diff --git a/core/includes/session.inc b/core/includes/session.inc
index fa46972..fd2b1ec 100644
--- a/core/includes/session.inc
+++ b/core/includes/session.inc
@@ -92,19 +92,21 @@ function _drupal_session_read($sid) {
   // Otherwise, if the session is still active, we have a record of the
   // client's session in the database. If it's HTTPS then we are either have
   // a HTTPS session or we are about to log in so we check the sessions table
-  // for an anonymous session with the non-HTTPS-only cookie.
+  // for an anonymous session with the non-HTTPS-only cookie. The session ID
+  // that is in the user's cookie is hashed before being stored in the database
+  // as a security measure. Thus, we have to hash it to match the database.
   if (\Drupal::request()->isSecure()) {
-    $values = db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.ssid = :ssid", array(':ssid' => $sid))->fetchAssoc();
+    $values = db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.ssid = :ssid", array(':ssid' => Crypt::hashBase64($sid)))->fetchAssoc();
     if (!$values) {
       if ($cookies->has($insecure_session_name)) {
         $values = db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = :sid AND s.uid = 0", array(
-        ':sid' => $cookies->get($insecure_session_name)))
+        ':sid' => Crypt::hashBase64($cookies->get($insecure_session_name))))
         ->fetchAssoc();
       }
     }
   }
   else {
-    $values = db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = :sid", array(':sid' => $sid))->fetchAssoc();
+    $values = db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = :sid", array(':sid' => Crypt::hashBase64($sid)))->fetchAssoc();
   }
 
   // We found the client's session record and they are an authenticated,
@@ -185,18 +187,19 @@ function _drupal_session_write($sid, $value) {
       // Use the session ID as 'sid' and an empty string as 'ssid' by default.
       // _drupal_session_read() does not allow empty strings so that's a safe
       // default.
-      $key = array('sid' => $sid, 'ssid' => '');
+      $key = array('sid' => Crypt::hashBase64($sid), 'ssid' => '');
       // On HTTPS connections, use the session ID as both 'sid' and 'ssid'.
       if (\Drupal::request()->isSecure()) {
-        $key['ssid'] = $sid;
+        $key['ssid'] = Crypt::hashBase64($sid);
         $cookies = \Drupal::request()->cookies;
         // The "secure pages" setting allows a site to simultaneously use both
         // secure and insecure session cookies. If enabled and both cookies are
-        // presented then use both keys.
+        // presented then use both keys. The session ID from the cookie is
+        // hashed before being stored in the database as a security measure.
         if (settings()->get('mixed_mode_sessions', FALSE)) {
           $insecure_session_name = substr(session_name(), 1);
           if ($cookies->has($insecure_session_name)) {
-            $key['sid'] = $cookies->get($insecure_session_name);
+            $key['sid'] = Crypt::hashBase64($cookies->get($insecure_session_name));
           }
         }
       }
@@ -384,18 +387,18 @@ function drupal_session_regenerate() {
     $params = session_get_cookie_params();
     $expire = $params['lifetime'] ? REQUEST_TIME + $params['lifetime'] : 0;
     setcookie(session_name(), session_id(), $expire, $params['path'], $params['domain'], $params['secure'], $params['httponly']);
-    $fields = array('sid' => session_id());
+    $fields = array('sid' => Crypt::hashBase64(session_id()));
     if ($is_https) {
-      $fields['ssid'] = session_id();
+      $fields['ssid'] = Crypt::hashBase64(session_id());
       // If the "secure pages" setting is enabled, use the newly-created
       // insecure session identifier as the regenerated sid.
       if (settings()->get('mixed_mode_sessions', FALSE)) {
-        $fields['sid'] = $session_id;
+        $fields['sid'] = Crypt::hashBase64($session_id);
       }
     }
     db_update('sessions')
       ->fields($fields)
-      ->condition($is_https ? 'ssid' : 'sid', $old_session_id)
+      ->condition($is_https ? 'ssid' : 'sid', Crypt::hashBase64($old_session_id))
       ->execute();
   }
   elseif (isset($old_insecure_session_id)) {
@@ -403,8 +406,8 @@ function drupal_session_regenerate() {
     // secure site but a session was active on the insecure site, update the
     // insecure session with the new session identifiers.
     db_update('sessions')
-      ->fields(array('sid' => $session_id, 'ssid' => session_id()))
-      ->condition('sid', $old_insecure_session_id)
+      ->fields(array('sid' => Crypt::hashBase64($session_id), 'ssid' => Crypt::hashBase64(session_id())))
+      ->condition('sid', Crypt::hashBase64($old_insecure_session_id))
       ->execute();
   }
   else {
@@ -437,7 +440,7 @@ function _drupal_session_destroy($sid) {
   $is_https = \Drupal::request()->isSecure();
   // Delete session data.
   db_delete('sessions')
-    ->condition($is_https ? 'ssid' : 'sid', $sid)
+    ->condition($is_https ? 'ssid' : 'sid', Crypt::hashBase64($sid))
     ->execute();
 
   // Reset $_SESSION and $user to prevent a new session from being started
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 265012e..30d68c2 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -661,8 +661,9 @@ protected function drupalUserIsLoggedIn($account) {
     if (!isset($account->session_id)) {
       return FALSE;
     }
-    // @see _drupal_session_read()
-    return (bool) db_query("SELECT sid FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = :sid", array(':sid' => $account->session_id))->fetchField();
+    // @see _drupal_session_read(). The session ID is hashed before being stored
+    // in the database.
+    return (bool) db_query("SELECT sid FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = :sid", array(':sid' => Crypt::hashBase64($account->session_id)))->fetchField();
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php b/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
index 87cd97b..cf19217 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Session/SessionHttpsTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\simpletest\WebTestBase;
 use Symfony\Component\HttpFoundation\Request;
+use Drupal\Component\Utility\Crypt;
 
 /**
  * Ensure that when running under HTTPS two session cookies are generated.
@@ -229,8 +230,8 @@ protected function testHttpsSession() {
    */
   protected function assertSessionIds($sid, $ssid, $assertion_text) {
     $args = array(
-      ':sid' => $sid,
-      ':ssid' => $ssid,
+      ':sid' => Crypt::hashBase64($sid),
+      ':ssid' => Crypt::hashBase64($ssid),
     );
     return $this->assertTrue(db_query('SELECT timestamp FROM {sessions} WHERE sid = :sid AND ssid = :ssid', $args)->fetchField(), $assertion_text);
   }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 7d121af..e3bdcc7 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1048,13 +1048,13 @@ function system_schema() {
         'not null' => TRUE,
       ),
       'sid' => array(
-        'description' => "A session ID. The value is generated by Drupal's session handlers.",
+        'description' => "A session ID (hashed). The value is generated by Drupal's session handlers.",
         'type' => 'varchar',
         'length' => 128,
         'not null' => TRUE,
       ),
       'ssid' => array(
-        'description' => "Secure session ID. The value is generated by Drupal's session handlers.",
+        'description' => "Secure session ID (hashed). The value is generated by Drupal's session handlers.",
         'type' => 'varchar',
         'length' => 128,
         'not null' => TRUE,