How can I read 64-bit registry key from a 32-bit process?

Question

I\'ve been using the value of key MachineGuid from HKEY_LOCAL_MACHINE\\Software\\Microsoft\\Cryptography to uniquely identify hosts, but from 32-b

Answer 1

I would suggest you use the IsWow64Process() function to know when you are a 32-process running on a 64-bit OS, and then only apply the KEY_WOW64_64KEY flags in that specific condition. If the app is a 32-bit process on a 32-bit OS, or a 64-bit process on a 64-bit OS, the flags is not needed.

For example:

const 
  KEY_WOW64_64KEY = $0100; 
var 
  key: HKEY; 
  str: string; 
  len: DWORD; 
  flag: REGSAM;
  wow64: BOOL;
begin 
  flag := 0;
  wow64 := 0;
  IsWow64Process(GetCurrentProcess(), @wow64);
  if wow64 <> 0 then flag := KEY_WOW64_64KEY;

  if RegOpenKeyEx(HKEY_LOCAL_MACHINE, 'Software\Microsoft\Cryptography', 0, KEY_QUERY_VALUE or flag, key) = ERROR_SUCCESS then 
  try
    SetLength(str, 40); 
    len := Length(str) * SizeOf(Char); 
    if RegQueryValueEx(key, 'MachineGuid', nil, nil, PByte(Pointer(s)), @len) <> ERROR_SUCCESS then len := 0;
    SetLength(str, len div SizeOf(Char)); 
  finally
    RegCloseKey(key); 
  end; 
end;