Des Key Generation Code In C

Posted By admin On 13.12.20

C implementation of Data Encryption Standard algorithm.

Jul 05, 2010 Using the Code Step 1: S-DES Key Generation. S-DES depends on the use of a 10-bit key shared between the sender and the receiver. From this key, two 8-bit subkeys are produced for use in particular stages of the encryption and decryption algorithm. The above figure depicts the stages followed to produce the subkeys. Generating DES Subkeys from 64b Master Key. Trying to generate DES sub-keys from master key. I have this so far. Not sure why it produces incorrect results. I have looked over everything and I'm pretty sure I have the right idea, although this is a difficult thing to tst for correctness. Trying to generate DES sub-keys from master key. I have this so far. Not sure why it produces incorrect results. I have looked over everything and I'm pretty sure I have the right idea, although this is a difficult thing to tst for correctness.

Overview

DES Weak Keys. DES uses 16 48-bits keys generated from a master 56-bit key (64 bits if we consider also parity bits). Weak keys: keys make the same sub-key to be generated in more than one round. Result: reduce cipher complexity. Weak keys can be avoided at key generation. Dmg 11. DES has 4 weak keys – 0100101 – FEFEFEFE.

Des Key Generation Code In C

The Data Encryption Standard (DES) is a block cipher (a form of shared secret encryption) that was selected by the NationalBureau of Standards as an official Federal Information Processing Standard (FIPS) for the United States in 1976 and whichhas subsequently enjoyed widespread use internationally. It is based on a symmetric-key algorithm that uses a 56-bit key.

This implementation of DES is not optimized in any way. The code has been written to provide readability and easyunderstanding of the algorithm. Padding scheme used in this implementation is [PKCS5]

S-des Key Generation Code In C

Compilation & Installation

This implementation has only been tested on Unix platform. But you may be able to compile/ run it on Windows.

  1. Make sure des.c, des.h and run_des.c are in the same directory
  2. Compile using: gcc -O3 des.c run_des.c -o run_des.o

Usage

Say we want to encrypt/ decrypt a file named /home/user/sample.txt

  1. Generate a keyfile using:

  2. Encrypt sample.txt using:

  3. Decrypt sample.txt using:

Don't lose the key file! you won't be able to decrypt an encrypted if you lose the keyfile.

More

Des Key Generation Program In C

DES is provided for educational purposes only. Do not use for any other reason.It has been implemented after J. Orlin Grabbe's DES Algorithm Illustrated

It is possible to use this implementation to facilitate TripleDES encryption process:

  1. Generate keys using:

  2. Encrypt using:

  3. Decrypt using:

The primary repository for DES is located at: http://github.com/tarequeh/DES/ The blog postdiscussing the implementation can be found at: CodeXNThis implementation of DES was written by Tareque Hossain

  • Cryptography Tutorial
  • Cryptography Useful Resources
  • Selected Reading

The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).

DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). General Structure of DES is depicted in the following illustration −

Since DES is based on the Feistel Cipher, all that is required to specify DES is −

  • Round function
  • Key schedule
  • Any additional processing − Initial and final permutation

Initial and Final Permutation

The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. The initial and final permutations are shown as follows −

Key

Round Function

The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.

  • Expansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first need to expand right input to 48 bits. Permutation logic is graphically depicted in the following illustration −

  • The graphically depicted permutation logic is generally described as table in DES specification illustrated as shown −

  • XOR (Whitener). − After the expansion permutation, DES does XOR operation on the expanded right section and the round key. The round key is used only in this operation.

  • Substitution Boxes. − The S-boxes carry out the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. Refer the following illustration −

  • The S-box rule is illustrated below −

Des Key Generation Code In C D

  • There are a total of eight S-box tables. The output of all eight s-boxes is then combined in to 32 bit section.

  • Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight permutation with rule shown in the following illustration:

Key Generation

The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration −

The logic for Parity drop, shifting, and Compression P-box is given in the DES description.

DES Analysis

The DES satisfies both the desired properties of block cipher. These two properties make cipher very strong.

  • Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.

  • Completeness − Each bit of ciphertext depends on many bits of plaintext.

During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. These keys shall be avoided.

Source Code In C++

DES has proved to be a very well designed block cipher. There have been no significant cryptanalytic attacks on DES other than exhaustive key search.