Shopify Technical Challenge 2024 Playfair Cipher solver

python/solution.py

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+# Online Python Playground
+# Use the online IDE to write, edit & run your Python code
+# Create, edit & delete files online
+
+import string
+
+
+# function that creates the 5 by 5 matrix.
+def create_key_square(keyword):
+    alphabet = string.ascii_uppercase.replace(
+        'J', '')  # Capitalizes all the letters
+    key_square = []
+    used_letters = set()
+
+    ## adds the letters in the array
+    for char in keyword.upper():
+        if char not in used_letters and char in alphabet:
+            key_square.append(char)
+            used_letters.add(char)
+    ## adds the remaining letters in the alphabet
+    for char in alphabet:
+        if char not in used_letters:
+            key_square.append(char)
+
+    key_square_matrix = [key_square[i:i + 5] for i in range(0, 25, 5)]
+
+    return key_square_matrix
+
+
+# function that encrypts the message
+def preprocess_text(text):
+    text = text.upper().replace('J', 'I')
+    processed_text = ""
+
+    i = 0
+    ## loops through the text and adds the letters to the processed text
+    while i < len(text):
+        if text[i] in string.ascii_uppercase:
+            processed_text += text[i]
+            if i + 1 < len(text) and text[i] == text[i + 1]:
+                processed_text += 'X'
+            elif i + 1 < len(text) and text[i + 1] in string.ascii_uppercase:
+                processed_text += text[i + 1]
+                i += 1
+        i += 1
+
+    if len(processed_text) % 2 != 0:
+        processed_text += 'X'
+
+    return processed_text
+
+
+## finds the position of a character in the key square, returns the row and column of the character
+def find_position(key_square, char):
+    for row in range(5):
+        for col in range(5):
+            if key_square[row][col] == char:
+                return row, col
+    return None, None
+
+
+## finds the position of the two characters in the diagraph and then applies the playfair cypher rules
+## if same row then replace each char to its right
+## if same column then replace each char to its below
+## if neither then form a rectangle and replace each character in its row but the column of the other character.
+
+
+def encrypt_digraph(digraph, key_square):
+    row1, col1 = find_position(key_square, digraph[0])
+    row2, col2 = find_position(key_square, digraph[1])
+
+    if row1 is None or row2 is None or col1 is None or col2 is None:
+        raise ValueError("Invalid character in text")
+
+    if row1 == row2:
+        return key_square[row1][(col1 + 1) % 5] + key_square[row2][(col2 + 1) %
+                                                                   5]
+    elif col1 == col2:
+        return key_square[(row1 + 1) % 5][col1] + key_square[(row2 + 1) %
+                                                             5][col2]
+    else:
+        return key_square[row1][col2] + key_square[row2][col1]
+
+
+## finds the two characters in the digraph and then applies the playfair cypher rules
+## if same row then replace each char to its left
+## if same column then replace each char to above it
+## if neither then form a rectangle and replace each character in its row but the column of the other character.
+def decrypt_digraph(digraph, key_square):
+    row1, col1 = find_position(key_square, digraph[0])
+    row2, col2 = find_position(key_square, digraph[1])
+
+    if row1 is None or row2 is None or col1 is None or col2 is None:
+        raise ValueError("Invalid character in text")
+
+    if row1 == row2:
+        decrypted_pair = key_square[row1][(col1 - 1) %
+                                          5] + key_square[row2][(col2 - 1) % 5]
+    elif col1 == col2:
+        decrypted_pair = key_square[(row1 - 1) %
+                                    5][col1] + key_square[(row2 - 1) % 5][col2]
+    else:
+        decrypted_pair = key_square[row1][col2] + key_square[row2][col1]
+
+    return decrypted_pair
+
+
+##Creates the key square using the keywrod and then encrypts the message using the key square
+def playfair_cipher(text, keyword, encrypt=True):
+    key_square = create_key_square(keyword)
+    text = preprocess_text(text)
+    result = ""
+
+    for i in range(0, len(text), 2):
+        digraph = text[i:i + 2]
+        if encrypt:
+            result += encrypt_digraph(digraph, key_square)
+        else:
+            result += decrypt_digraph(digraph, key_square)
+
+    return result
+
+
+## After decrypting the text, it removes the x's and then returns the new text
+def remove_inserted_x(text):
+    result = ""
+    i = 0
+    while i < len(text):
+        if i < len(text) - 2 and text[i] == text[i + 2] and text[i + 1] == 'X':
+            result += text[i]
+            i += 2
+        else:
+            result += text[i]
+        i += 1
+
+    if result.endswith('X'):
+        result = result[:-1]
+
+    return result
+
+
+keyword = "SUPERSPY"
+ciphertext = "IKEWENENXLNQLPZSLERUMRHEERYBOFNEINCHCV"
+decryptedtext = playfair_cipher(ciphertext, keyword, encrypt=False)
+cleaned_text = remove_inserted_x(decryptedtext)
+
+print(cleaned_text)