How to get/find domain sid from machine sid

Question

I can get machine Sid like below:

var dir = new DirectoryEntry($"WinNT://{Environment.MachineName},Computer");
var objSid = dir.Children.Cast<DirectoryEntry>().First().InvokeGet("objectSID");
var secId = new SecurityIdentifier((byte[])objSid, 0);
var machineSid = secId.AccountDomainSid.ToString();

I tried to find computer Sid from machine Sid but it is always NULL.

using (PrincipalContext principalContext = new PrincipalContext(ContextType.Domain, "AbcDomain", "userName", "password"))
{
    var pc01 = ComputerPrincipal.FindByIdentity(principalContext, IdentityType.Sid, machineSid);
    //output: pc01 = null
    var pc02 = ComputerPrincipal.FindByIdentity(principalContext, IdentityType.Name, "PC-JACKML5291");
    //output: pc02...

}

I want to check duplicate machine sid before calling JoinDomainOrWorkgroup . Can I get the Computer SID (joined domain) from machine SID?

Answer 1

The machine SID is not the same as the SID of the computer object on the domain. They are different.

According to this article ,

in order to assure uniqueness, the SID that Setup generates has one fixed subauthority value (21) and three randomly-generated subauthority values (the numbers following “S-1-5-21” in the output).

If you want the SID of the computer object on the domain, you will have to search for the object by the computer name.