diff --git a/.gitignore b/.gitignore
index 5982f9b..eb45390 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,8 @@
 !application/logs/index.html
 !application/logs/.htaccess
 
+composer.lock
+
 user_guide_src/build/*
 user_guide_src/cilexer/build/*
 user_guide_src/cilexer/dist/*
diff --git a/.travis.yml b/.travis.yml
index 6b90a5f..2a0be4d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,11 +26,10 @@
   - sh -c "if [ '$DB' = 'pgsql' ] || [ '$DB' = 'pdo/pgsql' ]; then psql -c 'create database ci_test;' -U postgres; fi"
   - sh -c "if [ '$DB' = 'mysql' ] || [ '$DB' = 'mysqli' ] || [ '$DB' = 'pdo/mysql' ]; then mysql -e 'create database IF NOT EXISTS ci_test;'; fi"
 
-script: phpunit -d zend.enable_gc=0 -d date.timezone=UTC --coverage-text --configuration tests/travis/$DB.phpunit.xml
+script: phpunit -d zend.enable_gc=0 -d date.timezone=UTF -d mbstring.func_overload=7 -d mbstring.internal_encoding=UTF-8 vendor/bin/phpunit --coverage-text --configuration tests/travis/$DB.phpunit.xml
 
 matrix:
   allow_failures:
-    - php: 5.3
     - php: hhvm
   exclude:
     - php: hhvm
diff --git a/composer.json b/composer.json
index 64d1be1..0a898d2 100644
--- a/composer.json
+++ b/composer.json
@@ -17,6 +17,7 @@
 		"paragonie/random_compat": "Provides better randomness in PHP 5.x"
 	},
 	"require-dev": {
-		"mikey179/vfsStream": "1.1.*"
+		"mikey179/vfsStream": "1.1.*",
+		"phpunit/phpunit": "4.* || 5.*"
 	}
-}
\ No newline at end of file
+}
diff --git a/system/helpers/text_helper.php b/system/helpers/text_helper.php
index 07c01c3..217729b 100644
--- a/system/helpers/text_helper.php
+++ b/system/helpers/text_helper.php
@@ -138,7 +138,10 @@
 	function ascii_to_entities($str)
 	{
 		$out = '';
-		for ($i = 0, $s = strlen($str) - 1, $count = 1, $temp = array(); $i <= $s; $i++)
+		$length = defined('MB_OVERLOAD_STRING')
+			? mb_strlen($str, '8bit') - 1
+			: strlen($str) - 1;
+		for ($i = 0, $count = 1, $temp = array(); $i <= $length; $i++)
 		{
 			$ordinal = ord($str[$i]);
 
@@ -176,7 +179,7 @@
 					$temp = array();
 				}
 				// If this is the last iteration, just output whatever we have
-				elseif ($i === $s)
+				elseif ($i === $length)
 				{
 					$out .= '&#'.implode(';', $temp).';';
 				}
diff --git a/system/libraries/Encrypt.php b/system/libraries/Encrypt.php
index 46f3747..ebcc6e8 100644
--- a/system/libraries/Encrypt.php
+++ b/system/libraries/Encrypt.php
@@ -122,7 +122,7 @@
 
 			$key = config_item('encryption_key');
 
-			if ( ! strlen($key))
+			if ( ! self::strlen($key))
 			{
 				show_error('In order to use the encryption class requires that you set an encryption key in your config file.');
 			}
@@ -252,7 +252,7 @@
 		$string = $this->_xor_merge($string, $key);
 
 		$dec = '';
-		for ($i = 0, $l = strlen($string); $i < $l; $i++)
+		for ($i = 0, $l = self::strlen($string); $i < $l; $i++)
 		{
 			$dec .= ($string[$i++] ^ $string[$i]);
 		}
@@ -275,7 +275,8 @@
 	{
 		$hash = $this->hash($key);
 		$str = '';
-		for ($i = 0, $ls = strlen($string), $lh = strlen($hash); $i < $ls; $i++)
+
+		for ($i = 0, $ls = self::strlen($string), $lh = self::strlen($hash); $i < $ls; $i++)
 		{
 			$str .= $string[$i] ^ $hash[($i % $lh)];
 		}
@@ -295,7 +296,7 @@
 	public function mcrypt_encode($data, $key)
 	{
 		$init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());
-		$init_vect = mcrypt_create_iv($init_size, MCRYPT_RAND);
+		$init_vect = mcrypt_create_iv($init_size, MCRYPT_DEV_URANDOM);
 		return $this->_add_cipher_noise($init_vect.mcrypt_encrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), $key);
 	}
 
@@ -313,13 +314,14 @@
 		$data = $this->_remove_cipher_noise($data, $key);
 		$init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());
 
-		if ($init_size > strlen($data))
+		if ($init_size > self::strlen($data))
 		{
 			return FALSE;
 		}
 
