pre-commit 1

Author: nikos258

ciphers/break_vigenere.py

@@ -1,12 +1,36 @@
 LETTER_FREQUENCIES_DICT = {
-    'A': 8.12, 'B': 1.49, 'C': 2.71, 'D': 4.32, 'E': 12.02, 'F': 2.3, 'G': 2.03,
-    'H': 5.92, 'I': 7.31, 'J': 0.1, 'K': 0.69, 'L': 3.92, 'M': 2.61,
-    'N': 6.95, 'O': 7.68, 'P': 1.82, 'Q': 0.11, 'R': 6.02, 'S': 6.28,
-    'T': 9.10, 'U': 2.88, 'V': 1.11, 'W': 2.09, 'X': 0.17, 'Y': 2.11, 'Z': 0.07
+    "A": 8.12,
+    "B": 1.49,
+    "C": 2.71,
+    "D": 4.32,
+    "E": 12.02,
+    "F": 2.3,
+    "G": 2.03,
+    "H": 5.92,
+    "I": 7.31,
+    "J": 0.1,
+    "K": 0.69,
+    "L": 3.92,
+    "M": 2.61,
+    "N": 6.95,
+    "O": 7.68,
+    "P": 1.82,
+    "Q": 0.11,
+    "R": 6.02,
+    "S": 6.28,
+    "T": 9.10,
+    "U": 2.88,
+    "V": 1.11,
+    "W": 2.09,
+    "X": 0.17,
+    "Y": 2.11,
+    "Z": 0.07,
 }
 LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 PARAMETER = 0.0665  # index of confidence of the entire language (for english 0.0665)
-MAX_KEYLENGTH = None  # None is the default, you can also try a positive integer (example: 10)
+MAX_KEYLENGTH = (
+    None  # None is the default, you can also try a positive integer (example: 10)
+)
 
 
 def index_of_coincidence(frequencies: dict, length: int) -> float:
@@ -20,8 +44,8 @@ def index_of_coincidence(frequencies: dict, length: int) -> float:
     """
     index = 0.0
     for value in frequencies.values():
-        index += value * (value-1)
-    return index / (length * (length-1))
+        index += value * (value - 1)
+    return index / (length * (length - 1))
 
 
 def calculate_indexes_of_coincidence(ciphertext: str, step: int) -> list:
@@ -38,7 +62,7 @@ def calculate_indexes_of_coincidence(ciphertext: str, step: int) -> list:
 
     # for every starting point in [0, step)
     for j in range(step):
-        frequencies = dict()
+        frequencies = dict[str, int]
         c = 0
         for i in range(0 + j, length, step):
             c += 1
@@ -52,7 +76,7 @@ def calculate_indexes_of_coincidence(ciphertext: str, step: int) -> list:
     return indexes_of_coincidence
 
 
-def friedman_method(ciphertext: str, max_keylength: int=None) -> int:
+def friedman_method(ciphertext: str, max_keylength: int | None = None) -> int:
     """
     Implements Friedman's method for finding the length of the key of a Vigenere cipher. It finds the length with an
     index of confidence closer to that of an average text in the english language. Check the wikipedia page:
@@ -67,11 +91,12 @@ def friedman_method(ciphertext: str, max_keylength: int=None) -> int:
     if max_keylength is None:
         max_keylength = len(ciphertext)
 
-    frequencies = [1.5]  # the zeroth position should not be used: length of key is greater than zero
+    frequencies = [
+        1.5
+    ]  # the zeroth position should not be used: length of key is greater than zero
 
     # for every length of key
     for i in range(1, max_keylength + 1):
-
         # for a specific length it finds the minimum index of coincidence
         min1 = 15.0
         for val in calculate_indexes_of_coincidence(ciphertext, i):
@@ -90,7 +115,7 @@ def friedman_method(ciphertext: str, max_keylength: int=None) -> int:
 
 def get_frequencies() -> tuple:
     """Return the values of the global variable @LETTER_FREQUENCIES_DICT as a tuple ex. (0.25, 1.42, ...)."""
-    t = tuple(LETTER_FREQUENCIES_DICT[chr(i)] for i in range(ord('A'), ord('A') + 26))
+    t = tuple(LETTER_FREQUENCIES_DICT[chr(i)] for i in range(ord("A"), ord("A") + 26))
     return tuple(num / 100 for num in t)
 
 
@@ -107,7 +132,7 @@ def find_key(ciphertext: str, key_length: int) -> str:
     :param key_length: a supposed length of the key
     :return: the key as a string
     """
-    a = ord('A')
+    a = ord("A")
     cipher_length = len(ciphertext)
     alphabet_length = 26  # the length of the english alphabet
 
@@ -117,7 +142,7 @@ def find_key(ciphertext: str, key_length: int) -> str:
     for k in range(key_length):
         # find the frequencies of the letters in the message:
         # the frequency of 'A' is in the first position of the freq list and so on
-        freq = [0]*alphabet_length
+        freq = [0.0] * alphabet_length
         c = 0
         for i in range(k, cipher_length, key_length):
             freq[ord(ciphertext[i]) - a] += 1
@@ -131,7 +156,9 @@ def find_key(ciphertext: str, key_length: int) -> str:
             new_val = sum((freq[j] * real_freq[j]) for j in range(alphabet_length))
             if max1[0] < new_val:
                 max1 = [new_val, i]
-            freq.append(freq.pop(0))  # shift the list cyclically one position to the left
+            freq.append(
+                freq.pop(0)
+            )  # shift the list cyclically one position to the left
         key.append(max1[1])
 
     return "".join(chr(num + a) for num in key)  # return the key as a string
@@ -142,12 +169,12 @@ def find_key_from_vigenere_cipher(ciphertext: str) -> str:
     Tries to find the key length and then the actual key of a Vigenere ciphertext. It uses Friedman's method and
     statistical analysis. It works best for large pieces of text written in the english language.
     """
-    clean_ciphertext = list()
+    clean_ciphertext_list = list()
     for symbol in ciphertext.upper():
         if symbol in LETTERS:
-            clean_ciphertext.append(symbol)
+            clean_ciphertext_list.append(symbol)
 
-    clean_ciphertext = "".join(clean_ciphertext)
+    clean_ciphertext = "".join(clean_ciphertext_list)
 
     key_length = friedman_method(clean_ciphertext, max_keylength=MAX_KEYLENGTH)
     print(f"The length of the key is {key_length}")
@@ -158,7 +185,7 @@ def find_key_from_vigenere_cipher(ciphertext: str) -> str:
     return key
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     c = ""
     k = find_key_from_vigenere_cipher(c)
     print(k)