diff --git a/core.php b/core.php
index 807ae72..6eccbe5 100644
--- a/core.php
+++ b/core.php
@@ -1,138 +1,175 @@
 <?php
 
 namespace Keruald;
 
 /**
  * Keruald, core libraries for Pluton and Xen engines.
  * 
  * Global functions
  */
 
 ///
 /// Strings
 ///
 
 /**
  * Pads a multibytes string to a certain length with another string
  *
  * @param string $str the input string
  * @param int $pad_length the target string size
  * @param string $pad_string the padding characters (optional, default is space)
  * @param int $pad_type STR_PAD_RIGHT, STR_PAD_LEFT, or STR_PAD_BOTH (optional, default is STR_PAD_RIGHT)
  * @param string the character encoding (optional)
  *
  * @return string the padded string
  *
  */
 function mb_str_pad($input, $pad_length, $pad_string = ' ', $pad_type = STR_PAD_RIGHT, $encoding = null) {
     // Inspired by Ronald Ulysses Swanson method
     // http://stackoverflow.com/a/27194169/1930997
     // who followed the str_pad PHP implementation.
 
     if ($encoding === null) {
         $encoding = mb_internal_encoding();
     }
 
     $padBefore = $pad_type === STR_PAD_BOTH || $pad_type === STR_PAD_LEFT;
     $padAfter = $pad_type === STR_PAD_BOTH || $pad_type === STR_PAD_RIGHT;
 
     $pad_length -= mb_strlen($input, $encoding);
     if ($padBefore && $padAfter) {
         $targetLength = $pad_length / 2;
     } else {
         $targetLength = $pad_length;
     }
     $strToRepeatLength = mb_strlen($pad_string, $encoding);
     $repeatTimes = ceil($targetLength / $strToRepeatLength);
     $repeatedString = str_repeat($pad_string, max(0, $repeatTimes)); // safe if used with valid Unicode sequences (any charset)
 
     $paddedString = '';
     if ($padBefore) {
         $paddedString = mb_substr($repeatedString, 0, floor($targetLength), $encoding);
     }
     $paddedString .= $input;
     if ($padAfter) {
         $paddedString .= mb_substr($repeatedString, 0, ceil($targetLength), $encoding);
     }
 
     return $paddedString;
 }
 
+///
+/// Identifiers
+///
+
+/**
+ * Generates a RFC 4211 compliant v4 UUID (random-based)
+ *
+ * @return string The UUID
+ */
+function uuid () {
+    //Code by Andrew Moore
+    //See http://php.net/manual/en/function.uniqid.php#94959
+    //    https://www.ietf.org/rfc/rfc4122.txt
+
+    return sprintf(
+        '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
+
+        // 32 bits for "time_low"
+        mt_rand(0, 0xffff), mt_rand(0, 0xffff),
+
+        // 16 bits for "time_mid"
+        mt_rand(0, 0xffff),
+
+        // 16 bits for "time_hi_and_version",
+        // four most significant bits holds version number 4
+        mt_rand(0, 0x0fff) | 0x4000,
+
+        // 16 bits, 8 bits for "clk_seq_hi_res",
+        // 8 bits for "clk_seq_low",
+        // two most significant bits holds zero and one for variant DCE1.1
+        mt_rand(0, 0x3fff) | 0x8000,
+
+        // 48 bits for "node"
+        mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
+    );
+}
+
 ///
 /// Error and debug
 ///
  
 /**
  * Prints human-readable information about a variable, wrapped in a <pre> block
  * 
  * @param mixed $variable the variable to dump
  */
 function dprint_r ($variable) {
     echo '<pre>';
     print_r($variable);
     echo '</pre>';
 }
 
 /**
  * Prints human-readable information about a variable, wrapped in a <pre> block
  * then dies
  * 
  * @param mixed $variable the variable to dump
  */
 function dieprint_r ($variable) {
     dprint_r($variable);
     die;
 };
 
 ///
 /// Client information
 ///
 
 /**
  * Returns the full header or the IP part of it
  *
  * @param string $value The header value
  * @return string the IP part
  */
 function extract_client_ip_from_header ($value) {
     if (strpos($value, ',') !== false) {
         //Header contains 'clientIP, proxyIP, anotherProxyIP'
         //The first value is so the one to return.
         //See draft-ietf-appsawg-http-forwarded-10.
         $ips = explode(',', $value, 2);
         return trim($ips[0]);
     }
 
     return $value;
 }
 
 /**
  * Gets remote IP address.
  *
  * This is intended as a drop-in replacement for $_SERVER['REMOTE_ADDR'],
  * which takes in consideration proxy values.
  */
 function get_remote_addr () {
     $candidates = [
         //Standard header provided by draft-ietf-appsawg-http-forwarded-10
         'HTTP_X_FORWARDED_FOR',
 
