C-3 We now examine the elements of S-DES in more detail. C.2 S-DES Key Generation S-DES depends on the use of a 10-bit key shared between sender and receiver. From this key, two 8-bit subkeys are produced for use in particular stages of the encryption and decryption algorithm. Figure C.2 depicts the stages followed to produce the subkeys. (S)DES input/key complement property. P3.10 (a) Using input X' and key K', both inputs to the first XOR are complemented, therefore the XOR output, and the result of F, will be the same as using uncomplemented X and K The second XOR has inputs L' and F.
Basic but pure DES implementation in PythonI have written it for fun because nothing else.
How it works ?
Everything is made within a class called 'des'. This class can be instanciated once and used to cipher and decipher multiple datas.It also support padding using the PKCS5 specification. (So the data is padding even if it is multiple of 8 to be sure that the last byte il be padding data).The generation of all the keys used is made in the method generatekeys and substitute apply the SBOX permutation.The main method is run which is called by both encrypt and decrypt but in a different mode. This method do basically all the stuff, it loopthrought all the blocks and for each do the 16th rounds.
Be careful: This module implement DES in ECB mode, so you can't make it weaker. I didn't made it to be strong but for fun.
How to use it ?
I have not done any interface to take argument in command line so this module can't be used as a script. (feel free to modify it).To use it from python shell or in another module do:
Note: In this exemple no padding is specified so you have to provide a text which is multiple of 8 bytes. The key is cut to 8 bytes if longer.
Source Code In C++
To use padding: