feat:Add Dual Layer Server-Side Encryption via DSSE-KMS

apps/dav/composer/composer/autoload_static.php

@@ -7,14 +7,14 @@
 class ComposerStaticInitDAV
 {
     public static $prefixLengthsPsr4 = array (
-        'O' => 
+        'O' =>
         array (
             'OCA\\DAV\\' => 8,
         ),
     );
 
     public static $prefixDirsPsr4 = array (
-        'OCA\\DAV\\' => 
+        'OCA\\DAV\\' =>
         array (
             0 => __DIR__ . '/..' . '/../lib',
         ),

apps/settings/composer/composer/autoload_classmap.php

@@ -132,6 +132,7 @@
     'OCA\\Settings\\SetupChecks\\RandomnessSecure' => $baseDir . '/../lib/SetupChecks/RandomnessSecure.php',
     'OCA\\Settings\\SetupChecks\\ReadOnlyConfig' => $baseDir . '/../lib/SetupChecks/ReadOnlyConfig.php',
     'OCA\\Settings\\SetupChecks\\RepairSanitizeSystemTagsAvailable' => $baseDir . '/../lib/SetupChecks/RepairSanitizeSystemTagsAvailable.php',
+    'OCA\\Settings\\SetupChecks\\S3SseCEncryption' => $baseDir . '/../lib/SetupChecks/S3SseCEncryption.php',
     'OCA\\Settings\\SetupChecks\\SchedulingTableSize' => $baseDir . '/../lib/SetupChecks/SchedulingTableSize.php',
     'OCA\\Settings\\SetupChecks\\SecurityHeaders' => $baseDir . '/../lib/SetupChecks/SecurityHeaders.php',
     'OCA\\Settings\\SetupChecks\\ServerIdConfig' => $baseDir . '/../lib/SetupChecks/ServerIdConfig.php',

apps/settings/composer/composer/autoload_static.php

@@ -147,6 +147,7 @@ class ComposerStaticInitSettings
         'OCA\\Settings\\SetupChecks\\RandomnessSecure' => __DIR__ . '/..' . '/../lib/SetupChecks/RandomnessSecure.php',
         'OCA\\Settings\\SetupChecks\\ReadOnlyConfig' => __DIR__ . '/..' . '/../lib/SetupChecks/ReadOnlyConfig.php',
         'OCA\\Settings\\SetupChecks\\RepairSanitizeSystemTagsAvailable' => __DIR__ . '/..' . '/../lib/SetupChecks/RepairSanitizeSystemTagsAvailable.php',
+        'OCA\\Settings\\SetupChecks\\S3SseCEncryption' => __DIR__ . '/..' . '/../lib/SetupChecks/S3SseCEncryption.php',
         'OCA\\Settings\\SetupChecks\\SchedulingTableSize' => __DIR__ . '/..' . '/../lib/SetupChecks/SchedulingTableSize.php',
         'OCA\\Settings\\SetupChecks\\SecurityHeaders' => __DIR__ . '/..' . '/../lib/SetupChecks/SecurityHeaders.php',
         'OCA\\Settings\\SetupChecks\\ServerIdConfig' => __DIR__ . '/..' . '/../lib/SetupChecks/ServerIdConfig.php',

apps/settings/lib/AppInfo/Application.php

@@ -69,6 +69,7 @@
 use OCA\Settings\SetupChecks\RandomnessSecure;
 use OCA\Settings\SetupChecks\ReadOnlyConfig;
 use OCA\Settings\SetupChecks\RepairSanitizeSystemTagsAvailable;
+use OCA\Settings\SetupChecks\S3SseCEncryption;
 use OCA\Settings\SetupChecks\SchedulingTableSize;
 use OCA\Settings\SetupChecks\SecurityHeaders;
 use OCA\Settings\SetupChecks\ServerIdConfig;
@@ -212,6 +213,7 @@ public function register(IRegistrationContext $context): void {
 		$context->registerSetupCheck(RandomnessSecure::class);
 		$context->registerSetupCheck(ReadOnlyConfig::class);
 		$context->registerSetupCheck(RepairSanitizeSystemTagsAvailable::class);
+		$context->registerSetupCheck(S3SseCEncryption::class);
 		$context->registerSetupCheck(SecurityHeaders::class);
 		$context->registerSetupCheck(ServerIdConfig::class);
 		$context->registerSetupCheck(SchedulingTableSize::class);

