diff --git a/dev/boot.js b/dev/boot.js
index f8c9ac381..a60a14e66 100644
--- a/dev/boot.js
+++ b/dev/boot.js
@@ -16,12 +16,14 @@ const
 		toggle(div);
 	},
 
-	loadScript = src => src ? new Promise((resolve, reject) => {
+	loadScript = (src, integrity) => src ? new Promise((resolve, reject) => {
 			const script = doc.createElement('script');
 			script.onload = () => resolve();
 			script.onerror = () => reject('Failed loading ' + src);
 			script.src = src;
 //			script.async = true;
+//			script.crossorigin = ''; // same as 'anonymous'
+			if (integrity) { script.integrity = integrity; }
 			doc.head.append(script);
 		}) : Promise.reject('src is empty');
 
@@ -146,8 +148,8 @@ if (!navigator.cookieEnabled) {
 		RL_APP_DATA = appData;
 		const url = appData.StaticLibsJs,
 			cb = () => rl.app.bootstart();
-		loadScript(url)
-			.then(() => loadScript(url.replace('/libs.', `/${admin?'admin':'app'}.`)))
+		loadScript(url, appData.StaticLibsJsSri)
+			.then(() => loadScript(url.replace('/libs.', `/${admin?'admin':'app'}.`), appData.StaticAppJsSri))
 			.then(() => appData.PluginsLink ? loadScript(qUri(appData.PluginsLink)) : Promise.resolve())
 			.then(() => rl.app
 				? cb()
diff --git a/gulpfile.js b/gulpfile.js
index 9b0d1bbb4..4bfa5b8d7 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -5,17 +5,19 @@ const { cleanStatic } = require('./tasks/common');
 const { js, jsLint } = require('./tasks/js');
 const { css, cssLint } = require('./tasks/css');
 const { vendors } = require('./tasks/vendors');
+const { sri } = require('./tasks/sri');
 
 const clean = gulp.series(cleanStatic);
 
 const lint = gulp.parallel(jsLint, cssLint);
 
 const buildState1 = gulp.parallel(js, css, vendors);
-const buildState2 = gulp.series(clean, buildState1);
+const buildState2 = gulp.series(clean, buildState1, sri);
 
 const build = gulp.parallel(lint, buildState2);
 
 exports.css = css;
 exports.lint = lint;
+exports.sri = sri;
 exports.build = build;
 exports.default = build;
diff --git a/snappymail/v/0.0.0/app/libraries/RainLoop/Actions.php b/snappymail/v/0.0.0/app/libraries/RainLoop/Actions.php
index 0e39503f9..598170540 100644
--- a/snappymail/v/0.0.0/app/libraries/RainLoop/Actions.php
+++ b/snappymail/v/0.0.0/app/libraries/RainLoop/Actions.php
@@ -779,6 +779,12 @@ class Actions
 		$aResult['StaticLibsJs'] = Utils::WebStaticPath('js/' . ($bAppJsDebug ? '' : 'min/') .
 			'libs' . ($bAppJsDebug ? '' : '.min') . '.js');
 
+		if (!$bAppJsDebug) {
+			$aSri = \SnappyMail\Integrity::loadSriHashes();
+			$aResult['StaticLibsJsSri'] = $aSri['libs.min.js'] ?? '';
+			$aResult['StaticAppJsSri'] = $aSri[($bAdmin ? 'admin' : 'app') . '.min.js'] ?? '';
+		}
+
 		$this->oPlugins->InitAppData($bAdmin, $aResult, $oAccount);
 
 		return $aResult;
diff --git a/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php b/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
index 52104cf80..461aef273 100644
--- a/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
+++ b/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
@@ -207,9 +207,12 @@ abstract class Service
 			if ($sResult) {
 				$sResult .= '<!--cached-->';
 			} else {
+				$aSri = $sAppCssMin ? \SnappyMail\Integrity::loadSriHashes() : [];
+				$sCssFile = ($bAdmin ? 'admin' : 'app').$sAppCssMin.'.css';
 				$aTemplateParameters['{{BaseAppBootCss}}'] = \file_get_contents(APP_VERSION_ROOT_PATH.'static/css/boot'.$sAppCssMin.'.css');
 				$aTemplateParameters['{{BaseAppBootScript}}'] = \file_get_contents(APP_VERSION_ROOT_PATH.'static/js'.($sAppJsMin ? '/min' : '').'/boot'.$sAppJsMin.'.js');
-				$aTemplateParameters['{{BaseAppMainCssLink}}'] = Utils::WebStaticPath('css/'.($bAdmin ? 'admin' : 'app').$sAppCssMin.'.css');
+				$aTemplateParameters['{{BaseAppMainCssLink}}'] = Utils::WebStaticPath('css/'.$sCssFile);
+				$aTemplateParameters['{{BaseAppMainCssSri}}'] = empty($aSri[$sCssFile]) ? '' : ' integrity="'.$aSri[$sCssFile].'"';
 				$aTemplateParameters['{{BaseAppThemeCss}}'] = \preg_replace('/\\s*([:;{},]+)\\s*/s', '$1', $oActions->compileCss($sThemeName, $bAdmin));
 				$aTemplateParameters['{{BaseLanguage}}'] = $oActions->compileLanguage($sLanguage, $bAdmin);
 				$aTemplateParameters['{{BaseTemplates}}'] = Utils::ClearHtmlOutput($oServiceActions->compileTemplates($bAdmin));
diff --git a/snappymail/v/0.0.0/app/libraries/snappymail/integrity.php b/snappymail/v/0.0.0/app/libraries/snappymail/integrity.php
index 97873d50c..6f0ff3447 100644
--- a/snappymail/v/0.0.0/app/libraries/snappymail/integrity.php
+++ b/snappymail/v/0.0.0/app/libraries/snappymail/integrity.php
@@ -8,7 +8,7 @@ abstract class Integrity
 	/**
 	 * Called by https://webmail.tld/?/Test
 	 */
-	public static function test()
+	public static function test(): void
 	{
 		$result = static::phpVersion();
 		if ($result) {
@@ -89,14 +89,15 @@ abstract class Integrity
 		}
 	}
 