-		$init_vect = substr($data, 0, $init_size);
-		$data = substr($data, $init_size);
+		$init_vect = self::substr($data, 0, $init_size);
+		$data      = self::substr($data, $init_size);
+
 		return rtrim(mcrypt_decrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), "\0");
 	}
 
@@ -339,7 +341,7 @@
 		$key = $this->hash($key);
 		$str = '';
 
-		for ($i = 0, $j = 0, $ld = strlen($data), $lk = strlen($key); $i < $ld; ++$i, ++$j)
+		for ($i = 0, $j = 0, $ld = self::strlen($data), $lk = self::strlen($key); $i < $ld; ++$i, ++$j)
 		{
 			if ($j >= $lk)
 			{
@@ -369,7 +371,7 @@
 		$key = $this->hash($key);
 		$str = '';
 
-		for ($i = 0, $j = 0, $ld = strlen($data), $lk = strlen($key); $i < $ld; ++$i, ++$j)
+		for ($i = 0, $j = 0, $ld = self::strlen($data), $lk = self::strlen($key); $i < $ld; ++$i, ++$j)
 		{
 			if ($j >= $lk)
 			{
@@ -477,4 +479,43 @@
 		return hash($this->_hash_type, $str);
 	}
 
+	// --------------------------------------------------------------------
+
+	/**
+	 * Byte-safe strlen()
+	 *
+	 * @param	string	$str
+	 * @return	int
+	 */
+	protected static function strlen($str)
+	{
+		return defined('MB_OVERLOAD_STRING')
+			? mb_strlen($str, '8bit')
+			: strlen($str);
+	}
+
+	// --------------------------------------------------------------------
+
+	/**
+	 * Byte-safe substr()
+	 *
+	 * @param	string	$str
+	 * @param	int	$start
+	 * @param	int	$length
+	 * @return	string
+	 */
+	protected static function substr($str, $start, $length = NULL)
+	{
+		if (defined('MB_OVERLOAD_STRING'))
+		{
+			// mb_substr($str, $start, null, '8bit') returns an empty
+			// string on PHP 5.3
+			isset($length) OR $length = ($start >= 0 ? self::strlen($str) - $start : -$start);
+			return mb_substr($str, $start, $length, '8bit');
+		}
+
+		return isset($length)
+			? substr($str, $start, $length)
+			: substr($str, $start);
+	}
 }
diff --git a/system/libraries/Encryption.php b/system/libraries/Encryption.php
index 74832ed..c1e454d 100644
--- a/system/libraries/Encryption.php
+++ b/system/libraries/Encryption.php
@@ -135,11 +135,11 @@
 	);
 
 	/**
-	 * mbstring.func_override flag
+	 * mbstring.func_overload flag
 	 *
 	 * @var	bool
 	 */
-	protected static $func_override;
+	protected static $func_overload;
 
 	// --------------------------------------------------------------------
 
@@ -161,7 +161,7 @@
 			show_error('Encryption: Unable to find an available encryption driver.');
 		}
 
-		isset(self::$func_override) OR self::$func_override = (extension_loaded('mbstring') && ini_get('mbstring.func_override'));
+		isset(self::$func_overload) OR self::$func_overload = (extension_loaded('mbstring') && ini_get('mbstring.func_overload'));
 		$this->initialize($params);
 
 		if ( ! isset($this->_key) && self::strlen($key = config_item('encryption_key')) > 0)
@@ -911,7 +911,7 @@
 	 */
 	protected static function strlen($str)
 	{
-		return (self::$func_override)
+		return (self::$func_overload)
 			? mb_strlen($str, '8bit')
 			: strlen($str);
 	}
@@ -928,7 +928,7 @@
 	 */
 	protected static function substr($str, $start, $length = NULL)
 	{
-		if (self::$func_override)
+		if (self::$func_overload)
 		{
 			// mb_substr($str, $start, null, '8bit') returns an empty
 			// string on PHP 5.3
diff --git a/tests/codeigniter/libraries/Encryption_test.php b/tests/codeigniter/libraries/Encryption_test.php
index 96e52ad..99c5d4b 100644
--- a/tests/codeigniter/libraries/Encryption_test.php
+++ b/tests/codeigniter/libraries/Encryption_test.php
@@ -94,10 +94,22 @@
 		}
 
 		// Test default length, it must match the digest size
-		$this->assertEquals(64, strlen($this->encryption->hkdf('foobar', 'sha512')));
+		$hkdf_result = $this->encryption->hkdf('foobar', 'sha512');
+		$this->assertEquals(
+			64,
+			defined('MB_OVERLOAD_STRING')
+				? mb_strlen($hkdf_result, '8bit')
+				: strlen($hkdf_result)
+		);
 
