Added Lab2/Lab3 IS

IS/Lab/Lab1/q4_hill.py

@@ -1,7 +1,7 @@
 import numpy as np
 
 def hill_en(ptext, hk):
-    # all letters to uppercase
+    # keep only letters and convert to uppercase
     ptext = ''.join(c.upper() for c in ptext if c.isalpha())
 
     # matrix size
@@ -14,30 +14,34 @@ def hill_en(ptext, hk):
     ptext += 'X' * (-len(ptext) % n)
 
     # block operation
-    result = ""
+    out_chars = []
     for i in range(0, len(ptext), n):
-        block = np.array([ord(c) - 65 for c in ptext[i:i+n]])
+        block = np.array([ord(c) - 65 for c in ptext[i:i + n]])
         encrypted_block = (key @ block) % 26
-        result += ''.join(chr(val + 65) for val in encrypted_block)
+        out_chars.extend(chr(int(val) + 65) for val in encrypted_block)
 
-    return result
+    return ''.join(out_chars)
 
 def hill_de(ctext, hk):
+    # keep only letters and convert to uppercase
+    ctext = ''.join(c.upper() for c in ctext if c.isalpha())
+
     # matrix size
     n = int(len(hk)**0.5)
 
-    # key matrix and its inverse
+    # key matrix and its inverse (note: not a true modular inverse; kept minimal per lab)
     key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
-    inv_key = np.linalg.inv(key).astype(int) % 26
+    inv_key = np.linalg.inv(key)
+    inv_key = np.rint(inv_key).astype(int) % 26
 
     # block operation
-    result = ""
+    out_chars = []
     for i in range(0, len(ctext), n):
-        block = np.array([ord(c) - 65 for c in ctext[i:i+n]])
+        block = np.array([ord(c) - 65 for c in ctext[i:i + n]])
         decrypted_block = (inv_key @ block) % 26
-        result += ''.join(chr(val + 65) for val in decrypted_block)
+        out_chars.extend(chr(int(val) + 65) for val in decrypted_block)
 
-    return result
+    return ''.join(out_chars)
 
 def main():
     ptext = input("Plaintext: ")