User recognition without cookies or local storage

Question

I'm building an analytic tool and I can currently get the user's IP address, browser and operating system from their user agent.

I'm wondering if there is a possibility to detect the same user without using cookies or local storage? I'm not expecting code examples here; just a simple hint of where to look further.

Forgot to mention that it would need to be cross-browser compatible if it's the same computer/device. Basically I'm after device recognition not really the user.

Answer 1

Introduction

If I understand you correctly, you need to identify a user for whom you don't have a Unique Identifier, so you want to figure out who they are by matching Random Data. You can't store the user's identity reliably because:

• Cookies Can be deleted
• IP address Can change
• Browser Can Change
• Browser Cache may be deleted

A Java Applet or Com Object would have been an easy solution using a hash of hardware information, but these days people are so security-aware that it would be difficult to get people to install these kinds of programs on their system. This leaves you stuck with using Cookies and other, similar tools.

Cookies and other, similar tools

You might consider building a Data Profile, then using Probability tests to identify a Probable User. A profile useful for this can be generated by some combination of the following:

1. IP Address
   • Real IP Address
   • Proxy IP Address (users often use the same proxy repeatedly)
2. Cookies
   • HTTP Cookies
   • Session Cookies
   • 3rd Party Cookies
   • Flash Cookies (most people don't know how to delete these)
3. Web Bugs (less reliable because bugs get fixed, but still useful)
   • PDF Bug
   • Flash Bug
   • Java Bug
4. Browsers
   • Click Tracking (many users visit the same series of pages on each visit)
   • Browsers Finger Print   - Installed Plugins (people often have varied, somewhat unique sets of plugins)
   • Cached Images (people sometimes delete their cookies but leave cached images)
   • Using Blobs
   • URL(s) (browser history or cookies may contain unique user id's in URLs, such as https://stackoverflow.com/users/1226894 or http://www.facebook.com/barackobama?fref=ts)
   • System Fonts Detection (this is a little-known but often unique key signature)
5. HTML5 & Javascript
   • HTML5 LocalStorage
   • HTML5 Geolocation API and Reverse Geocoding
   • Architecture, OS Language, System Time, Screen Resolution, etc.
   • Network Information API
   • Battery Status API

The items I listed are, of course, just a few possible ways a user can be identified uniquely. There are many more.

With this set of Random Data elements to build a Data Profile from, what's next?

The next step is to develop some Fuzzy Logic, or, better yet, an Artificial Neural Network (which uses fuzzy logic). In either case, the idea is to train your system, and then combine its training with Bayesian Inference to increase the accuracy of your results.

The NeuralMesh library for PHP allows you to generate Artificial Neural Networks. To implement Bayesian Inference, check out the following links:

• Implement Bayesian inference using PHP, Part 1
• Implement Bayesian inference using PHP, Part 2
• Implement Bayesian inference using PHP, Part 3

At this point, you may be thinking:

Why so much Math and Logic for a seemingly simple task?

Basically, because it is not a simple task. What you are trying to achieve is, in fact, Pure Probability. For example, given the following known users:

User1 = A + B + C + D + G + K
User2 = C + D + I + J + K + F

When you receive the following data:

B + C + E + G + F + K

The question which you are essentially asking is:

What is the probability that the received data (B + C + E + G + F + K) is actually User1 or User2? And which of those two matches is most probable?

In order to effectively answer this question, you need to understand Frequency vs Probability Format and why Joint Probability might be a better approach. The details are too much to get into here (which is why I'm giving you links), but a good example would be a Medical Diagnosis Wizard Application, which uses a combination of symptoms to identify possible diseases.

Think for a moment of the series of data points which comprise your Data Profile (B + C + E + G + F + K in the example above) as Symptoms, and Unknown Users as Diseases. By identifying the disease, you can further identify an appropriate treatment (treat this user as User1).

Obviously, a Disease for which we have identified more than 1 Symptom is easier to identify. In fact, the more Symptoms we can identify, the easier and more accurate our diagnosis is almost certain to be.

Are there any other alternatives?

