cloud: update Dual-Layer Data Encryption for Premium

TOC-tidb-cloud-premium.md

@@ -240,6 +240,7 @@
     - [Configure Firewall Rules for Public Endpoints](/tidb-cloud/configure-serverless-firewall-rules-for-public-endpoints.md)
     - [TLS Connections to TiDB Cloud](/tidb-cloud/premium/tidb-cloud-tls-connect-to-premium.md)
   - Data Access Control
+    - [Dual-Layer Data Encryption](/tidb-cloud/premium/dual-layer-data-encryption-premium.md)
     - [User-Controlled Log Redaction](/tidb-cloud/tidb-cloud-log-redaction.md)
   - Audit Management
     - [Database Audit Logging](/tidb-cloud/premium/tidb-cloud-auditing-premium.md)

tidb-cloud/manage-projects-and-resources.md

@@ -97,6 +97,11 @@ To create a new project, take the following steps:
 3. Depending on which type of TiDB Cloud resources you are creating the project for, do one of the following:
 
     - If the project is created for TiDB X instances, click **Confirm**.
+
+        > **Note:**
+        >
+        > For {{{ .premium }}} instances, encryption is configured per instance rather than per project. After you create the instance, you can enable [Dual-Layer Data Encryption](/tidb-cloud/premium/dual-layer-data-encryption-premium.md) to add a database-layer encryption on top of the default storage-layer encryption.
+
     - If the project is created for {{{ .dedicated }}} clusters, select the **Create for Dedicated Cluster** option, configure [Customer-Managed Encryption Keys (CMEK)](/tidb-cloud/tidb-cloud-encrypt-cmek-aws.md) and [maintenance window](/tidb-cloud/configure-maintenance-window.md) for the project, and then click **Confirm**.
 
