Update vigenere.py

Author: ELAMOURY

Algorithms/cryptology/vigenere_cipher/vigenere.py

@@ -10,7 +10,8 @@
 *  2019-11-07 Initial programming
 
 """
-
+import re
+from collections import Counter
 
 alphabet = "abcdefghijklmnopqrstuvwxyz "
 
@@ -49,16 +50,48 @@ def decrypt(cipher, key):
 
     return decrypted
 
+# Nettoyage et préparation du texte
+def clean_text(text):
+    return re.sub(r'[^a-z]', '', text.lower())
+
+# Index de Coïncidence
+def index_of_coincidence(text):
+    N = len(text)
+    freqs = Counter(text)
+    return sum(f * (f - 1) for f in freqs.values()) / (N * (N - 1)) if N > 1 else 0
+
+# Estimation de la longueur de la clé
+def estimate_key_length(text, max_len=20):
+    ic_scores = []
+    for key_len in range(1, max_len + 1):
+        groups = [text[i::key_len] for i in range(key_len)]
+        avg_ic = sum(index_of_coincidence(group) for group in groups) / key_len
+        ic_scores.append((key_len, avg_ic))
+    likely_lengths = sorted(ic_scores, key=lambda x: -x[1])
+    return likely_lengths[0][0]
+
+# Déduire la clé par fréquence
+def deduce_key(text, key_len):
+    alphabet = "abcdefghijklmnopqrstuvwxyz"
+    letter_to_index = {ch: idx for idx, ch in enumerate(alphabet)}
+    index_to_letter = {idx: ch for idx, ch in enumerate(alphabet)}
+    key = ''
+
+    for i in range(key_len):
+        group = text[i::key_len]
+        freq = Counter(group)
+        most_common = freq.most_common(1)[0][0]
+        shift = (letter_to_index[most_common] - letter_to_index['e']) % 26
+        key += index_to_letter[shift]
+    return key
 
 def main():
-    message = "i loove peanuts"
-    key = "banana"
+    message = "gagoclcqgzhzkwnqadgvvqbxtmnqgugczdcgjmumweuqsgirrceqffpxtugipbtqrvwfhqimntgfguwvnujvgaqggccugzogglwzognivugwgugzhtqurxsxriugbvritazipmvmwkgkjmbkgmkxgkcxcusrvbqggfpvgzhiplcuhhwmeqggqcrewitmigzmgzuhcznmuqhgquoqzfkvvmwrutgepiwqvedvgvcusevcpqgspwtuhvtiwciiuipeiegkjarepanmwiowtfsxktuqasnikfeygtgehvpmddswhcuesevlwzbskzkzqfpvwqdekauudrttgedswauusigaxazepbgerlepcdpspinaiifqrmfhgaimnhwqrqgekmpfglttgemiwfnqgdgkjqghganmaggauaiwnmwdgtjirqoyzlgfcznmoqhentkcivpgoqhxcqgzhhwmfqgtqqpfgiqciqoxtmuabeglkehmpowmwktqgzzevikxzvuwwhfekboabkcqvmwruqsgiegtcduiepgywegmrxoxgmvapckywqcyniugwvfmfullkdgdgrwzcuheoiueslpmpgwxrzqrcefmfqgjqzoqgjrmeffenmuemriqvmwipbnqgcwmwdgtgzfgsjnikegekmpfsevzghcmtcpqffplggfhgpczqygcpnfeuvqgslzcpqhivmxuccgvvqpetjqgwcnmgocqomraiiwvedwqgxcdtfkagzgifmvmqycvvximuikqbkfmunzseafqvfwqnxshgarmbjgbfqgetmvqgstcuciiompfocncoqghwvtqtcgbfqqvkavmzgwqufcyvzgfcddikfoypwkdzvuzkhspcqpqgkcxcusrviidoefaeaituaqgfuuqnzmexikfdcwasgspgpcxskgugzhhgarawktqpqgpgotauegugzhhgogzsvvlgroxkowqgfwanmdiuipfsltlgxomtmv "
+    key = deduce_key(message, 5)
     encrypted_message = encrypt(message, key)
     decrypted_message = decrypt(encrypted_message, key)
 
-    print("Original message: " + message)
-    print("Encrypted message: " + encrypted_message)
-    print("Decrypted message: " + decrypted_message)
-
+  
+   print("key: " + key)
 
 main()