quantities in a Feistel Cipher Round
- Two separate 32-bit quantities are labeled as Li and Ri during a single round.
- These quantities represent the left and right halves of the data block.
Formula for Ri in DES
- In a single round of DES, the formula for Ri is given as:
- Ri = Li-1 XOR F(Ri-1, Ki)
- Here, F denotes the function utilizing S-boxes and Ki represents the round key.
Role of S-boxes in Function F
- S-boxes provide confusion in the encryption process, enhancing security by nonlinearly mixing bits.
- They are vital for transforming the output of the function F to provide variability across rounds.
Overall Processing in Each Round of a Feistel Cipher
- Each round processes data by dividing it into two halves, applying a round function, and swapping the halves.
- The round function typically includes key mixing and S-box transformations.
General Structure of a Single Round in a Feistel Cipher
- A round consists of splitting the input into left (Li) and right (Ri) halves.
- The right half undergoes a round function, and the result is XORed with the left half, followed by a swap of left and right halves.
Calculation of Li in DES
- The calculation of Li in a single round of DES is:
- Li = Ri-1
- The left half in the next round takes on the current right half.
Impact on Left and Right Halves in DES Processing
- In DES, the left half Li becomes Ri-1 in the next round.
- The right half Ri undergoes the round function and is then combined with the left half via XOR operation.
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Description
Learn about the internal structure and calculations involved in a single round of the Data Encryption Standard (DES) algorithm, focusing on the left and right halves of each 64-bit intermediate value, and the formulas used in classic Feistel ciphers.