 ### Manage a project

tidb-cloud/premium/dual-layer-data-encryption-premium.md

@@ -0,0 +1,163 @@
+---
+title: Dual-Layer Data Encryption
+summary: Learn how to enable and manage Dual-Layer Data Encryption for your {{{ .premium }}} instance hosted on AWS.
+---
+
+# Dual-Layer Data Encryption
+
+This document describes how to enable and manage Dual-Layer Data Encryption for your {{{ .premium }}} instance hosted on AWS.
+
+> **Note:**
+>
+> Currently, the Dual-Layer Data Encryption feature is only available upon request. To request this feature, click **?** in the lower-right corner of the [TiDB Cloud console](https://tidbcloud.com), and then click **Support Tickets** to go to the [Help Center](https://tidb.support.pingcap.com/servicedesk/customer/portals). Create a ticket, fill in "Apply for Dual-Layer Data Encryption" in the **Description** field, and then click **Submit**.
+
+## Overview
+
+By default, {{{ .premium }}} encrypts data at rest on instance storage and snapshot volumes, providing a baseline level of data security. In addition, {{{ .premium }}} supports combining TiDB storage engine encryption with your cloud provider's Key Management Service (KMS). This additional layer is called **Dual-Layer Data Encryption**.
+
+### Encryption mechanism
+
+To provide a higher level of data security, {{{ .premium }}} uses a two-layer architecture for data-at-rest encryption. Both storage-layer and database-layer encryption protect your data.
+
+- **Storage-layer encryption**
+
+    - The underlying cloud service provider provides storage-layer encryption on its storage infrastructure. For example, on AWS, this includes Amazon Elastic Block Store (EBS) volume encryption and Amazon Simple Storage Service (S3) bucket encryption.
+    - This layer is enabled by default for all {{{ .premium }}} instances and cannot be disabled. It provides the foundational security baseline for data at rest.
+
+- **Database-layer encryption**
+
+    - In addition to storage-layer encryption, {{{ .premium }}} supports an optional database-layer encryption feature (labeled **Dual-Layer Data Encryption** in the TiDB Cloud console). When you enable it, the feature encrypts data stored in TiKV, changefeed data, and backup data.
+    - This mechanism keeps data encrypted within the database system, which reduces the risk of data leakage during internal processing and data movement.
+    - Unlike storage-layer encryption, database-layer encryption is user-configurable. You can choose either a Customer-Managed Encryption Key (CMEK) or a Service-Managed Encryption Key, depending on your security compliance and operational requirements.
+
+### Backup and restore considerations
+
+When you enable Dual-Layer Data Encryption, the backup data for your {{{ .premium }}} instance is also encrypted. Any new instance restored from this backup inherits the encryption attributes and KMS master key of the original instance.
+
+Because backup data requires the original KMS master key for access, make sure that you meet the following requirements:
+
+- **Maintain key availability**: even if you delete the original {{{ .premium }}} instance, keep the associated KMS master key active so that you can recover the backup data.
+- **Ensure correct authorization**: during a restore operation, configure the exact same KMS master key that is associated with the backup, and make sure that the key has the required permissions for data access.
+
+### Key management options
+
+Dual-Layer Data Encryption uses AWS KMS to manage master keys for data-at-rest encryption. You can choose between two key management options:
+
+- **Customer-Managed Encryption Key (CMEK)**
+
+    You create, own, and manage your AWS KMS master key. This option provides full control over encryption and is suitable for organizations with strict security requirements.
+
+    > **Warning:**
+    >
+    > You are fully responsible for maintaining the key's security and availability. If you delete the configured CMEK, your {{{ .premium }}} instance becomes unusable, and you cannot recover the encrypted data.
+
+- **Service-Managed Encryption Key**
+
+    {{{ .premium }}} automatically creates and manages the KMS master key on your behalf. This option offers a balance of security and convenience with no maintenance overhead.
+
+    - The key is a symmetric encryption key.
+    - The key is generated automatically when you create your first encrypted {{{ .premium }}} instance in a given region.
+    - A single key is created per organization per region and is shared across all {{{ .premium }}} instances in that region.
+    - The key is automatically deleted only after all data encrypted with it has been removed from your organization.
+
+## Limitations
+
+- This feature currently supports only AWS KMS. Support for Alibaba Cloud KMS is planned for a future release.
+- Data encryption applies to data stored by TiKV, changefeed data, and backup data. Support for TiFlash data encryption is planned for a future release.
+- After you enable Dual-Layer Data Encryption, you cannot modify the encryption configuration of the {{{ .premium }}} instance.
+- Custom encryption algorithms are not supported. You can rotate only the KMS master key. Rotating other encryption keys is not supported.
+- Your AWS KMS key must be in the same region as your {{{ .premium }}} instance. As a result, cross-region restore operations are not supported for backups that use a CMEK.
+
+## Enable Dual-Layer Data Encryption
+
+You can enable Dual-Layer Data Encryption either when you create a {{{ .premium }}} instance or after instance creation.
+
+### Enable encryption during instance creation
+