Of course. As an alternative measure, you might create your own simple scoring algorithm, and base it on exact matches. This is not as efficient as probability, but may be simpler for you to implement.

As an example, consider this simple score chart:

+-------------------------+--------+------------+
|        Property         | Weight | Importance |
+-------------------------+--------+------------+
| Real IP address         |     60 |          5 |
| Used proxy IP address   |     40 |          4 |
| HTTP Cookies            |     80 |          8 |
| Session Cookies         |     80 |          6 |
| 3rd Party Cookies       |     60 |          4 |
| Flash Cookies           |     90 |          7 |
| PDF Bug                 |     20 |          1 |
| Flash Bug               |     20 |          1 |
| Java Bug                |     20 |          1 |
| Frequent Pages          |     40 |          1 |
| Browsers Finger Print   |     35 |          2 |
| Installed Plugins       |     25 |          1 |
| Cached Images           |     40 |          3 |
| URL                     |     60 |          4 |
| System Fonts Detection  |     70 |          4 |
| Localstorage            |     90 |          8 |
| Geolocation             |     70 |          6 |
| AOLTR                   |     70 |          4 |
| Network Information API |     40 |          3 |
| Battery Status API      |     20 |          1 |
+-------------------------+--------+------------+

For each piece of information which you can gather on a given request, award the associated score, then use Importance to resolve conflicts when scores are the same.

Proof of Concept

For a simple proof of concept, please take a look at Perceptron. Perceptron is a RNA Model that is generally used in pattern recognition applications. There is even an old PHP Class which implements it perfectly, but you would likely need to modify it for your purposes.

Despite being a great tool, Perceptron can still return multiple results (possible matches), so using a Score and Difference comparison is still useful to identify the best of those matches.

Assumptions

• Store all possible information about each user (IP, cookies, etc.)
• Where result is an exact match, increase score by 1
• Where result is not an exact match, decrease score by 1

Expectation

1. Generate RNA labels
2. Generate random users emulating a database
3. Generate a single Unknown user
4. Generate Unknown user RNA and Values
5. The system will merge RNA information and teach the Perceptron
6. After training the Perceptron, the system will have a set of weightings
7. You can now test the Unknown user's pattern and the Perceptron will produce a result set.
8. Store all Positive matches
9. Sort the matches first by Score, then by Difference (as described above)
10. Output the two closest matches, or, if no matches are found, output empty results

Code for Proof of Concept

$features = array(
    'Real IP address' => .5,
    'Used proxy IP address' => .4,
    'HTTP Cookies' => .9,
    'Session Cookies' => .6,
    '3rd Party Cookies' => .6,
    'Flash Cookies' => .7,
    'PDF Bug' => .2,
    'Flash Bug' => .2,
    'Java Bug' => .2,
    'Frequent Pages' => .3,
    'Browsers Finger Print' => .3,
    'Installed Plugins' => .2,
    'URL' => .5,
    'Cached PNG' => .4,
    'System Fonts Detection' => .6,
    'Localstorage' => .8,
    'Geolocation' => .6,
    'AOLTR' => .4,
    'Network Information API' => .3,
    'Battery Status API' => .2
);

// Get RNA Lables
$labels = array();
$n = 1;
foreach ($features as $k => $v) {
    $labels[$k] = "x" . $n;
    $n ++;
}

// Create Users
$users = array();
for($i = 0, $name = "A"; $i < 5; $i ++, $name ++) {
    $users[] = new Profile($name, $features);
}

// Generate Unknown User
$unknown = new Profile("Unknown", $features);

// Generate Unknown RNA
$unknownRNA = array(
    0 => array("o" => 1),
    1 => array("o" => - 1)
);

// Create RNA Values
foreach ($unknown->data as $item => $point) {
    $unknownRNA[0][$labels[$item]] = $point;
    $unknownRNA[1][$labels[$item]] = (- 1 * $point);
}

// Start Perception Class
$perceptron = new Perceptron();

// Train Results
$trainResult = $perceptron->train($unknownRNA, 1, 1);

// Find matches
foreach ($users as $name => &$profile) {
    // Use shorter labels
    $data = array_combine($labels, $profile->data);
    if ($perceptron->testCase($data, $trainResult) == true) {
        $score = $diff = 0;

