made test_break_vigenere.py

Author: nikos258

ciphers/break_vigenere.py

@@ -90,7 +90,7 @@ def friedman_method(ciphertext: str, max_keylength: int | None = None) -> int:
     page: https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher The algorithm
     is in the book "Introduction to Cryptography", K. Draziotis
     https://repository.kallipos.gr/handle/11419/8183
-    :param ciphertext: a string (text)
+    :param ciphertext: a string (uppercase text)
     :param max_keylength: the maximum length of key that Friedman's method
     should check, if None then it defaults to the length of the cipher
     :return: the length of the key
@@ -144,7 +144,7 @@ def find_key(ciphertext: str, key_length: int) -> str:
     to a letter of the key. The whole procedure takes place for every letter
     of the key (essentially as many times as the length of the key). See
     here: https://www.youtube.com/watch?v=LaWp_Kq0cKs
-    :param ciphertext: a string (text)
+    :param ciphertext: a string (uppercase text)
     :param key_length: a supposed length of the key
     :return: the key as a string
     """
@@ -190,7 +190,12 @@ 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.
+    IMPORTANT: Some trial and error might be needed to find the actual key
+    especially by changing the value of MAX_KEYLENGTH.
+
     """
+    # clean the ciphertext so that it only contains uppercase letters with no
+    # punctuation, spaces etc.
     clean_ciphertext_list = []
     for symbol in ciphertext.upper():
         if symbol in LETTERS:
@@ -208,15 +213,9 @@ def find_key_from_vigenere_cipher(ciphertext: str) -> str:
 
 
 if __name__ == "__main__":
-    print("")
+    print()
     # # how to execute
     # with open("out.txt") as file:
     #     ciphertext = file.read()
     #     key = find_key_from_vigenere_cipher(ciphertext)
     #     print(key)
-
-
-
-# ---------- TESTS ----------
-# def test_index_of_coincidence(f)
-

ciphers/test_break_vigenere.py

@@ -0,0 +1,48 @@
+import math
+
+from ciphers.break_vigenere import (
+    LETTER_FREQUENCIES_DICT,
+    calculate_indexes_of_coincidence,
+    find_key,
+    find_key_from_vigenere_cipher,
+    friedman_method,
+    get_frequencies,
+    index_of_coincidence,
+)
+
+
+class Test:
+    def test_index_of_coincidence(self):
+        ic = index_of_coincidence({"a": 50, "b": 50}, 50)
+        assert math.isclose(ic, 2.0)
+
+    def test_calculate_indexes_of_coincidence(self):
+        ciphertext = "hellothere"
+        result = calculate_indexes_of_coincidence(ciphertext, 2)
+        assert result == [0.1, 0.3]
+
+    def test_friedman_method(self):
+        ciphertext = "asqsfdybpypvhftnboexqumfsnglmcstyefv".upper()
+        result = friedman_method(ciphertext, 5)
+        assert result == 3
+
+    def test_get_frequencies(self):
+        result = get_frequencies()
+        expected = tuple(num / 100 for num in LETTER_FREQUENCIES_DICT.values())
+        assert result == expected
+
+    def test_find_key(self):
+        ciphertext = "asqsfdybpypvhftnboexqumfsnglmcstyefv".upper()
+        result = find_key(ciphertext, 3)
+        assert result == "ABC"
+
+    def test_find_key_from_vigenere_cipher(self):
+        ciphertext = (
+            "A dqxryeocqgj mpth ms sptusb ticq ms aoihv. Fgf "
+            "edrsou ylxmes jhv, sos exwyon uweqe igu msfjplxj "
+            "vbtliyy. Bno xme xqupi's b uwele, bpg eql ujh qjn bpg "
+            "atmfp piwema spfyftv. E wotg ec fnz qwljr ocpi bovng "
+            "wremn dw xwfgw."
+        )
+        result = find_key_from_vigenere_cipher(ciphertext)
+        assert result == "ABCDEF"