 		// Test maximum length (RFC5869 says that it must be up to 255 times the digest size)
-		$this->assertEquals(12240, strlen($this->encryption->hkdf('foobar', 'sha384', NULL, 48 * 255)));
+		$hkdf_result = $this->encryption->hkdf('foobar', 'sha384', NULL, 48 * 255);
+		$this->assertEquals(
+			12240,
+			defined('MB_OVERLOAD_STRING')
+				? mb_strlen($hkdf_result, '8bit')
+				: strlen($hkdf_result)
+		);
 		$this->assertFalse($this->encryption->hkdf('foobar', 'sha224', NULL, 28 * 255 + 1));
 
 		// CI-specific test for an invalid digest
diff --git a/tests/phpunit.xml b/tests/phpunit.xml
index 96c3af9..875198c 100644
--- a/tests/phpunit.xml
+++ b/tests/phpunit.xml
@@ -17,10 +17,8 @@
 		</testsuite>
 	</testsuites>
 	<filter>
-		<blacklist>
-			<directory suffix=".php">PEAR_INSTALL_DIR</directory>
-			<directory suffix=".php">PHP_LIBDIR</directory>
-			<directory suffix=".php">../vendor</directory>
-		</blacklist>
+		<whitelist>
+			<directory suffix=".php">../system/</directory>
+		</whitelist>
 	</filter>
-</phpunit>
\ No newline at end of file
+</phpunit>
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 2769990..17069ca 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -7,6 +7,12 @@
 
 Release Date: Not Released
 
+-  **Security**
+
+   -  Updated :doc:`Encrypt Library <libraries/encrypt>` (DEPRECATED) to call ``mcrypt_create_iv()`` with ``MCRYPT_DEV_URANDOM``.
+   -  Fixed byte-safety issues in :doc:`Encrypt Library <libraries/encrypt>` (DEPRECATED) when ``mbstring.func_overload`` is enabled.
+   -  Fixed byte-safety issues in :doc:`Encryption Library <libraries/encryption>` when ``mbstring.func_overload`` is enabled.
+
 -  General Changes
 
    -  Updated the :doc:`Image Manipulation Library <libraries/image_lib>` to work-around an issue with some JPEGs when using GD.
@@ -18,6 +24,7 @@
 -  Fixed a bug (#4977) - :doc:`Loader Library <libraries/loader>` method ``helper()`` could accept any character as a filename extension separator.
 -  Fixed a regression where the :doc:`Session Library <libraries/sessions>` would fail on a ``session_regenerate_id(TRUE)`` call with the 'database' driver.
 -  Fixed a bug (#4987) - :doc:`Query Builder <database/query_builder>` caching didn't keep track of table aliases.
+-  Fixed a bug where :doc:`Text Helper <helpers/text_helper>` function ``ascii_to_entities()`` wasn't byte-safe when ``mbstring.func_overload`` is enabled.
 
 Version 3.1.3
 =============
@@ -82,7 +89,7 @@
 -  Fixed a regression (#4874) - :doc:`Session Library <libraries/sessions>` didn't take into account ``session.hash_bits_per_character`` when validating session IDs.
 -  Fixed a bug (#4871) - :doc:`Query Builder <database/query_builder>` method ``update_batch()`` didn't properly handle identifier escaping.
 -  Fixed a bug (#4884) - :doc:`Query Builder <database/query_builder>` didn't properly parse field names ending in 'is' when used inside WHERE and HAVING statements.
--  Fixed a bug where ``CI_Log``, ``CI_Output``, ``CI_Email`` and ``CI_Zip`` didn't handle strings in a byte-safe manner when ``mbstring.func_override`` is enabled.
+-  Fixed a bug where ``CI_Log``, ``CI_Output``, ``CI_Email`` and ``CI_Zip`` didn't handle strings in a byte-safe manner when ``mbstring.func_overload`` is enabled.
 
 Version 3.1.1
 =============
@@ -119,7 +126,7 @@
 -  Fixed a bug where :doc:`Query Builder <database/query_builder>` method ``insert_batch()`` tried to execute an unsupported SQL query with the 'ibase' and 'pdo/firebird' drivers.
 -  Fixed a bug (#4809) - :doc:`Database <database/index>` driver 'pdo/mysql' didn't turn off ``AUTOCOMMIT`` when starting a transaction.
 -  Fixed a bug (#4822) - :doc:`CAPTCHA Helper <helpers/captcha_helper>` didn't clear expired PNG images.
--  Fixed a bug (#4823) - :doc:`Session Library <libraries/sessions>` 'files' driver could enter an infinite loop if ``mbstring.func_override`` is enabled.
+-  Fixed a bug (#4823) - :doc:`Session Library <libraries/sessions>` 'files' driver could enter an infinite loop if ``mbstring.func_overload`` is enabled.
 -  Fixed a bug (#4851) - :doc:`Database Forge <database/forge>` didn't quote schema names passed to its ``create_database()`` method.
 -  Fixed a bug (#4863) - :doc:`HTML Table Library <libraries/table>` method ``set_caption()`` was missing method chaining support.
 -  Fixed a bug (#4843) - :doc:`XML-RPC Library <libraries/xmlrpc>` client class didn't set a read/write socket timeout.