+When you create a {{{ .premium }}} instance, you can enable Dual-Layer Data Encryption. Depending on your security and operational requirements, choose either a **Customer-Managed Encryption Key (CMEK)** or a **Service-Managed Encryption Key**.
+
+#### Option 1: Customer-Managed Encryption Key (CMEK)
+
+To use your own encryption key, take the following steps:
+
+1. Create a symmetric encryption key in AWS KMS.
+
+    The key must be in the **same region** as the planned {{{ .premium }}} instance. For detailed instructions, see [Create a symmetric encryption KMS key](https://docs.aws.amazon.com/kms/latest/developerguide/create-symmetric-cmk.html).
+
+2. Configure the CMEK in the [TiDB Cloud console](https://tidbcloud.com):
+
+    1. On the [**My TiDB**](https://tidbcloud.com/tidbs) page, click **Create Resource**.
+    2. Select the {{{ .premium }}} plan and complete the basic configuration.
+    3. In the **Dual-Layer Data Encryption** section, click **Enable**.
+    4. Select **Customer-Managed Encryption Key (CMEK)**, and then click **Add KMS Key ARN**.
+    5. Copy the displayed JSON policy and save it as `ROLE-TRUST-POLICY.JSON`. This file defines the required trust relationship.
+    6. In the AWS KMS console, add this trust policy to your key. For more information, see [Key policies in AWS KMS](https://docs.aws.amazon.com/kms/latest/developerguide/key-policies.html).
+    7. Return to the TiDB Cloud console, scroll to the bottom of the key creation page, and enter the **KMS Key ARN** that you obtained from AWS KMS.
+    8. To verify the trust relationship, click **Test and Add KMS Key ARN**.
+    9. After the verification succeeds, click **Create** to finish creating your {{{ .premium }}} instance.
+
+#### Option 2: Service-Managed Encryption Key
+
+To let TiDB Cloud manage the encryption key on your behalf, take the following steps:
+
+1. On the [**My TiDB**](https://tidbcloud.com/tidbs) page, click **Create Resource**.
+2. Select the {{{ .premium }}} plan and complete the basic configuration.
+3. In the **Dual-Layer Data Encryption** section, click **Enable**.
+4. Select **Service-Managed Encryption Key**.
+5. Click **Create** to finish creating your {{{ .premium }}} instance.
+
+### Enable encryption for an existing instance
+
+If you do not enable encryption when creating an instance, you can enable it later. Depending on your requirements, choose either a Customer-Managed Encryption Key (CMEK) or a Service-Managed Encryption Key.
+
+> **Note:**
+>
+> Enabling encryption on an existing instance might take some time to complete.
+
+#### Option 1: Customer-Managed Encryption Key (CMEK)
+
+Before you begin, make sure that you have created a symmetric encryption key in AWS KMS. Then, take the following steps:
+
+1. On the **Security** page of your {{{ .premium }}} instance, click **Enable** in the **Dual-Layer Data Encryption** section.
+2. Select **Customer-Managed Encryption Key (CMEK)**, and then click **Add KMS Key ARN**.
+3. Copy the displayed JSON policy and save it as `ROLE-TRUST-POLICY.JSON`. This file defines the required trust relationship.
+4. In the AWS KMS console, add this trust policy to your key. For more information, see [Key policies in AWS KMS](https://docs.aws.amazon.com/kms/latest/developerguide/key-policies.html).
+5. Return to the TiDB Cloud console, scroll to the bottom of the page, and enter the **KMS Key ARN** that you obtained from AWS KMS.
+6. To verify the trust relationship, click **Test and Add KMS Key ARN**.
+7. To enable Dual-Layer Data Encryption, click **Enable**.
+
+#### Option 2: Service-Managed Encryption Key
+
+To let TiDB Cloud manage the encryption key on your behalf, take the following steps:
+
+1. On the **Security** page of your {{{ .premium }}} instance, click **Enable** in the **Dual-Layer Data Encryption** section.
+2. Select **Service-Managed Encryption Key**.
+3. Click **Enable**.
+
+## View encryption status
+
+After you enable encryption, check the status in the following places:
+
+- On the **Overview** page of your {{{ .premium }}} instance, the **Encryption** field shows the active key management method: either **Enabled with Customer-Managed Encryption Key (CMEK)** or **Enabled with Service-Managed Encryption Key**.
+- On the **Security** page, you can view detailed configuration of Dual-Layer Data Encryption.
+
+## Restore from an encrypted backup
+
+Backups created from an encrypted {{{ .premium }}} instance are also encrypted. When you restore an encrypted backup, the new instance must use consistent encryption settings.
+
+### Restore a backup encrypted with a CMEK
+
+If the backup is encrypted with a CMEK, make sure that the new instance can access the KMS master key during the restore. The key ARN remains unchanged.
+
+To verify access, click **Check** to start the trust policy verification. TiDB Cloud then checks whether the authorized TiDB Cloud account in the key policy matches the account that is associated with the original backup:
+
+- If the accounts match, no further authorization is required.
+- If the accounts do not match, copy the provided key policy and update it in AWS KMS. This update re-authorizes the key and ensures that the new instance can access it.
+
+### Restore a backup encrypted with a Service-Managed Encryption Key
+
+If the backup is encrypted with a Service-Managed Encryption Key, the restored instance automatically inherits the same key type. During restore, encryption is enabled by default, and the key type is set to **Service-Managed Encryption Key**.
+
+## Rotate a Customer-Managed Encryption Key (CMEK)
+
+To rotate a CMEK, you can [enable automatic key rotation](https://docs.aws.amazon.com/kms/latest/developerguide/rotating-keys-enable.html) in AWS KMS. No additional TiDB Cloud configuration is required.