Probabilistic ROT-n cracker

rot_n_cracker.py

#!/usr/bin/python
# wordlist.txt is a tab-delimited word frequency list.
# A list for the German language can be found here:
# https://github.com/gambolputty/dewiki-wordrank

import sys
import re
from collections import Counter
from string import ascii_lowercase as letters

MAXWORDS = 10000

text = open(sys.argv[1]).read().lower()
wordcount = Counter(re.findall(r'[a-z]+', text))

wordfreq = {}
for i, line in enumerate(open('wordlist.txt')):
    if i == MAXWORDS:
        break
    word, count = line.split()
    word = word.replace('ä', 'ae').replace('ö', 'oe').replace('ü', 'ue').replace('ß', 'ss')
    if re.match(r'^[a-z]+$', word):
        wordfreq[word] = int(count)

score = {n: 0 for n in range(1, 26)}
for shift in score:
    rot = str.maketrans(letters, (letters*2)[shift:shift+26])
    for word, freq in wordfreq.items():
        count = wordcount[word.translate(rot)]
        if count:
            score[shift] += count * freq

winner = max(score, key=score.get)
backrot = str.maketrans(letters, (letters*2)[26-winner:26+26-winner])
print(text.translate(backrot))