        // Determing the score and diffrennce
        foreach ($unknown->data as $item => $found) {
            if ($unknown->data[$item] === $profile->data[$item]) {
                if ($profile->data[$item] > 0) {
                    $score += $features[$item];
                } else {
                    $diff += $features[$item];
                }
            }
        }
        // Ser score and diff
        $profile->setScore($score, $diff);
        $matchs[] = $profile;
    }
}

// Sort bases on score and Output
if (count($matchs) > 1) {
    usort($matchs, function ($a, $b) {
        // If score is the same use diffrence
        if ($a->score == $b->score) {
            // Lower the diffrence the better
            return $a->diff == $b->diff ? 0 : ($a->diff > $b->diff ? 1 : - 1);
        }
        // The higher the score the better
        return $a->score > $b->score ? - 1 : 1;
    });

    echo "<br />Possible Match ", implode(",", array_slice(array_map(function ($v) {
        return sprintf(" %s (%0.4f|%0.4f) ", $v->name, $v->score,$v->diff);
    }, $matchs), 0, 2));
} else {
    echo "<br />No match Found ";
}

Output:

Possible Match D (0.7416|0.16853),C (0.5393|0.2809)

Print_r of "D":

echo "<pre>";
print_r($matchs[0]);


Profile Object(
    [name] => D
    [data] => Array (
        [Real IP address] => -1
        [Used proxy IP address] => -1
        [HTTP Cookies] => 1
        [Session Cookies] => 1
        [3rd Party Cookies] => 1
        [Flash Cookies] => 1
        [PDF Bug] => 1
        [Flash Bug] => 1
        [Java Bug] => -1
        [Frequent Pages] => 1
        [Browsers Finger Print] => -1
        [Installed Plugins] => 1
        [URL] => -1
        [Cached PNG] => 1
        [System Fonts Detection] => 1
        [Localstorage] => -1
        [Geolocation] => -1
        [AOLTR] => 1
        [Network Information API] => -1
        [Battery Status API] => -1
    )
    [score] => 0.74157303370787
    [diff] => 0.1685393258427
    [base] => 8.9
)

If Debug = true you would be able to see Input (Sensor & Desired), Initial Weights, Output (Sensor, Sum, Network), Error, Correction and Final Weights.

+----+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----+----+---------+---------+---------+---------+---------+---------+---------+---------+---------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----------+
| o  | x1 | x2 | x3 | x4 | x5 | x6 | x7 | x8 | x9 | x10 | x11 | x12 | x13 | x14 | x15 | x16 | x17 | x18 | x19 | x20 | Bias | Yin | Y  | deltaW1 | deltaW2 | deltaW3 | deltaW4 | deltaW5 | deltaW6 | deltaW7 | deltaW8 | deltaW9 | deltaW10 | deltaW11 | deltaW12 | deltaW13 | deltaW14 | deltaW15 | deltaW16 | deltaW17 | deltaW18 | deltaW19 | deltaW20 | W1 | W2 | W3 | W4 | W5 | W6 | W7 | W8 | W9 | W10 | W11 | W12 | W13 | W14 | W15 | W16 | W17 | W18 | W19 | W20 | deltaBias |
+----+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----+----+---------+---------+---------+---------+---------+---------+---------+---------+---------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----------+
| 1  | 1  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1    | 0   | -1 | 0       | -1      | -1      | -1      | -1      | -1      | -1      | 1       | 1       | 1        | 1        | 1        | 1        | 1        | -1       | -1       | -1       | -1       | 1        | 1        | 0  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1         |
| -1 | -1 | 1  | 1  | 1  | 1  | 1  | 1  | -1 | -1 | -1  | -1  | -1  | -1  | -1  | 1   | 1   | 1   | 1   | -1  | -1  | 1    | -19 | -1 | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1         |
| -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --   | --  | -- | --      | --      | --      | --      | --      | --      | --      | --      | --      | --       | --       | --       | --       | --       | --       | --       | --       | --       | --       | --       | -- | -- | -- | -- | -- | -- | -- | -- | -- | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --        |
| 1  | 1  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1    | 19  | 1  | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1         |
| -1 | -1 | 1  | 1  | 1  | 1  | 1  | 1  | -1 | -1 | -1  | -1  | -1  | -1  | -1  | 1   | 1   | 1   | 1   | -1  | -1  | 1    | -19 | -1 | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0       | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0        | 0  | -1 | -1 | -1 | -1 | -1 | -1 | 1  | 1  | 1   | 1   | 1   | 1   | 1   | -1  | -1  | -1  | -1  | 1   | 1   | 1         |
| -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --   | --  | -- | --      | --      | --      | --      | --      | --      | --      | --      | --      | --       | --       | --       | --       | --       | --       | --       | --       | --       | --       | --       | -- | -- | -- | -- | -- | -- | -- | -- | -- | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --  | --        |
+----+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+------+-----+----+---------+---------+---------+---------+---------+---------+---------+---------+---------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----------+----+----+----+----+----+----+----+----+----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----------+

