From 7142c084ed1400c47164b93bd64bc132beca16a8 Mon Sep 17 00:00:00 2001
From: Deburama1 <debanjan1@hotmail.fr>
Date: Wed, 15 May 2024 22:03:59 -0400
Subject: [PATCH] finished assignement

---
 python/solution.py | 87 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)

diff --git a/python/solution.py b/python/solution.py
index e69de29..7b1ef8a 100644
--- a/python/solution.py
+++ b/python/solution.py
@@ -0,0 +1,87 @@
+def create_playfair_matrix(keyword):
+    # Generate a 5x5 matrix for the Playfair cipher using the keyword
+    matrix = []
+    seen = set()
+    keyword = "".join([char for char in keyword if not (char in seen or seen.add(char))])
+    alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"  # Note: J = I
+
+    # These are characters from the keyword that are inserted into the matrix
+    for char in keyword:
+        if char not in matrix:
+            matrix.append(char)
+
+    # add the remaining alphabet characters also into a matrix
+    for char in alphabet:
+        if char not in matrix:
+            matrix.append(char)
+
+    
+    return [matrix[i:i + 5] for i in range(0, len(matrix), 5)]
+
+
+def preprocess_text(ciphertext):
+    # Prepare the text by replacing J with I and forming digraphs
+    ciphertext = ciphertext.replace("J", "I")
+    pairs = []
+    i = 0
+
+    while i < len(ciphertext):
+        pair = ciphertext[i]
+        if i + 1 < len(ciphertext):
+            if ciphertext[i] == ciphertext[i + 1]:
+                pair += "X"
+                i += 1
+            else:
+                pair += ciphertext[i + 1]
+                i += 2
+        else:
+            pair += "X"
+            i += 1
+        pairs.append(pair)
+
+    return pairs
+
+
+def locate_char(char, matrix):
+    # This is used to find the position of the character inside the matrix
+    for row in range(5):
+        for col in range(5):
+            if matrix[row][col] == char:
+                return row, col
+    return None
+
+
+def playfair_decrypt(ciphertext, keyword):
+    # Here we decrypt the ciphertext using the Playfair cipher with a keyword
+    matrix = create_playfair_matrix(keyword)
+    pairs = preprocess_text(ciphertext)
+    decrypted_text = ""
+
+    for pair in pairs:
+        row1, col1 = locate_char(pair[0], matrix)
+        row2, col2 = locate_char(pair[1], matrix)
+
+        if row1 == row2:
+            decrypted_text += matrix[row1][(col1 - 1) % 5]
+            decrypted_text += matrix[row2][(col2 - 1) % 5]
+        elif col1 == col2:
+            decrypted_text += matrix[(row1 - 1) % 5][col1]
+            decrypted_text += matrix[(row2 - 1) % 5][col2]
+        else:
+            decrypted_text += matrix[row1][col2]
+            decrypted_text += matrix[row2][col1]
+
+    return decrypted_text
+
+
+# Here we encrypte the message and the key
+ciphertext = "IKEWENENXLNQLPZSLERUMRHEERYBOFNEINCHCV"
+keyword = "SUPERSPY"
+
+#test
+decrypted_text = playfair_decrypt(ciphertext, keyword)
+decrypted_text = decrypted_text.replace("X", "")
+
+#answer:
+print(decrypted_text)
+