apps/settings/lib/SetupChecks/S3SseCEncryption.php

@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Settings\SetupChecks;
+
+use OCP\IConfig;
+use OCP\IL10N;
+use OCP\IURLGenerator;
+use OCP\SetupCheck\ISetupCheck;
+use OCP\SetupCheck\SetupResult;
+
+/**
+ * Warns when the primary or multibucket S3 object store is configured to use SSE-C
+ * (customer-provided key) server-side encryption, deprecated since Nextcloud 34.
+ *
+ * Not to be confused with LegacySSEKeyFormat, which checks Nextcloud's own
+ * server-side-encryption app's legacy key file format and is unrelated to S3.
+ */
+class S3SseCEncryption implements ISetupCheck {
+	public function __construct(
+		private IL10N $l10n,
+		private IConfig $config,
+		private IURLGenerator $urlGenerator,
+	) {
+	}
+
+	#[\Override]
+	public function getName(): string {
+		return $this->l10n->t('S3 SSE-C encryption');
+	}
+
+	#[\Override]
+	public function getCategory(): string {
+		return 'security';
+	}
+
+	/**
+	 * @param array $arguments the 'arguments' of an 'objectstore'/'objectstore_multibucket' config
+	 */
+	private function isSseCInEffect(array $arguments): bool {
+		$sse = $arguments['sse'] ?? '';
+		if ($sse !== '') {
+			return $sse === 'sse-c';
+		}
+
+		// No explicit 'sse' argument: matches the precedence in
+		// OC\Files\ObjectStore\S3ConnectionTrait::parseEncryptionParams() -- the legacy
+		// 'sse_c_key' argument wins over 'sse_kms_enabled' whenever both are set.
+		return !empty($arguments['sse_c_key']);
+	}
+
+	#[\Override]
+	public function run(): SetupResult {
+		foreach (['objectstore', 'objectstore_multibucket'] as $key) {
+			$objectStore = $this->config->getSystemValue($key, null);
+			if (!is_array($objectStore) || ($objectStore['class'] ?? null) !== 'OC\\Files\\ObjectStore\\S3') {
+				continue;
+			}
+
+			if ($this->isSseCInEffect($objectStore['arguments'] ?? [])) {
+				return SetupResult::warning(
+					$this->l10n->t('This instance uses S3 SSE-C (customer-provided key) encryption, deprecated since Nextcloud 34: Amazon S3 disabled SSE-C by default for new buckets in April 2026. Migrate to SSE-KMS instead.'),
+					$this->urlGenerator->linkToDocs('admin-s3-sse-c'),
+				);
+			}
+		}
+
+		return SetupResult::success($this->l10n->t('No deprecated S3 SSE-C encryption configuration found.'));
+	}
+}