x1 to x20 represent the features converted by the code.

// Get RNA Labels
$labels = array();
$n = 1;
foreach ( $features as $k => $v ) {
    $labels[$k] = "x" . $n;
    $n ++;
}

Here is an online demo

Class Used:

class Profile {
    public $name, $data = array(), $score, $diff, $base;

    function __construct($name, array $importance) {
        $values = array(-1, 1); // Perception values
        $this->name = $name;
        foreach ($importance as $item => $point) {
            // Generate Random true/false for real Items
            $this->data[$item] = $values[mt_rand(0, 1)];
        }
        $this->base = array_sum($importance);
    }

    public function setScore($score, $diff) {
        $this->score = $score / $this->base;
        $this->diff = $diff / $this->base;
    }
}

Modified Perceptron Class

class Perceptron {
    private $w = array();
    private $dw = array();
    public $debug = false;

    private function initialize($colums) {
        // Initialize perceptron vars
        for($i = 1; $i <= $colums; $i ++) {
            // weighting vars
            $this->w[$i] = 0;
            $this->dw[$i] = 0;
        }
    }

    function train($input, $alpha, $teta) {
        $colums = count($input[0]) - 1;
        $weightCache = array_fill(1, $colums, 0);
        $checkpoints = array();
        $keepTrainning = true;

        // Initialize RNA vars
        $this->initialize(count($input[0]) - 1);
        $just_started = true;
        $totalRun = 0;
        $yin = 0;

        // Trains RNA until it gets stable
        while ($keepTrainning == true) {
            // Sweeps each row of the input subject
            foreach ($input as $row_counter => $row_data) {
                // Finds out the number of columns the input has
                $n_columns = count($row_data) - 1;

                // Calculates Yin
                $yin = 0;
                for($i = 1; $i <= $n_columns; $i ++) {
                    $yin += $row_data["x" . $i] * $weightCache[$i];
                }

                // Calculates Real Output
                $Y = ($yin <= 1) ? - 1 : 1;

                // Sweeps columns ...
                $checkpoints[$row_counter] = 0;
                for($i = 1; $i <= $n_columns; $i ++) {
                    /** DELTAS **/
                    // Is it the first row?
                    if ($just_started == true) {
                        $this->dw[$i] = $weightCache[$i];
                        $just_started = false;
                        // Found desired output?
                    } elseif ($Y == $row_data["o"]) {
                        $this->dw[$i] = 0;
                        // Calculates Delta Ws
                    } else {
                        $this->dw[$i] = $row_data["x" . $i] * $row_data["o"];
                    }

                    /** WEIGHTS **/
                    // Calculate Weights
                    $this->w[$i] = $this->dw[$i] + $weightCache[$i];
                    $weightCache[$i] = $this->w[$i];

                    /** CHECK-POINT **/
                    $checkpoints[$row_counter] += $this->w[$i];
                } // END - for

                foreach ($this->w as $index => $w_item) {
                    $debug_w["W" . $index] = $w_item;
                    $debug_dw["deltaW" . $index] = $this->dw[$index];
                }