         //Legacy headers
         'HTTP_CLIENT_IP',
         'HTTP_FORWARDED',
         'HTTP_FORWARDED_FOR',
         'HTTP_X_CLUSTER_CLIENT_IP',
         'HTTP_X_FORWARDED',
 
         //Default header if no proxy information could be detected
         'REMOTE_ADDR',
     ];
 
     foreach ($candidates as $candidate) {
         if (array_key_exists($candidate, $_SERVER)) {
             return extract_client_ip_from_header($_SERVER[$candidate]);
         }
     }
 
     return '';
 }
diff --git a/tests/CoreTest.php b/tests/CoreTest.php
index dcef8b6..47e9fe0 100644
--- a/tests/CoreTest.php
+++ b/tests/CoreTest.php
@@ -1,81 +1,98 @@
 <?php
 
 namespace Keruald;
 
 class CoreTest extends \PHPUnit_Framework_Testcase {
 
     ///
     /// Strings
     ///
 
     function test_mb_str_pad () {
         // Tests from http://3v4l.org/UnXTF
         // http://web.archive.org/web/20150711100913/http://3v4l.org/UnXTF
 
         $this->assertEquals('àèòàFOOàèòà', mb_str_pad("FOO", 11, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('àèòFOOàèòà', mb_str_pad("FOO", 10, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('àèòBAAZàèòà', mb_str_pad("BAAZ", 11, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('àèòBAAZàèò', mb_str_pad("BAAZ", 10, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 6, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 1, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 0, "àèò", STR_PAD_BOTH, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", -10, "àèò", STR_PAD_BOTH, "UTF-8"));
 
         $this->assertEquals('àèòàèòàèFOO', mb_str_pad("FOO", 11, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('àèòàèòàFOO', mb_str_pad("FOO", 10, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('àèòàèòàBAAZ', mb_str_pad("BAAZ", 11, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('àèòàèòBAAZ', mb_str_pad("BAAZ", 10, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 6, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 1, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 0, "àèò", STR_PAD_LEFT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", -10, "àèò", STR_PAD_LEFT, "UTF-8"));
 
         $this->assertEquals('FOOàèòàèòàè', mb_str_pad("FOO", 11, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('FOOàèòàèòà', mb_str_pad("FOO", 10, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('BAAZàèòàèòà', mb_str_pad("BAAZ", 11, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('BAAZàèòàèò', mb_str_pad("BAAZ", 10, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 6, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 1, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", 0, "àèò", STR_PAD_RIGHT, "UTF-8"));
         $this->assertEquals('FOOBAR', mb_str_pad("FOOBAR", -10, "àèò", STR_PAD_RIGHT, "UTF-8"));
     }
 
+    ///
+    /// Identifiers
+    ///
+
+    function test_uuid () {
+        $uuid = uuid();
+        $this->assertEquals(36, strlen($uuid));
+        for ($i = 0 ; $i < 36 ; $i++) {
+            if ($i == 8 | $i == 13 || $i == 18 || $i == 23) {
+                $this->assertEquals("-", $uuid[$i], "Dash were expected.");
+                continue;
+            }
+
+            $this->assertRegExp('/[0-9a-f]/', $uuid[$i], "Lowercase hexadecimal digit were expected.");
+        }
+    }
+
     ///
     /// Client information
     ///
 
     function test_extract_client_ip_from_header () {
         $values = [
             //Each value should return 10.0.0.3
             '10.0.0.3',
             '10.0.0.3,10.0.0.4',
             '10.0.0.3, 10.0.0.4',
             '10.0.0.3, 10.0.0.4, lorem ipsum dolor',
         ];
         foreach ($values as $value) {
             $this->assertEquals(
                 '10.0.0.3',
                 extract_client_ip_from_header($value)
             );
         }
 
         $this->assertEmpty(
             extract_client_ip_from_header('')
         );
     }
 
     function test_get_remote_addr () {
         $this->assertEmpty(get_remote_addr());
 
         $_SERVER = [
             'REMOTE_ADDR' => '10.0.0.2'
         ];
         $this->assertEquals('10.0.0.2', get_remote_addr());
 
         $_SERVER += [
             'HTTP_X_FORWARDED_FOR' => '10.0.0.3',
             'HTTP_CLIENT_IP' => '10.0.0.4',
         ];
         $this->assertEquals('10.0.0.3', get_remote_addr(), "HTTP_X_FORWARDED_FOR must be prioritized.");
     }
 }