Some lua tools for vigenere encryption, decryption and brute-force.
Based on the basic Blaise de Vigenère algorithm.

Vigenère cipher is a enhancement of Caesar's cipher. This is a substitution encryption technique as plain text letters are replaced by some fixed number of positions down the alphabet.
To implement it we need a plain-text and a key. Assuming the text is Vigenere and the key is lua . We map every alphabet character to its position :

a = 0, b = 1, c = 2, [...] z = 25

and we repeatedly add the key values to our plain text :

VIGENERE
LUALUALU
||||||||
GCGPHECY

Encoded text is GCGPHECY.

Required libraries :

• lua (tested on 5.1.5)

Clone the repository

git clone https://github.com/raymas/Vigenere.git

Four functions are implemented : three for a ciphertext-only attack, one for encryption.

You have three operation mode for this script :

• e for encryption
• d for decryption
• c for cracking

lua vigenere.lua [e|d|c]

Each modes have their specific arguments

Encryption 'e'

Options

--raw [text on cli]
--file [path to file]

The last argument should always be the key!

Usage : lua vigenere e --file plaintext.txt mysecretkey

Decryption 'd'

Options

--raw [text on cli]
--file [path to file]

The last argument should always be the key!

Usage : lua vigenere d --file ciphertext.txt mysecretkey

Crack 'c'

Options required either one or the other.

--raw [text on cli]
--file [path to file]

Options optional either one or the other.

--maxkeylength [integer of maximum key length by default it is 20]
--trylength [minimum length:maximum length]

The --maxkeylength argument try to guess the key with a maximum number of characters.

--trylength [lower:upper] output a key guesses from lower to upper bounds.

Usage example :

lua vigenere c --file ciphertext.txt --maxkeylength 12
lua vigenere c --file ciphertext.txt --trylength [1:20]

Brute force

keylengthguess(text, language, maxkeylength, verbose)
guessingKey(text, language, keylength, verbose)
decrypt(text, key, language)

You can use the three function to try a brute force decryption.

Firstly, we have to guess the key length using a frequency analysis of every letter in the encrypted text. It works better with long text as the key is repeating multiple times.

Secondly, we have to guess the key based on block chain and a frequency analysis for each character of the key.

Thirdly, we try a decryption with key that we just guess.

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us.

• raymas - Initial work - raymas

See also the list of contributors who participated in this project.

This project is licensed under the GNU 3.0 License - see the LICENSE.md file for details