Here are two small functions that enables you to convert a binary objectSID from Microsoft AD into a more usefull text version (formatted (S-1-5.....)).

// Converts a little-endian hex-number to one, that 'hexdec' can convert
function littleEndian($hex) {
    for ($x=strlen($hex)-2; $x >= 0; $x=$x-2) {
        $result .= substr($hex,$x,2);
    }
    return $result;
}

// Returns the textual SID
function binSIDtoText($binsid) {
    $hex_sid=bin2hex($binsid);
    $rev = hexdec(substr($hex_sid,0,2));          // Get revision-part of SID
    $subcount = hexdec(substr($hex_sid,2,2));    // Get count of sub-auth entries
    $auth = hexdec(substr($hex_sid,4,12));      // SECURITY_NT_AUTHORITY
    $result = "$rev-$auth";
    for ($x=0;$x < $subcount; $x++) {
        $subauth[$x] = hexdec(littleEndian(substr($hex_sid,16+($x*8),8)));  // get all SECURITY_NT_AUTHORITY
        $result .= "-".$subauth[$x];
    }
    return $result;
}

echo binSIDtoText($bin_sid);