Convert a username to a SID string in C#/.NET

Question

There's a question about converting from a SID to an account name; there isn't one for the other way around.

How do you convert a username to a SID string, for example, to find out which HKEY_USERS subkey relates to a user of a given name?

Answer 1

The podcast tells me I should ask, and answer, questions when they're not answered on SO already. Here goes.

The easy way, with .NET 2.0 and up, is this:

NTAccount f = new NTAccount("username"); SecurityIdentifier s = (SecurityIdentifier) f.Translate(typeof(SecurityIdentifier)); String sidString = s.ToString(); 

The hard way, which works when that won't, and works on .NET 1.1 also:

[DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError=true)] public static extern bool LookupAccountName([In,MarshalAs(UnmanagedType.LPTStr)] string systemName, [In,MarshalAs(UnmanagedType.LPTStr)] string accountName, IntPtr sid, ref int cbSid, StringBuilder referencedDomainName, ref int cbReferencedDomainName, out int use);  [DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError=true)] internal static extern bool ConvertSidToStringSid(IntPtr sid, [In,Out,MarshalAs(UnmanagedType.LPTStr)] ref string pStringSid);   /// <summary>The method converts object name (user, group) into SID string.</summary> /// <param name="name">Object name in form domain\object_name.</param> /// <returns>SID string.</returns> public static string GetSid(string name) {     IntPtr _sid = IntPtr.Zero; //pointer to binary form of SID string.     int _sidLength = 0;   //size of SID buffer.     int _domainLength = 0;  //size of domain name buffer.     int _use;     //type of object.     StringBuilder _domain = new StringBuilder(); //stringBuilder for domain name.     int _error = 0;     string _sidString = "";      //first call of the function only returns the sizes of buffers (SDI, domain name)     LookupAccountName(null, name, _sid, ref _sidLength, _domain, ref _domainLength, out _use);     _error = Marshal.GetLastWin32Error();      if (_error != 122) //error 122 (The data area passed to a system call is too small) - normal behaviour.     {         throw (new Exception(new Win32Exception(_error).Message));     } else {         _domain = new StringBuilder(_domainLength); //allocates memory for domain name         _sid = Marshal.AllocHGlobal(_sidLength); //allocates memory for SID         bool _rc = LookupAccountName(null, name, _sid, ref _sidLength, _domain, ref _domainLength, out _use);          if (_rc == false) {             _error = Marshal.GetLastWin32Error();             Marshal.FreeHGlobal(_sid);             throw (new Exception(new Win32Exception(_error).Message));         } else {             // converts binary SID into string             _rc = ConvertSidToStringSid(_sid, ref _sidString);              if (_rc == false) {                 _error = Marshal.GetLastWin32Error();                 Marshal.FreeHGlobal(_sid);                 throw (new Exception(new Win32Exception(_error).Message));             } else {                 Marshal.FreeHGlobal(_sid);                 return _sidString;             }         }     } }