Index: gnome-shell-40.rc/data/gnome-shell-theme.gresource.xml
===================================================================
--- gnome-shell-40.rc.orig/data/gnome-shell-theme.gresource.xml
+++ gnome-shell-40.rc/data/gnome-shell-theme.gresource.xml
@@ -16,6 +16,7 @@
     <file alias="icons/scalable/status/message-indicator-symbolic.svg">message-indicator-symbolic.svg</file>
     <file>no-events.svg</file>
     <file>no-notifications.svg</file>
+    <file>noise-texture.png</file>
     <file>pad-osd.css</file>
     <file alias="icons/scalable/status/eye-open-negative-filled-symbolic.svg">eye-open-negative-filled-symbolic.svg</file>
     <file alias="icons/scalable/status/eye-not-looking-symbolic.svg">eye-not-looking-symbolic.svg</file>
Index: gnome-shell-40.rc/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
===================================================================
--- gnome-shell-40.rc.orig/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
+++ gnome-shell-40.rc/data/theme/gnome-shell-sass/widgets/_screen-shield.scss
@@ -65,6 +65,11 @@
   box-shadow: 0px 2px 4px rgba(0,0,0,0.6);
 }
 
+.bgLockDialogGroup-background {
+  border: none;
+  background-color: transparent;
+}
+
 #lockDialogGroup {
   background-color: $system_bg_color;
 }
Index: gnome-shell-40.rc/js/ui/screenShield.js
===================================================================
--- gnome-shell-40.rc.orig/js/ui/screenShield.js
+++ gnome-shell-40.rc/js/ui/screenShield.js
@@ -4,6 +4,7 @@ const { AccountsService, Clutter, Gio,
         GLib, Graphene, Meta, Shell, St } = imports.gi;
 const Signals = imports.signals;
 
+const Background = imports.ui.background;
 const GnomeSession = imports.misc.gnomeSession;
 const OVirt = imports.gdm.oVirt;
 const LoginManager = imports.misc.loginManager;
@@ -16,6 +17,8 @@ const SmartcardManager = imports.misc.sm
 
 const { adjustAnimationTime } = imports.ui.environment;
 
+const LOCKDIALOG_BACKGROUND_SCHEMA = 'org.gnome.desktop.background.lockdialog';
+
 const SCREENSAVER_SCHEMA = 'org.gnome.desktop.screensaver';
 const LOCK_ENABLED_KEY = 'lock-enabled';
 const LOCK_DELAY_KEY = 'lock-delay';
@@ -25,6 +28,9 @@ const DISABLE_LOCK_KEY = 'disable-lock-s
 
 const LOCKED_STATE_STR = 'screenShield.locked';
 
+const BLUR_BRIGHTNESS = 0.55;
+const BLUR_SIGMA = 60;
+
 // ScreenShield animation time
 // - STANDARD_FADE_TIME is used when the session goes idle
 // - MANUAL_FADE_TIME is used for lowering the shield when asked by the user,
@@ -65,6 +71,16 @@ var ScreenShield = class {
             name: 'lockDialogGroup',
         });
 
+        // Add background for this._lockDialogGroup
+        this._bgLockDialogGroup = new Clutter.Actor();
+        this._lockDialogGroup.add_actor(this._bgLockDialogGroup);
+        this._lockDialogGroup.set_child_below_sibling(this._bgLockDialogGroup, null);
+        this._bgManagersLockDialogGroup = [];
+
+        this._updateBgLockDialogGroup();
+        this._monitorsChangedId =
+            Main.layoutManager.connect('monitors-changed', this._updateBgLockDialogGroup.bind(this));
+
         this.actor.add_actor(this._lockScreenGroup);
         this.actor.add_actor(this._lockDialogGroup);
 
@@ -142,6 +158,15 @@ var ScreenShield = class {
         this._cursorTracker = Meta.CursorTracker.get_for_display(global.display);
 
         this._syncInhibitor();
+
+        this.connect('destroy', this._onDestroy.bind(this));
+    }
+
+    _onDestroy() {
+        if (this._monitorsChangedId) {
+            Main.layoutManager.disconnect(this._monitorsChangedId);
+            delete this._monitorsChangedId;
+        }
     }
 
     _setActive(active) {
@@ -492,6 +517,53 @@ var ScreenShield = class {
         this.emit('wake-up-screen');
     }
 
+    _createBgLockDialogGroup(monitorIndex) {
+        let monitor = Main.layoutManager.monitors[monitorIndex];
+        let widget = new St.Widget({
+            style_class: 'bgLockDialogGroup-background',
+            x: monitor.x,
+            y: monitor.y,
+            width: monitor.width,
+            height: monitor.height,
+        });
+
+        let bgManager = new Background.BackgroundManager({
+            container: widget,
+            monitorIndex,
+            controlPosition: false,
+            settingsSchema: LOCKDIALOG_BACKGROUND_SCHEMA
+        });
+
+        this._bgManagersLockDialogGroup.push(bgManager);
+
+        this._bgLockDialogGroup.add_child(widget);
+
+        const themeContext = St.ThemeContext.get_for_stage(global.stage);
+
+        let effect = new Shell.BlurEffect({
+            brightness: BLUR_BRIGHTNESS,
+            sigma: BLUR_SIGMA * themeContext.scale_factor,
+        });
+
+        this._scaleChangedId = themeContext.connect('notify::scale-factor', () => {
+            effect.sigma = BLUR_SIGMA * themeContext.scale_factor;
+        });
+
+        widget.add_effect(effect);
+    }
+
+    _updateBgLockDialogGroup() {
+        for (let i = 0; i < this._bgManagersLockDialogGroup.length; i++)
+            this._bgManagersLockDialogGroup[i].destroy();
+
+        this._bgManagersLockDialogGroup = [];
+        this._bgLockDialogGroup.destroy_all_children();
+
+        for (let i = 0; i < Main.layoutManager.monitors.length; i++)
+            this._createBgLockDialogGroup(i);
+    }
+
+
     get locked() {
         return this._isLocked;
     }