casper-guo/vigenere-cipher-demo

Demonstration of the Vigenere cipher and its decryption techniques for the MHacks lightning talk

A basic demostration of the Vigenere cipher and the Kasiski examination

The encrypt and decrypt files implement both Caesar and Vigenere cipher. utils.py implements a few helper functions that showcases key aspects of the Kasiski examination.

Both encrypt files require the following command line arguments in order:

• input-file: a text file.
• output-file: a text file to store the encrypted text. If it doesn't exist, it will be created.
• key: the encryption key for the Vigenere cipher or the offset for the Caesar cipher.

Both decrypt files require the following command line arguments in order:

• input-file: a text file.
• output-file: a text file to store the decrypted text. If it doesn't exist, it will be created.
• key: the encryption key for the Vigenere cipher or the offset for the Ceasar cipher.

utils.py contains the following helper functions:

• infer_key: given a segment of encrypted and correspoinding plain text, infer the encryption key.
• plot_frequency: given the encrypted document and a candidate key length, plot the letter distribution that is encrypted by each key letter.
• find_identical: find all repeated sequences of a certain length and return their beginning indices.