New decoder added

python/solution.py

@@ -0,0 +1,51 @@
+def generate_playfair_square(passkey):
+    alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"
+    passkey = "SUPERY" #Duplicate letters are removed from the passkey (i.e. S and P)
+
+    square = []#creates the square for the playfair cipher
+    for char in passkey: 
+        if char not in square:
+            square.append(char)
+
+    for char in alphabet:
+        if char not in square:
+            square.append(char)
+
+    return [square[i * 5:(i + 1) * 5] for i in range(5)]
+
+def find_position(square, char):
+    for i, row in enumerate(square):
+        if char in row:
+            return (i, row.index(char))
+    return None
+
+def decrypt_pair(square, a, b):
+    row_a, col_a = find_position(square, a)
+    row_b, col_b = find_position(square, b)
+
+    if row_a == row_b:
+        return square[row_a][(col_a - 1) % 5] + square[row_b][(col_b - 1) % 5]
+    elif col_a == col_b:
+        return square[(row_a - 1) % 5][col_a] + square[(row_b - 1) % 5][col_b]
+    else:
+        return square[row_a][col_b] + square[row_b][col_a]
+
+def decrypt_playfair(ciphertext, passkey):
+    ciphertext = ciphertext.replace("J", "I")
+    square = generate_playfair_square(passkey)
+    plaintext = ""
+
+    for i in range(0, len(ciphertext), 2):
+        a = ciphertext[i]
+        b = ciphertext[i + 1]
+        plaintext += decrypt_pair(square, a, b)
+
+    return plaintext
+
+# Provided encrypted message and passkey
+ciphertext = "IKEWENENXLNQLPZSLERUMRHEERYBOFNEINCHCV"
+passkey = "SUPERY"
+
+# Decrypt the message
+decrypted_message = decrypt_playfair(ciphertext, passkey)
+print(decrypted_message)