How the Data encryption standard (DES) algorithm work

Data encryption standard (DES) Algorithm

·       In a word, DES encryption encrypts plaintext data by breaking it down into smaller chunks (64-bit blocks) and using a cryptographic key to decrypt it. Essentially, it takes your legible message and changes it, block by block, into incomprehensible gibberish that can only be decrypted by the holder of the decryption key.

·       To put it another way, DES takes 64-bit plain text and converts it to a 64-bit ciphertext. Because we're dealing with asymmetric methods, the same key is utilized to decode the text as well.

 

The following are the steps in the algorithm process:

1. The 64-bit plain text block is passed to an initial permutation (IP) function to begin the process.

2. The plain text is subsequently subjected to the initial permutation (IP).

3. Following that, the initial permutation (IP) divides the permuted block into two halves, referred to as Left Plain Text (LPT) and Right Plain Text (RPT).

4. The encryption operation is repeated 16 times for each LPT and RPT.

5. Finally, the LPT and RPT are reunited, and the newly combined block is subjected to a Final Permutation (FP).    

6. As a result of this procedure, the desired 64-bit ciphertext is generated

The encryption process step (step 4, above) is further broken down into five stages:

1. Key transformation

2. Expansion permutation

3. S-Box permutation

4. P-Box permutation

5. XOR and swap

We apply the identical procedure for decryption, but we reverse the order of the 16 round keys.