HOWTO: Retrieve Account Name from SID in Textual Form

• Microsoft Win32 Application Programming Interface (API), on platform(s):
  • Microsoft Windows NT 4.0

SUMMARY

Some applications need to obtain the domain or user name of a user from a textual representation of a security identifier (SID). The Win32 API LookupAccountSid() can retrieve this information, but it requires a binary representation of the user's SID. This article demonstrates how to construct a binary representation of a SID from its textual form.

MORE INFORMATION

The GetBinarySid() function below analyzes the textual SID based on the same algorithm used in the following Knowledge Base article:

Q131320 How to Convert a Binary SID to Textual Form

Sample Code

#include <tchar.h>
#include <windows.h>
#include <stdio.h>

/*
    GetBinarySid() accepts a buffer that contains the textual
    representation of a SID. This function returns NULL
    if it fails. If the SID can be constructed successfully,
    a valid binary SID is returned. 

    This function requires TCHAR.H and the C runtime library.

    The following are macros defined in TCHAR.H that allow this
    function to be compiled with or without UNICODE defined. To
    replace these macros with direct calls to their corresponding
    ANSI functions first make sure this module is not compiled
    with UNICODE (or _UNICODE) defined.

      TCHAR           ANSI
     _stscanf() ->   sscanf()
     _tcschr()  ->   strchr()

*/ 

PSID GetBinarySid(
    LPTSTR TextualSid  // Buffer for Textual representation of SID.
    )
{
    PSID  pSid = 0;
    SID_IDENTIFIER_AUTHORITY identAuthority;
    TCHAR buffer[1024];
    int   i;

    LPTSTR ptr, ptr1;


    BYTE  nByteAuthorityCount = 0;
    DWORD dwSubAuthority[8] = {0, 0, 0, 0, 0, 0, 0, 0};

    ZeroMemory(&identAuthority, sizeof(identAuthority));

    lstrcpy(buffer, TextualSid);

    // S-SID_REVISION- + identifierauthority- + subauthorities- + NULL

    // Skip S
    if (!(ptr = _tcschr(buffer, _T('-'))))
    {
        return pSid;
    }

    // Skip -
    ptr++;

    // Skip SID_REVISION
    if (!(ptr = _tcschr(ptr, _T('-'))))
    {
        return pSid;
    }

    // Skip -
    ptr++;

    // Skip identifierauthority
    if (!(ptr1 = _tcschr(ptr, _T('-'))))
    {
        return pSid;
    }
    *ptr1= 0;

    if ((*ptr == '0') && (*(ptr+1) == 'x'))
    {
        _stscanf(ptr, _T("0x%02hx%02hx%02hx%02hx%02hx%02hx"),
            &identAuthority.Value[0],
            &identAuthority.Value[1],
            &identAuthority.Value[2],
            &identAuthority.Value[3],
            &identAuthority.Value[4],
            &identAuthority.Value[5]);
    }
    else
    {
        DWORD value;

        _stscanf(ptr, _T("%lu"), &value);

        identAuthority.Value[5] = (BYTE)(value & 0x000000FF);
        identAuthority.Value[4] = (BYTE)(value & 0x0000FF00) >> 8;
        identAuthority.Value[3] = (BYTE)(value & 0x00FF0000) >> 16;
        identAuthority.Value[2] = (BYTE)(value & 0xFF000000) >> 24;
    }

    // Skip -
    *ptr1 = '-';
    ptr = ptr1;
    ptr1++;

    for (i = 0; i < 8; i++)
    {
        // get subauthority
        if (!(ptr = _tcschr(ptr, '-')))
        {
            break;
        }
        *ptr=0;
        ptr++;
        nByteAuthorityCount++;
    }

    for (i = 0; i < nByteAuthorityCount; i++)
    {
        // Get subauthority.
        _stscanf(ptr1, _T("%lu"), &dwSubAuthority[i]);
        ptr1 += lstrlen(ptr1) + 1;
    }

    if (!AllocateAndInitializeSid(&identAuthority,
        nByteAuthorityCount,
        dwSubAuthority[0],
        dwSubAuthority[1],
        dwSubAuthority[2],
        dwSubAuthority[3],
        dwSubAuthority[4],
        dwSubAuthority[5],
        dwSubAuthority[6],
        dwSubAuthority[7],
        &pSid))
    {
        pSid = 0;
    }

    return pSid;
} 

Additional query words:

Keywords          : kbAccCtrl kbKernBase kbSecurity 
Version           : winnt:4.0
Platform          : winnt 
Issue type        : kbhowto 

Last Reviewed: March 10, 1999