etao 0.5.0

Simple cryptanalysis library

etao is a simple Python library that assists in the creation of cryptanalysis tools.

Installation

Install with pip:

pip install etao

Example Application

The following is a Caesar cipher solving tool that uses etao’s frequency analysis functions and built-in ciphers.

#!/usr/bin/env python
# Caesar cipher solver
import argparse
import etao


def main():
    parser = argparse.ArgumentParser(description="Caesar cipher solver")
    parser.add_argument('ciphertext', type=str, help='text to decipher')

    args = parser.parse_args()

    # Get every Caesar shift of the ciphertext
    shifts = [etao.caesar_shift(args.ciphertext, n) for n in range(26)]

    # Score each shift according to English character frequency.
    # Get tuples that pair the score with the text.
    scored_shifts = [(etao.score_text(shift), shift) for shift in shifts]

    # Sort by score, descending order
    scored_shifts.sort(reverse=True)

    # Print the top 3 results
    for result in scored_shifts[0:3]:
        print '"%s" (%02d%%)' % (result[1], int(result[0] * 100))

if __name__ == "__main__":
    main()

Here’s what it looks like in action:

$ ./caesar_solver.py "O GQFSOAWBU QCASG OQFCGG HVS GYM. WH VOG VODDSBSR PSTCFS, PIH HVSFS WG BCHVWBU HC QCADOFS WH HC BCK."
"A SCREAMING COMES ACROSS THE SKY. IT HAS HAPPENED BEFORE, BUT THERE IS NOTHING TO COMPARE IT TO NOW." (95%)
"L DNCPLXTYR NZXPD LNCZDD ESP DVJ. TE SLD SLAAPYPO MPQZCP, MFE ESPCP TD YZESTYR EZ NZXALCP TE EZ YZH." (65%)
"P HRGTPBXCV RDBTH PRGDHH IWT HZN. XI WPH WPEETCTS QTUDGT, QJI IWTGT XH CDIWXCV ID RDBEPGT XI ID CDL." (65%)