Simple Python implementation of the Vigenère cipher. An article on this cipher appeared in the german c't-magazin 25/2023 p.154. An online version can be found on heise online.
- Python 3
There are a total of three parameters the program can take. d/e for decode or encode, followed by the text and the keyword:
python3 vigenere.py <d/e> <text> <keyword>
Note: The program removes all spaces and other characters from the text and turns it into one with only uppercase letters:
Windows users: On Windows you don't need to write python3 ..., python ... is enough.
To encrypt the text Lorem ipsum dolor sit with the keyword CTMAGAZIN, simply type:
python3 vigenere.py e "Lorem ipsum dolor sit" CTMAGAZIN
This will return NHDESIOAHOWALURRQG.
To decrypt the message NHDESIOAHOWALURRQG type:
python3 vigenere.py d NHDESIOAHOWALURRQG CTMAGAZIN
The output is LOREMIPSUMDOLORSIT.
You can modify the program to decrypt and encrypt whatever you like. You just need to remove .upper() from the line text = re.sub(f"[^{self.abc}]", "", text.upper()) and add letters to alphabet like that:
alphabet="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789,. '"
Now you can use more chars like shown in this example:
python3 vigenere.py e "Die c't ist dieses Jahr 40 geworden." CTMAGAZIN
Encoded: F1q i'EGvu KdoeDm5Acmhx P8Lix8oxd3vK
python3 vigenere.py d "F1q i'EGvu KdoeDm5Acmhx P8Lix8oxd3vK" CTMAGAZIN
Decoded: Die c't ist dieses Jahr 40 geworden.
kasiski.py contains a simple implementation of the Kasiksi-Examination. This Code is part of the article, that appeared on c't 28/2023 S. 142. An online version can be found on heise+.
By default, the Kasiski test only outputs the prime factors that are already sorted by frequency. You can insert the text directly on the command line (cipher) or read it from a file (-f FILE). If you also want to get an initial assessment using a simple frequency analysis, use -a.
python3 kasiski.py <-a> <cipher> [-f FILE]
Note: The analyse function works best with german texts. If the text is in another language, you must replace the letter (shift = (self.abc.index(letter) - self.abc.index("E")) % len(self.abc)) in the frequency analysis with the letter that appears most frequently in the other language.
Windows users: On Windows you don't need to write python3 ..., python ... is enough.
Example: If you want to obtain the factors for a cipher and then analyse possible key lengths, the command looks like this:
python3 kasiski.py -a GNVSYEIYLRLBNZQQXRUGYAQDYAUFNJMIWUMJGNVFGTMEYVUBHPWOLRAMIALFYEMKQVTIZHMODRLBHOCZBFBXVRVBCAMYYFWKXRZBWUQCZEMRHQAZBEMFVGLXHAUFNQQBMRVZBVNCLRVFHQMOARELYUVICPPBHNZQ
Factor 2 appeared 23 times
Factor 3 appeared 5 times
Factor 5 appeared 1 times
Factor 29 appeared 1 times
The key length is most likely 2, 3 or a product of that.
Which key length do you want to test? (Format: 3 5 15)2 4 6 8
Possible Key: IN
Possible Key: UNIX
Possible Key: INRBHN
Possible Key: CNIBUMMX
The key is UNIX. You can then decode the cipher with vigenère.py.
Copyright ©️ 2023 Wilhelm Drehling, Heise Medien GmbH & Co. KG
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.