Modified Lab 1 IS

IS/Lab/Lab1/q4_hill.py

@@ -1,18 +1,50 @@
-def hill_en(ptext,hk):
+import numpy as np
 
-def hill_de(ptext,hk):
+def hill_en(ptext, hk):
+    # all letters to uppercase
+    ptext = ''.join(c.upper() for c in ptext if c.isalpha())
+
+    # matrix size
+    n = int(len(hk)**0.5)
+
+    # key matrix
+    key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
+
+    # padding
+    ptext += 'X' * (-len(ptext) % n)
+
+    # block operation
+    result = ""
+    for i in range(0, len(ptext), 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)
+
+    return result
+
+def hill_de(ctext, hk):
+    # matrix size
+    n = int(len(hk)**0.5)
+
+    # key matrix and its inverse
+    key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
+    inv_key = np.linalg.inv(key).astype(int) % 26
+
+    # block operation
+    result = ""
+    for i in range(0, len(ctext), 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)
+
+    return result
 
 def main():
-    ptext = input("Kindly enter your desired plaintext: ")
-    hk = input("Kindly enter the Hill Key: ")
-
-    print("Welcome to the Hill cipher.")
-    print("Plaintext: ", ptext)
-    print("Hill Key: ", hk)
+    ptext = input("Plaintext: ")
+    hk = input("Hill Key: ")
     ctext = hill_en(ptext, hk)
-    print("Ciphertext: ", ctext)
-    decrypted_text = hill_de(ctext, hk)
-    print("Decrypted Text: ", decrypted_text)
+    print(f"Ciphertext: {ctext}")
+    print(f"Decrypted: {hill_de(ctext, hk)}")
 
 if __name__ == '__main__':
-    main()
+    main()