Added Lab2/Lab3 IS

IS/Lab/Lab1/q5_john.py

@@ -2,20 +2,19 @@ def main():
     shift = (ord('C') - ord('y')) % 26
 
     ctext = "XVIEWYWI"
-    plaintext = ""
+    plaintext = []
 
-    for char in ctext:
-        if char.isalpha():
-            shifted = ord(char.lower()) - shift
-            if shifted < ord('a'):
-                shifted += 26
-            plaintext += chr(shifted)
+    for ch in ctext:
+        if ch.isalpha():
+            base = ord('a')
+            shifted = (ord(ch.lower()) - base - shift) % 26 + base
+            plaintext.append(chr(shifted))
         else:
-            plaintext += char
+            plaintext.append(ch)
 
     print(f"Attack type: Known plaintext attack")
     print(f"Ciphertext: {ctext}")
-    print(f"Decrypted: {plaintext}")
+    print(f"Decrypted: {''.join(plaintext)}")
 
 if __name__ == '__main__':
     main()