added lab2 questions

IS/Lab/Lab2/3des.py

@@ -0,0 +1,31 @@
+from Crypto.Cipher import DES3
+from Crypto.Util.Padding import pad, unpad
+
+def des3_cipher(key):
+    return DES3.new(key.encode('utf-8'), DES3.MODE_ECB)
+
+def des3_en(ptext, key):
+    cipher = des3_cipher(key)
+    padded_text = pad(ptext.encode('utf-8'), DES3.block_size)
+    return cipher.encrypt(padded_text)
+
+def des3_de(ctext, key):
+    cipher = des3_cipher(key)
+    decrypted = unpad(cipher.decrypt(ctext), DES3.block_size)
+    return decrypted.decode('utf-8')
+
+def despad_key(key):
+    key = key.ljust(24)[:24]
+    return key
+
+def main():
+    print("Welcome to 3DES (Triple DES)")
+    ptext = input("Enter plaintext: ")
+    key = input("Enter key (minimum 16 characters for 3DES): ")
+    key = despad_key(key)
+    ctext = des3_en(ptext, key)
+    print("Your ciphertext: ", ctext)
+    print("Your decrypted plaintext: ", des3_de(ctext, key))
+
+if __name__ == '__main__':
+    main()