                // Special for script debugging
                $debug_vars[] = array_merge($row_data, array(
                    "Bias" => 1,
                    "Yin" => $yin,
                    "Y" => $Y
                ), $debug_dw, $debug_w, array(
                    "deltaBias" => 1
                ));
            } // END - foreach

            // Special for script debugging
             $empty_data_row = array();
            for($i = 1; $i <= $n_columns; $i ++) {
                $empty_data_row["x" . $i] = "--";
                $empty_data_row["W" . $i] = "--";
                $empty_data_row["deltaW" . $i] = "--";
            }
            $debug_vars[] = array_merge($empty_data_row, array(
                "o" => "--",
                "Bias" => "--",
                "Yin" => "--",
                "Y" => "--",
                "deltaBias" => "--"
            ));

            // Counts training times
            $totalRun ++;

            // Now checks if the RNA is stable already
            $referer_value = end($checkpoints);
            // if all rows match the desired output ...
            $sum = array_sum($checkpoints);
            $n_rows = count($checkpoints);
            if ($totalRun > 1 && ($sum / $n_rows) == $referer_value) {
                $keepTrainning = false;
            }
        } // END - while

        // Prepares the final result
        $result = array();
        for($i = 1; $i <= $n_columns; $i ++) {
            $result["w" . $i] = $this->w[$i];
        }

        $this->debug($this->print_html_table($debug_vars));

        return $result;
    } // END - train
    function testCase($input, $results) {
        // Sweeps input columns
        $result = 0;
        $i = 1;
        foreach ($input as $column_value) {
            // Calculates teste Y
            $result += $results["w" . $i] * $column_value;
            $i ++;
        }
        // Checks in each class the test fits
        return ($result > 0) ? true : false;
    } // END - test_class

    // Returns the html code of a html table base on a hash array
    function print_html_table($array) {
        $html = "";
        $inner_html = "";
        $table_header_composed = false;
        $table_header = array();

        // Builds table contents
        foreach ($array as $array_item) {
            $inner_html .= "<tr>\n";
            foreach ( $array_item as $array_col_label => $array_col ) {
                $inner_html .= "<td>\n";
                $inner_html .= $array_col;
                $inner_html .= "</td>\n";

                if ($table_header_composed == false) {
                    $table_header[] = $array_col_label;
                }
            }
            $table_header_composed = true;
            $inner_html .= "</tr>\n";
        }

        // Builds full table
        $html = "<table border=1>\n";
        $html .= "<tr>\n";
        foreach ($table_header as $table_header_item) {
            $html .= "<td>\n";
            $html .= "<b>" . $table_header_item . "</b>";
            $html .= "</td>\n";
        }
        $html .= "</tr>\n";

        $html .= $inner_html . "</table>";

        return $html;
    } // END - print_html_table

    // Debug function
    function debug($message) {
        if ($this->debug == true) {
            echo "<b>DEBUG:</b> $message";
        }
    } // END - debug
} // END - class

Conclusion

Identifying a user without a Unique Identifier is not a straight-forward or simple task. it is dependent upon gathering a sufficient amount of Random Data which you are able to gather from the user by a variety of methods.

Even if you choose not to use an Artificial Neural Network, I suggest at least using a Simple Probability Matrix with priorities and likelihoods - and I hope the code and examples provided above give you enough to go on.

Answer 2

This technique (to detect same users without cookies - or even without ip address) is called browser fingerprinting. Basically you crawl as information about the browser as you can - better results can be achieved with javascript, flash or java (f.ex. installed extensions, fonts, etc.). After that, you can store the results hashed, if you want.

It's not infallible, but:

83.6% of the browsers seen had a unique fingerprint; among those with Flash or Java enabled, 94.2%. This does not include cookies!

More info:

• https://panopticlick.eff.org/
• https://wiki.mozilla.org/Fingerprinting
• https://www.browserleaks.com/

Answer 3

The above mentioned thumbprinting works, but can still suffer colisions.

One way is to add UID to the url of each interaction with the user.

http://someplace.com/12899823/user/profile

Where every link in the site is adapted with this modifier. It is similar to the way ASP.Net used to work using FORM data between pages.