-	public static function phpVersion()
+	public static function phpVersion(): ?string
 	{
 		if (PHP_VERSION_ID < 80200) {
 			return 'Your PHP version ('.PHP_VERSION.') is lower than the minimal required 8.2.0!';
 		}
+		return null;
 	}
 
-	public static function phpExtensions()
+	public static function phpExtensions(): array
 	{
 		$aRequirements = array(
 			'openssl'  => extension_loaded('openssl'),
@@ -123,4 +124,23 @@ abstract class Integrity
 		return $aMissing;
 	}
 
+	// https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Subresource_Integrity
+	private static $aSri;
+	public static function loadSriHashes(): array
+	{
+		if (!\is_array($aSri)) {
+			$sSriPath = APP_VERSION_ROOT_PATH . 'static/sri.json';
+			$aSri = \is_readable($sSriPath) ? \json_decode(\file_get_contents($sSriPath), true) : [];
+			if (!$aSri) {
+				$aSri = [
+					'libs.min.js'   => \hash_file('sha384', APP_VERSION_ROOT_PATH . 'static/js/min/libs.min.js'),
+					'admin.min.js'  => \hash_file('sha384', APP_VERSION_ROOT_PATH . 'static/js/min/admin.min.js'),
+					'app.min.js'    => \hash_file('sha384', APP_VERSION_ROOT_PATH . 'static/js/min/app.min.js'),
+					'admin.min.css' => \hash_file('sha384', APP_VERSION_ROOT_PATH . 'static/css/admin.min.css'),
+					'app.min.css'   => \hash_file('sha384', APP_VERSION_ROOT_PATH . 'static/css/app.min.css'),
+				];
+			}
+		}
+		return $aSri;
+	}
 }
diff --git a/snappymail/v/0.0.0/app/templates/Index.html b/snappymail/v/0.0.0/app/templates/Index.html
index bd5c60d07..8970039ec 100644
--- a/snappymail/v/0.0.0/app/templates/Index.html
+++ b/snappymail/v/0.0.0/app/templates/Index.html
@@ -9,7 +9,7 @@
 	<meta name="theme-color" content="black">
 	<title></title>
 	<style id="app-boot-css">{{BaseAppBootCss}}</style>
-	<link type="text/css" rel="stylesheet" href="{{BaseAppMainCssLink}}">
+	<link type="text/css" rel="stylesheet" href="{{BaseAppMainCssLink}}{{BaseAppMainCssSri}}">
 	<link rel="manifest" href="{{BaseAppManifestLink}}">
 	<link rel="icon" href="{{BaseFavIconSvg}}" type="image/svg+xml">
 	<style id="app-theme-style" data-name="{{BaseAppThemeName}}">{{BaseAppThemeCss}}</style>
diff --git a/tasks/sri.js b/tasks/sri.js
new file mode 100644
index 000000000..eef5e8b63
--- /dev/null
+++ b/tasks/sri.js
@@ -0,0 +1,39 @@
+/* Tachyon Webmail (c) Tachyon | Licensed under AGPL v3 */
+const fs = require('fs');
+const crypto = require('crypto');
+const path = require('path');
+
+const { config } = require('./config');
+
+function sriHash(filePath) {
+	const data = fs.readFileSync(filePath);
+	const hash = crypto.createHash('sha384').update(data).digest('base64');
+	return 'sha384-' + hash;
+}
+
+function sri(done) {
+	const jsMinDir = config.paths.staticMinJS;
+	const cssDir = config.paths.staticCSS;
+
+	const files = [
+		['libs.min.js',  jsMinDir + 'libs.min.js'],
+		['app.min.js',   jsMinDir + 'app.min.js'],
+		['admin.min.js', jsMinDir + 'admin.min.js'],
+		['app.min.css',  cssDir + 'app.min.css'],
+		['admin.min.css',cssDir + 'admin.min.css'],
+	];
+
+	const hashes = {};
+	for (const [key, filePath] of files) {
+		if (fs.existsSync(filePath)) {
+			hashes[key] = sriHash(filePath);
+		}
+	}
+
+	const outPath = path.join('snappymail/v/' + config.devVersion, 'static/sri.json');
+	fs.writeFileSync(outPath, JSON.stringify(hashes, null, '\t') + '\n');
+	console.log('[sri] wrote ' + outPath);
+	done();
+}
+
+exports.sri = sri;