diff --git a/MD_JAIL.php b/MD_JAIL.php
new file mode 100644
index 0000000..6199214
--- /dev/null
+++ b/MD_JAIL.php
@@ -0,0 +1,156 @@
+<?PHP
+/**
+ * Provides class MD_JAIL.
+ */
+declare(strict_types = 1);
+
+/**
+ * A class that, once initialized, forces the programmer to make security instructions implicit.
+ * If an object of the class has been created, not specifying security instructions
+ * leads to an error.
+ * A restriction on basic file operations is not practical in an md context because of
+ * the way transations are loaded through MDTlLoader.
+ */
+final class MD_JAIL {
+
+    const STATUS_NONE      = 0;
+    const STATUS_STARTED   = 1;
+    const STATUS_SPECIFIED = 2; // Determines that everything is fine.
+
+    /** @var integer */
+    private int $_status = self::STATUS_NONE;
+
+    /**
+     * @var integer
+     * Maximum execution time in seconds.
+     */
+    public int $max_execution_time;
+
+    /**
+     * @var string[]
+     * Specifies which paths may be used by this script.
+     */
+    private array $_open_basedir = [];
+
+    /**
+     * @var string
+     * Specifies the maximum RAM the script may use.
+     */
+    public string $memory_limit;
+
+    /**
+     * Registers an additional accessible directory for open_basedir.
+     *
+     * @param string $dir Directory to register.
+     *
+     * @return void
+     */
+    public function register_accessible_dir(string $dir):void {
+
+        $this->_open_basedir[] = $dir;
+
+    }
+
+    /**
+     * Applies the memory limit setting.
+     *
+     * @return void
+     */
+    private function _apply_memory_limit():void {
+
+        if (!isset($this->memory_limit)) {
+            throw new MDJailSecurityOptionNotSetException("It has not been specified, which memory limit the script should hold. Set MD_JAIL->memory_limit = string.");
+        }
+        if (ini_set("memory_limit", $this->memory_limit) === false) {
+            throw new Exception('Failed to change memory_limit to ' . $this->memory_limit);
+        }
+
+    }
+
+    /**
+     * Applies the maximum execution time setting.
+     *
+     * @return void
+     */
+    private function _apply_time_limit():void {
+
+        if (!isset($this->max_execution_time)) {
+            throw new MDJailSecurityOptionNotSetException("It has not been specified, which maximum execution time the script should hold. Set MD_JAIL->max_execution_time = integer.");
+        }
+        if (set_time_limit($this->max_execution_time) === false) {
+            throw new Exception('Failed to change max_execution_time to ' . $this->max_execution_time);
+        }
+
+    }
+
+    /**
+     * Applies basedir restrictions.
+     *
+     * @return void
+     */
+     private function _apply_basedir_restriction():void {
+
+        if (empty($this->_open_basedir)) {
+            throw new MDJailSecurityOptionNotSetException("It has not been specified, which memory limit the script should hold. Set MD_JAIL->open_basedir = string.");
+        }
+        if (ini_set("open_basedir", implode(':', $this->_open_basedir)) === false) {
+            throw new Exception('Failed to set open_basedir restrictions');
+        }
+
+     }
+
+    /**
+     * Enforces security options previously set.
+     *
+     * @return void
+     */
+    public function enforce():void {
+
+        $this->_apply_memory_limit();
+        $this->_apply_time_limit();
+
+        // Set accessible file paths
+        // $this->_apply_basedir_restriction();
+
+        $this->_status = self::STATUS_SPECIFIED;
+        $this->__destruct();
+
+    }
+
+    /**
+     * Setup function. Registers a shutdown function that throws an error
+     * if the security specifications have not been made.
+     *
+     * @return void
+     */
+    public function __construct() {
+
+        $this->_status = self::STATUS_STARTED;
+
+    }
+
+    public function __destruct() {
+
+        if ($this->_status !== self::STATUS_SPECIFIED) {
+
+            echo "Security specifications need to be set.";
+
+            if (!isset($this->memory_limit)) {
+                echo "Set memory limit";
+            }
+
+            if (!isset($this->max_execution_time)) {
+                echo "Set max_execution_time";
+            }
+
+            if (empty($this->_open_basedir)) {
+                echo "Set open_basedir";
+            }
+
+            throw new MDJailSecurityOptionNotSetException("Security specifications need to be set.");
+        }
+
+    }
+
+}
+
diff --git a/exceptions/MDJailSecurityOptionNotSetException.php b/exceptions/MDJailSecurityOptionNotSetException.php
new file mode 100644
index 0000000..eaa33e8
--- /dev/null
+++ b/exceptions/MDJailSecurityOptionNotSetException.php
@@ -0,0 +1,21 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Exception thrown by MDJail if a required security option has not been set.
+ */
+final class MDJailSecurityOptionNotSetException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'A security option of MD_JAIL has not been set: <b>' . $this->getMessage() . '</b>).';
+        return $errorMsg;
+
+    }
+
+}