apps/settings/tests/SetupChecks/S3SseCEncryptionTest.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Settings\Tests\SetupChecks;
+
+use OCA\Settings\SetupChecks\S3SseCEncryption;
+use OCP\IConfig;
+use OCP\IL10N;
+use OCP\IURLGenerator;
+use OCP\SetupCheck\SetupResult;
+use PHPUnit\Framework\MockObject\MockObject;
+use Test\TestCase;
+
+class S3SseCEncryptionTest extends TestCase {
+	private IL10N&MockObject $l10n;
+	private IConfig&MockObject $config;
+	private IURLGenerator&MockObject $urlGenerator;
+
+	#[\Override]
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->l10n = $this->createMock(IL10N::class);
+		$this->l10n->method('t')
+			->willReturnCallback(function ($message, array $replace = []) {
+				return vsprintf($message, $replace);
+			});
+		$this->config = $this->createMock(IConfig::class);
+		$this->urlGenerator = $this->createMock(IURLGenerator::class);
+	}
+
+	public static function dataRun(): array {
+		$s3 = static fn (array $arguments): array => ['class' => 'OC\\Files\\ObjectStore\\S3', 'arguments' => $arguments];
+
+		return [
+			'no objectstore configured' => [null, null, SetupResult::SUCCESS],
+			'non-S3 objectstore class' => [['class' => 'OC\\Files\\ObjectStore\\Swift', 'arguments' => ['sse_c_key' => 'x']], null, SetupResult::SUCCESS],
+			'S3 with no sse* arguments' => [$s3([]), null, SetupResult::SUCCESS],
+			'S3 with sse-kms' => [$s3(['sse' => 'sse-kms']), null, SetupResult::SUCCESS],
+			'S3 with sse-kms-dsse' => [$s3(['sse' => 'sse-kms-dsse']), null, SetupResult::SUCCESS],
+			'S3 with legacy sse_c_key only' => [$s3(['sse_c_key' => 'x']), null, SetupResult::WARNING],
+			'S3 with explicit sse => sse-c' => [$s3(['sse' => 'sse-c', 'sse_c_key' => 'x']), null, SetupResult::WARNING],
+			'S3 with both legacy keys set (sse_c_key wins by precedence)' => [$s3(['sse_c_key' => 'x', 'sse_kms_enabled' => true]), null, SetupResult::WARNING],
+			'S3 with explicit sse overriding legacy sse_c_key' => [$s3(['sse' => 'sse-kms', 'sse_c_key' => 'x']), null, SetupResult::SUCCESS],
+			'multibucket S3 with legacy sse_c_key only' => [null, $s3(['sse_c_key' => 'x']), SetupResult::WARNING],
+			'multibucket S3 with sse-kms' => [null, $s3(['sse' => 'sse-kms']), SetupResult::SUCCESS],
+		];
+	}
+
+	#[\PHPUnit\Framework\Attributes\DataProvider('dataRun')]
+	public function testRun(?array $objectStore, ?array $objectStoreMultibucket, string $expected): void {
+		$this->urlGenerator->method('linkToDocs')->willReturn('admin-s3-sse-c');
+
+		$this->config->method('getSystemValue')
+			->willReturnCallback(function (string $key, $default = null) use ($objectStore, $objectStoreMultibucket) {
+				return match ($key) {
+					'objectstore' => $objectStore ?? $default,
+					'objectstore_multibucket' => $objectStoreMultibucket ?? $default,
+					default => $default,
+				};
+			});
+
+		$check = new S3SseCEncryption($this->l10n, $this->config, $this->urlGenerator);
+
+		$result = $check->run();
+		$this->assertEquals($expected, $result->getSeverity());
+	}
+}

config/config.sample.php

@@ -2116,6 +2116,33 @@
 			// using Amazon S3 (or any other implementation that supports it) we recommend enabling it by using "when_supported".
 			'request_checksum_calculation' => 'when_required',
 			'response_checksum_validation' => 'when_required',
+			// optional: Server-side encryption of objects at rest.
+			// Valid values are:
+			//  - '' (default): no server-side encryption requested by Nextcloud
+			//  - 'sse-s3': S3-managed AES256 key
+			//  - 'sse-c': customer-provided key, see 'sse_c_key' below (deprecated, see below)
+			//  - 'sse-kms': single layer of AWS KMS-managed encryption
+			//  - 'sse-kms-dsse': dual layer of AWS KMS-managed encryption (DSSE-KMS), higher cost
+			//    and latency than 'sse-kms' but required by some compliance standards
+			// https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingKMSEncryption.html
+			// https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingDSSEncryption.html
+			'sse' => '',
+			// optional: customer-provided key for 'sse' => 'sse-c', base64 encoded.
+			// Deprecated since Nextcloud 34: Amazon S3 disabled SSE-C by default for new
+			// buckets in April 2026. Use 'sse' => 'sse-kms' or 'sse-kms-dsse' instead.
+			'sse_c_key' => '',
+			// optional: ARN of the AWS KMS key to use for 'sse-kms' / 'sse-kms-dsse'.
+			// If omitted, the bucket's default KMS key (or the AWS-managed 'aws/s3' key) is used.
+			// The key must be a symmetric key in the same AWS region as the bucket.
+			'sse_kms_key_id' => '',
+			// optional: 'sse-kms' / 'sse-kms-dsse' only. Additional AWS KMS encryption context,
+			// e.g. to scope key usage to a tenant via a matching kms:EncryptionContext condition
+			// on the key policy. This is stored alongside the object and visible in AWS CloudTrail,
+			// so it must not contain secrets.
+			'sse_kms_encryption_context' => [],
+			// optional: 'sse-kms' only, not supported for 'sse-kms-dsse'. Enables S3 Bucket Keys,
+			// which can reduce AWS KMS request costs by up to 99% for SSE-KMS.
+			'sse_kms_bucket_key' => false,
 		],
 	],
 

