How to add Python script to registry using Ctypes and kernel32.dll

Question

I'm trying to add my program to registry and this is my code...

def regc():
reg = windll.kernel32
print(reg)
hkey = 'HKEY_CURRENT_USER'
lsubkey = 'Software\Microsoft\Windows\CurrentVersion\Run'
reserved = 0
flag = 'REG_OPTION_BACKUP_RESTORE'
samdesired = 'KEY_ALL_ACCESS'
ipsec = None
handle = reg.RegCreateKeyExA(hkey, lsubkey, reserved, flag, samdesired, ipsec, None)

Its not giving me any errors but it still isn't creating a new key in registry. What am I doing wrong?

Answer 1

To use ctypes correctly, define .argtypes and .restype to do error checking of your parameters. Many of the types used are wrong. hkey , flag , and samdesired are not strings, for example. The return value is not a handle, but a status. The return value is an output parameter ( pkhResult in the docs). You must read the documentation and examine the header files of all the variable definitions carefully.

Also, in Python 3 strings are Unicode, so use the W form of Windows APIs to accept Unicode strings. Use raw strings ( r'...' ) for the subkey since it contains backslashes that could be interpreted as escape codes.

Here's a working example:

from ctypes import *
from ctypes import wintypes as w

# Values found from reading RegCreateKeyExW documentation,
# using Go To Definition on the types in Visual Studio,
# and printing constants in a C program, e.g. printf("%lx\n",KEY_ALL_ACCESS);

HKEY = c_void_p
PHKEY = POINTER(HKEY)
REGSAM = w.DWORD
LPSECURITY_ATTRIBUTES = c_void_p
LSTATUS = w.LONG

# Disposition values
REG_CREATED_NEW_KEY = 0x00000001
REG_OPENED_EXISTING_KEY = 0x00000002

ERROR_SUCCESS = 0

HKEY_CURRENT_USER = c_void_p(0x80000001)
REG_OPTION_NON_VOLATILE = 0
KEY_ALL_ACCESS = 0x000F003F

dll = WinDLL('kernel32')
dll.RegCreateKeyExW.argtypes = HKEY,w.LPCWSTR,w.DWORD,w.LPWSTR,w.DWORD,REGSAM,LPSECURITY_ATTRIBUTES,PHKEY,w.LPDWORD
dll.RegCreateKeyExW.restype = LSTATUS

hkey = HKEY_CURRENT_USER
lsubkey = r'Software\Microsoft\Windows\CurrentVersion\Run'
options = REG_OPTION_NON_VOLATILE
samdesired = KEY_ALL_ACCESS

# Storage for output parameters...pass by reference.
handle = HKEY()
disp = w.DWORD()

status = dll.RegCreateKeyExW(HKEY_CURRENT_USER, lsubkey, 0, None, options, samdesired, None, byref(handle), byref(disp))
if status == ERROR_SUCCESS:
    print(f'{disp=} {handle=}')

Output:

disp=c_ulong(2) handle=c_void_p(3460)

The disposition value of 2 indicates the key already exists ( REG_OPENED_EXISTING_KEY ).

You could also install pywin32 and use win32api.RegCreateKey or win32api.RegCreateKeyEx where all the work is already done for you.