From: Neil Smith <neil.git@njae.me.uk>
Date: Tue, 24 Jun 2014 14:54:48 +0000 (+0100)
Subject: Added hill-climbing for monoalphabetic substitution ciphers
X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=f23ebe9e009e465a31bd0aac2a9d9cd82da642f8;p=cipher-training.git

Added hill-climbing for monoalphabetic substitution ciphers
---

diff --git a/cipherbreak.py b/cipherbreak.py
index e89407c..eae56cf 100644
--- a/cipherbreak.py
+++ b/cipherbreak.py
@@ -2,6 +2,7 @@ import string
 import collections
 import norms
 import logging
+import random
 from itertools import zip_longest, cycle, permutations, starmap
 from segment import segment
 from multiprocessing import Pool
@@ -228,6 +229,51 @@ def column_transposition_break_mp(message, translist=transpositions,
         return max(breaks, key=lambda k: k[1])
 column_transposition_break = column_transposition_break_mp
 
+def monoalphabetic_break_hillclimbing(message, max_iterations = 10000000, 
+        fitness=Pletters):
+    ciphertext = unaccent(message).lower()
+    alphabet = list(string.ascii_lowercase)
+    random.shuffle(alphabet)
+    alphabet = ''.join(alphabet)
+    return monoalphabetic_break_hillclimbing_worker(ciphertext, alphabet,
+        max_iterations, fitness)
+
+def monoalphabetic_break_hillclimbing_mp(message, workers=100, 
+        max_iterations = 10000000, fitness=Pletters, chunksize=1):
+    worker_args = []
+    ciphertext = unaccent(message).lower()
+    for i in range(workers):
+        alphabet = list(string.ascii_lowercase)
+        random.shuffle(alphabet)
+        alphabet = ''.join(alphabet)
+        worker_args.append((ciphertext, alphabet, max_iterations, fitness))
+    with Pool() as pool:
+        breaks = pool.starmap(monoalphabetic_break_hillclimbing_worker,
+            worker_args, chunksize)
+    return max(breaks, key=lambda k: k[1])
+
+def monoalphabetic_break_hillclimbing_worker(message, alphabet, 
+        max_iterations, fitness):
+    def swap(letters, i, j):
+        if i > j:
+            i, j = j, i
+        if i == j:
+            return letters
+        else:
+            return letters[:i] + letters[j] + letters[i+1:j] + letters[i] + letters[j+1:]
+    best_alphabet = alphabet
+    best_fitness = float('-inf')
+    for i in range(max_iterations):
+        alphabet = swap(alphabet, random.randrange(26), random.randrange(26))
+        cipher_translation = ''.maketrans(string.ascii_lowercase, alphabet)
+        plaintext = message.translate(cipher_translation)
+        if fitness(plaintext) > best_fitness:
+            best_fitness = fitness(plaintext)
+            best_alphabet = alphabet
+            print(i, best_alphabet, best_fitness, plaintext)
+    return best_alphabet, best_fitness
+
+
 def column_transposition_break_worker(message, transposition, 
         fillcolumnwise, emptycolumnwise, fitness):
     plaintext = column_transposition_decipher(message, transposition,