Des Key Generation In Python
Nov 19, 2017 pydes. Basic but pure DES implementation in Python I 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. Data Encryption Standard is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page. Demonstrate the Data Encryption Standard. This is a pure python implementation of the DES encryption algorithm. It is in pure python to avoid portability issues, since most DES implementations are programmed in C (for performance reasons). Triple DES class is also implemented, utilising the DES base. Triple DES is either DES-EDE3 with a 24 byte key, or DES-EDE2 with a 16. Let's move on to the DES subkey generation, which takes a 56 bit key and then outputs 16 subkeys, each of which are 48 bits long. The diagram illustrates how the subkey generation works. PC blocks stand for permuted choice, and is a permutation and a compression block, where the outputs are shorter than the inputs.
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| Discusses symmetric encryption key generation techniques for block encryption algorithms such as AES, Blowfish, and Twofish, or for other algorithms such as ChaCha20.
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Multiple implementations of DES (Data Encryption Standard) encryption anddecryption. Includes the following:
- des.py
- Straightforward but slow. Well documented and easy to follow; a goodlearning tool for people new to DES.
- des.c
- Conversion of des.py into C.
- des_64.c
- Optimized based on techniques described below in the optimizationssection. Useful learning tool to understand these optimizations
- crack/
- Distributed, optimized key search (known plaintext attack). Takes a knownplaintext, ciphertext pair and tries every key until one of them works.More information in /crack/README.rst
All implementations except for crack/ are learning tools for DES andoptimizations. In contrast, crack/ is fully optimized and not meant forreadability, although it is well commented and as readable as it can be withoutsacrificing speed.
The software is licensed under the MIT license (see LICENSE.txt), so you canmodify and reuse this code without any restrictions. If you re-use a largepart of the code, attribution would be nice, but not required.
Contributions are welcome!
des.py
To encrypt, run des.py using Python and pass in your plaintext and key in hex:
Here, beefbeefbeefbeef is the plaintext and 0123456789abcdef is thekey. They both must be 16 hex digits.
To decrypt, use the -d option and give ciphertext instead of plaintext:
ASCII Input/Output
If you want to give the plaintext with 8 ASCII characters, use the -a option:
When decrypting, -a will instead convert the resulting plaintext into ASCII:
Verbose Output
You can also use the -v option to have it show detailed step by stepcalculations:
Use this for your homework!
des.c and des_64.c
You will need GNU Make and gcc. To compile, run make:
This will create executables des and des_64.
Des Key Generation In Python Download
For now, there is no way to provide input on the command line. Sorry, it's inthe TODO list. You will have to put the input in the code yourself. Currentlydes and des_64 are set up to run many encryptions as a speed test.
Optimizations
These optimizations were proposed by Eli Biham in the paper 'A Fast New DESImplementation in Software'.
64-Bit Parallel
This is a way to do 64 encryptions simultaneously utilizing 64-bit integers. Dungeon siege 2 deluxe cd key generator for games.
Consider the normal way to do 64 encryptions at once. We would store each key,plaintext and ciphertext in an array. Then, every time we do an operation, wedo it to all 64. Now consider how one of these values, the key for example, isstored. They would be stored in an array like this:
| Bit 1 | Bit 2 | Bit 3 | Bit 4 | Bit 5 | .. | |
| int64 Key 1 | a | b | c | d | e | .. |
| int64 Key 2 | f | g | h | i | j | .. |
| int64 Key 3 | k | l | m | n | o | .. |
| int64 Key 4 | p | q | r | s | t | .. |
| int64 Key 5 | u | v | w | x | y | .. |
| .. | .. | .. | .. | .. | .. | .. |
Each row contains a key. We can store each key as a 64-bit integer, so wewould have an array of 64 integers. Now suppose we transpose the table above:
| Key 1 | Key 2 | Key 3 | Key 4 | Key 5 | .. | |
| int64 Bit 1 | a | f | k | p | u | .. |
| int64 Bit 2 | b | g | l | q | v | .. |
| int64 Bit 3 | c | h | m | r | w | .. |
| int64 Bit 4 | d | i | n | s | x | .. |
| int64 Bit 5 | e | j | o | t | y | .. |
| .. | .. | .. | .. | .. | .. | .. |
We store each row in a 64-bit integer, again giving us an array of 64 integers.We call this zipped format. Now instead of looping through each of the 64parallel encryptions to do an operation, we can just do the operation on one64-bit integer. For example, Doing an xor with two elements of arrays in thisformat, a single xor instruction will simultaneously do an xor for all 64encryptions.
When you see functions like zip_64_bit in the code, these convert from normalto zipped format. Since this is like transposing a matrix, zip_64_bit is itsown inverse.
Permutation Elimination
Permutations are expensive and DES requires a lot of them. But we don'tactually have to permute things in memory in order to compute the result.Instead, we can index the bit that would be used if the permutation wereactually performed. Biham explains this as 'changing the naming of theregisters.' This includes the expansion step as well.
This is best explained by example. Consider this pseudocode:
It's pretty obvious the swap is unnecessary:
Eliminating permutations is the same idea on a larger scale.
Bitwise S-Boxes
Des Key Generation In Python List
Traditionally, s-boxes are implemented with lookup tables. But s-boxes canactually be implemented using nothing but logic gate operations, which is muchfaster, especially when using the 64-bit parallel optimization.
Finding the optimum logic design of s-boxes is very non-trivial. A Eli Bihamtalks about this in his paper 'A Fast New DES Implementation in Software', butMatthew Kwan's page entitled bitslicehas much more up to date information, as well as some history.
The fastest implementation I know about is implemented in John the Ripper. They actually havemultiple implementations, and the fastest one is automatically chosen.
This project's bitwise DES s-box implementation can be found ininclude/sbox.h, which defines functions s0 through s7. I didn't come upwith any designs myself.