lib/composer/composer/autoload_classmap.php

@@ -1884,6 +1884,7 @@
     'OC\\Files\\ObjectStore\\S3' => $baseDir . '/lib/private/Files/ObjectStore/S3.php',
     'OC\\Files\\ObjectStore\\S3ConfigTrait' => $baseDir . '/lib/private/Files/ObjectStore/S3ConfigTrait.php',
     'OC\\Files\\ObjectStore\\S3ConnectionTrait' => $baseDir . '/lib/private/Files/ObjectStore/S3ConnectionTrait.php',
+    'OC\\Files\\ObjectStore\\S3EncryptionMode' => $baseDir . '/lib/private/Files/ObjectStore/S3EncryptionMode.php',
     'OC\\Files\\ObjectStore\\S3ObjectTrait' => $baseDir . '/lib/private/Files/ObjectStore/S3ObjectTrait.php',
     'OC\\Files\\ObjectStore\\S3Signature' => $baseDir . '/lib/private/Files/ObjectStore/S3Signature.php',
     'OC\\Files\\ObjectStore\\StorageObjectStore' => $baseDir . '/lib/private/Files/ObjectStore/StorageObjectStore.php',

lib/composer/composer/autoload_static.php

@@ -1925,6 +1925,7 @@ class ComposerStaticInit749170dad3f5e7f9ca158f5a9f04f6a2
         'OC\\Files\\ObjectStore\\S3' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3.php',
         'OC\\Files\\ObjectStore\\S3ConfigTrait' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3ConfigTrait.php',
         'OC\\Files\\ObjectStore\\S3ConnectionTrait' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3ConnectionTrait.php',
+        'OC\\Files\\ObjectStore\\S3EncryptionMode' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3EncryptionMode.php',
         'OC\\Files\\ObjectStore\\S3ObjectTrait' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3ObjectTrait.php',
         'OC\\Files\\ObjectStore\\S3Signature' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/S3Signature.php',
         'OC\\Files\\ObjectStore\\StorageObjectStore' => __DIR__ . '/../../..' . '/lib/private/Files/ObjectStore/StorageObjectStore.php',

lib/private/Files/ObjectStore/S3ConfigTrait.php

@@ -41,4 +41,16 @@ trait S3ConfigTrait {
 	private bool $useMultipartCopy = true;
 
 	protected int $retriesMaxAttempts;
+
+	protected S3EncryptionMode $sseMode = S3EncryptionMode::None;
+
+	protected ?string $sseKmsKeyId = null;
+
+	/** Already base64-encoded JSON, ready to hand to the AWS SDK */
+	protected ?string $sseKmsEncryptionContext = null;
+
+	protected bool $sseKmsBucketKey = false;
+
+	/** @var string[] Non-fatal `sse*` configuration issues found by parseEncryptionParams(), logged by logEncryptionWarnings() */
+	protected array $encryptionWarnings = [];
 }