C implementation of Data Encryption Standard algorithm.

The Data Encryption Standard (DES) is a block cipher (a form of shared secret encryption) that was selected by the National Bureau of Standards as an official Federal Information Processing Standard (FIPS) for the United States in 1976 and which has 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 easy understanding of the algorithm. Padding scheme used in this implementation is [PKCS5]

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

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

1. Generate a keyfile using:

   run_des.o -g /tmp/keyfile.key

2. Encrypt sample.txt using:

   run_des.o -e /tmp/keyfile.key /home/user/sample.txt /home/user/sample.enc

3. Decrypt sample.txt using:

   run_des.o -d /tmp/keyfile.key /home/user/sample.enc /home/user/sample_decrypted.txt

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

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:

   run_des.o -g /tmp/keyfile1.key
   run_des.o -g /tmp/keyfile2.key
   run_des.o -g /tmp/keyfile3.key

2. Encrypt using:

   run_des.o -e /tmp/keyfile1.key /home/user/sample.txt /home/user/sample.enc1
   run_des.o -e /tmp/keyfile2.key /home/user/sample.enc1 /home/user/sample.enc2
   run_des.o -e /tmp/keyfile3.key /home/user/sample.enc2 /home/user/sample.enc3

3. Decrypt using:

   run_des.o -d /tmp/keyfile3.key /home/user/sample.enc3 /home/user/sample.dec3
   run_des.o -d /tmp/keyfile2.key /home/user/sample.dec3 /home/user/sample.dec2
   run_des.o -d /tmp/keyfile1.key /home/user/sample.dec2 /home/user/sample_decrypted.txt

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