vigenere_exploit_key_length

Exploitation of vigenere encryption with known key length

How to use

There is an english_freq variable, which means that the decrypted text must be in English. If you want to decipher a text in another language, you just have to change the letter frequency table

To launch the program you must execute the following command:

python3 exploit.py <key_length> <filename>

The decrypted text and the estimated key will appear in standard output

Exemple of use

I provided an example file with key length 5

python3 exploit.py 5 vigenere_01_ciphertext.txt
Estimated Key: house
Decrypted text: atleastthewhispergoessoourlastkingwhoseimageevenbutnowappeardtouswasasyouknowbyfortinbrasofnorwaytheretoprickdonbyamostemulatepridedaredtothecombatinwhichourvalianthamletforsothissideofourknownworldesteemdhimdidslaythisfortinbraswhobyasealdcompactwellratifiedbylawandheraldrydidforfeitwithhislifeallthosehislandswhichhestoodseizedoftotheconqueroragainstthewhichamoietycompetentwasgagedbyourkingwhichhadreturndtotheinheritanceoffortinbrashadhebeenvanquisherasbythesamecovenantandcarriageofthearticledesigndhisfelltohamletnowsiryoungfortinbrasofunimprovedmettlehotandfullhathintheskirtsofnorwayhereandtheresharkdupalistoflawlessresolutesforfoodanddiettosomeenterprisethathathastomachintwhichisnootherasitdothwellappearuntoourstatebuttorecoverofusbystronghandandtermscompulsatorythoseforesaidlandssobyhisfatherlostandthisitakeitisthemainmotiveofourpreparationsthesourceofthisourwatchandthechiefheadofthisposthasteandromageintheland

Limitations

The smaller the text, the more complicated the key estimation is, this is due to letter frequencies being distorted in small sentences.