MASI course asset "Sécurité des Applications". Topic on frequency analysis.
Install the requirements with the follwoing commands:
$ python -m venv venv
$ source venv/bin/activate
$ pip install -r requirements.txtAs stated in the documentation, the CLI has several options. You can visualize them by running the CLI with the following command :
$ python vernam.py --helpSeveral commands are available, with their batch of options. Please carefully read the docs before using.
--encrypt and --decrypt are not parameters in this version of the program.
Wich means you should use them with the -- !
The used command to validate the encryption feature is python vernam.py encrypt --in ./resources/input/encrypt/plain.txt --out ./resources/output/cipher.txt --key mykey.
The used command to validate the decryption feature is python vernam.py decrypt --in ./resources/input/decrypt/cipher.txt --out ./resources/output/plain.txt --key mykey.
The used command to validate the attack feature is python vernam.py attack --in ./resources/input/attack/cipher.txt --out ./resources/output/plain_attack.txt (the key was mykey, length of 5).
The used command to validate the attack feature with a bigger key is python vernam.py attack --in ./resources/input/attack/cipher_biggerkey.txt --out ./resources/output/plain_biggerkey.txt (the key was loremipsum, length of 10).
The used command to validate the attack feature with a bigger key is python vernam.py attack --in ./resources/input/attack/cipher_biggerkeytoo.txt --out ./resources/output/plain_biggerkeytoo.txt (the key was salutlesamis, length of 12).
Remark
We determined that bigger the text, bigger the key can be. But if we use a bigger key, the text must be bigger too otherwise the algorithm is gonna miscalculate the key thus resolving into unreadable plain text.
| Nom du fichier | Nom du fichier chiffré | Clé employée | Taille du texte (en caractères) | Taille de la clé (en caractères) | Résultat de l'attaque |
|---|---|---|---|---|---|
| plain.txt | cipher.txt | mykey | 2687 | 5 | OK |
| plain.txt | cipher_biggerkey.txt | loremipsum | 2687 | 10 | NOK (trouve 9/10 caractères de la clé) |
| plain.txt | cipher_biggerkeytoo.txt | salutlesamis | 2687 | 12 | NOK (trouve 9/12 caractères de la clé) |
| plain_biggest.txt | cipher_biggest.txt | mykey | 6634 | 5 | OK |
| plain_biggest.txt | cipher_biggest_biggerkey.txt | loremipsum | 6634 | 10 | OK |
| plain_biggest.txt | cipher_biggest_biggerkeytoo.txt | salutlesamis | 6634 | 12 | NOK (complètement) |
