Feistel Cipher Structure Quiz and Flashcards

What is the main advantage of using a Feistel cipher structure?

What is the purpose of the concept of 'Diffusion' in the Feistel cipher?

What is the purpose of the concept of 'Confusion' in the Feistel cipher?

What is the purpose of creating 16 subkeys, each 48-bits long, in the DES algorithm?

Which of the following is NOT a key property of the Feistel cipher structure?

What is the purpose of the PC-1 permutation table?

What is the value of $C_4$ in the solution?

What is the value of $D_4$ in the solution?

What is the final value of the 56-bit key $K_4$?

What is the purpose of the circular left shift operation on the key in the DES algorithm?

Feistel Cipher

A symmetric structure used in constructing block ciphers, also known as a Feistel network.
Offers the advantage of similar encryption and decryption operations, requiring only a reversal of the key schedule.
Reduces the size of the code or circuitry required to implement the cipher by nearly half.

Feistel's Proposal

Utilizes a cipher that alternates between substitutions and permutations.
Implements diffusion and confusion to hide relationships between the ciphertext and plaintext, and the ciphertext and encryption key.

Diffusion

Hides the relationship between the ciphertext and plaintext by making each symbol in the ciphertext dependent on some or all symbols in the plaintext.
A single change in the plaintext will result in multiple changes in the ciphertext.

Confusion

Hides the relationship between the ciphertext and encryption key by making most or all bits in the ciphertext change when a single bit in the key is changed.

Data Encryption Standard (DES)

A block cipher that uses the Feistel structure.

How DES Works

The 64-bit key is permuted according to the PC-1 table to create 16 subkeys, each 48-bits long.
The subkeys are used in the encryption and decryption process.

Example: Key Generation

A hexadecimal key K = 133457799BBCDFF1 is converted to a binary key.
The binary key is permuted according to the PC-1 table to create 16 subkeys.
Each subkey is 48-bits long.

Learn about the symmetric structure used in the construction of block ciphers known as a Feistel network. Discover how encryption and decryption operations are similar, requiring a reversal of the key schedule. Explore Feistel's proposal of alternating substitutions and permutations in ciphers.