Low-level Security Classes

If you have ever tried to do something simple like set a security descriptor for a Registry key you know what a pain the Win32 Security APIs can be. The process of initializing the various structures, allocating and deallocating memory and testing for error conditions is tedious and you end up with at least a page and a half of code which is difficult to read and doesn't lend itself to being reused next time you want to do the same thing. There had to be a better way, I thought. So I wrote a set of classes which take care of much of the donkey-work for you.

All of the classes correspond to the structures used by the low-level Security APIs - ACEs, ACLs, SIDs, TRUSTEEs, Security Descriptors. Their member functions are in most cases the same as the calls you would use when working with the API. The crucial differences are:

1. Often, a single constructor call is all that is needed to allocate and initialize an object
2. The classes which need to allocate memory will release it safely when the object goes out of scope.

Other than that, they are just thin wrappers. You can still get at the underlying objects if you need to, and you can also pass them to any of the API functions expecting a security object.

The best documentation I can give you is some sample code, so here is an example of how to create a secure Registry key which can be read by any user but only changed by administrators. To compare this with code which does the same thing using only API calls, see Setting a Security Descriptor for a new object in the MSDN library. Notice how much longer it is.

// Create a Registry key, granting KEY_READ access to everyone and 
// full control to the Administrators group.

// Initialize 2 EXPLICIT_ACCESS structures: 1 for Everyone,
// 1 for Administrators. 
CSid sidEveryone(CSid::WST_EVERYONE);
CSid sidAdmins(CSid::WST_LOCALADMINS);

CTrustee trEveryone(TRUSTEE_IS_WELL_KNOWN_GROUP, sidEveryone);
CTrustee trAdmins(TRUSTEE_IS_GROUP, sidAdmins);

EXPLICIT_ACCESS ea[2];

ea[0] = CExplicitAccess(KEY_READ, SET_ACCESS, NO_INHERITANCE, trEveryone);
ea[1] = CExplicitAccess(KEY_ALL_ACCESS, SET_ACCESS, NO_INHERITANCE, trAdmins);		

Note the constructor for CSid which allows you to create a SID for any of the well-known groups such as Administrators, ordinary users, etc.

// Create a new ACL and set the EA entries in it
CAcl acl;
if(acl.SetEntriesInAcl(2, ea) == ERROR_SUCCESS)
{

	// Initialize a security descriptor and add our ACL to it  
	CSecurityDescriptor sd;
	if(sd.SetSecurityDescriptorDacl(
		TRUE,     // fDaclPresent flag   
		acl, 
		FALSE))   // not a default DACL 
	{

		// Initialize a security attributes structure.
		CSecurityAttributes sa(sd, FALSE);

		// Use the security attributes to set the security descriptor 
		// when you create a key.
		DWORD	dwDisposition;
		HKEY	hKey;
 
		RegCreateKeyEx(HKEY_CURRENT_USER, "mykey1", 0, "", 0, 
			KEY_READ | KEY_WRITE, sa, &hKey, &dwDisposition); 

	}

}

That's it! If you have any suggestions or problems to report, post them here. There are plenty of ways this idea could be extended if you are of an inclination to do so.