What is the principle of DES encryption algorithm?

The Data Encryption Standard (DES) is a symmetric-key algorithm for the encryption of electronic data. Its principle is based on a Feistel network, which divides the input block into two halves and processes them alternately through a series of rounds, each involving substitution (S-boxes) and permutation operations.

Here's a simplified explanation:

1. Initial Permutation (IP): The plaintext block is first permuted according to a fixed table.
2. 16 Rounds: The block is then processed through 16 identical rounds. In each round:
   • Key Mixing: A subkey (derived from the main key) is XORed with one half of the block.
   • Substitution and Permutation: The result is passed through an S-box (substitution box) followed by a permutation.
   • Swap: The two halves of the block are swapped.
3. Final Permutation (FP): After the 16th round, the block undergoes a final permutation to produce the ciphertext.

Example:
Consider a plaintext block "11010110" and a key "10101010". The DES algorithm would perform the initial permutation, followed by 16 rounds of processing (each with its own subkey derived from the main key), and finally, the final permutation to produce the ciphertext.

Note: DES is now considered insecure for many applications due to its small key size (56 bits), making it vulnerable to brute-force attacks. It has been largely replaced by the Advanced Encryption Standard (AES).

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