EVS Encryption

What Is EVS Encryption?

In case your services require encryption for the data stored on EVS disks, EVS provides you with the encryption function. You can encrypt newly created EVS disks. Keys used by encrypted EVS disks are provided by the Key Management Service (KMS), which is secure and convenient. Therefore, you do not need to establish and maintain the key management infrastructure.

Keys Used for EVS Encryption

The keys provided by KMS include a Default Master Key and Customer Master Keys (CMKs).

Default Master Key: A key that is automatically created by EVS through KMS and named evs/default.
The Default Master Key cannot be disabled and does not support scheduled deletion.
CMKs: Keys created by users. You may use existing CMKs or create new CMKs to encrypt disks. For details, see Management > Creating a CMK in the Key Management Service User Guide.

If disks are encrypted using CMKs and a CMK is then disabled or scheduled for deletion, the disks encrypted by this CMK can no longer be read from or written to and data on these disks may never be restored. See Table 1 for more information.

**Table 1** Impact of CMK unavailability
CMK Status	Impact	How to Restore
Disabled	For an encrypted disk already attached: The disk will become inaccessible after a period of time, or the disk data can never be restored. If the disk is detached later, it can never be attached again. For an encrypted disk not attached: The disk cannot be attached anymore.	Enable the CMK. For details, see Managing CMKs > Enabling One or More CMKs in the Key Management Service User Guide.
Scheduled deletion		Cancel the scheduled deletion for the CMK. For details, see Managing CMKs > Canceling the Scheduled Deletion of One or More CMKs in the Key Management Service User Guide.
Deleted		Data on the disks can never be restored.

Relationships Between Encrypted Disks, Backups and Snapshots

The encryption function can be used to encrypt system disks, data disks, backups and snapshots. The details are as follows:

System disk encryption relies on the image that is used to create the server.
- If an encrypted image is used to create the server, the system disk will be encrypted by default, and the system disk and image share the same encryption method. For details, see Managing Private Images > Encrypting Images in the Image Management Service User Guide.
- If a non-encrypted image is used to create the server, you can determine whether to encrypt the system disk during the server creation. For details, see Getting Started > Creating an ECS > Step 1: Configure Basic Settings in the Elastic Cloud Server User Guide.
If an empty disk is created, you can determine whether to encrypt the disk or not. The encryption attribute of the disk cannot be changed after the disk has been created.
If a disk is created from a snapshot, the encryption attribute of the disk will be the same as that of the snapshot's source disk.
If a disk is created from a backup, the encryption attribute of the disk does not need to be the same as that of the backup.
If a snapshot is created for a disk, the encryption attribute of the snapshot is the same as that of the disk.

Who Can Use the Encryption Function?

The security administrator (having Security Administrator permissions) can grant the KMS access rights to EVS for using the encryption function.
When a user who does not have the Security Administrator permissions needs to use the encryption function, the condition varies depending on whether the user is the first one ever in the current region or project to use this function.
- If the user is the first one ever in the current region or project to use this function, the user must contact a user having the Security Administrator permissions to grant the KMS access rights to EVS. Then, the user can use encryption.
- If the user is not the first one ever in the current region or project to use this function, the user can use encryption directly.

From the perspective of a tenant, as long as the KMS access rights have been granted to EVS in a region, all the users in the same region can directly use the encryption function.

If there are multiple projects in the current region, the KMS access rights need to be granted to each project in this region.

Application Scenarios of EVS Encryption

Figure 1 shows the user relationships under regions and projects from the perspective of a tenant. The following example uses region B to describe the two scenarios of using the encryption function.

Figure 1 User relationships
Click to enlarge

If the security administrator uses the encryption function for the first time ever, the operation process is as follows:
1. Grant the KMS access rights to EVS.
  After the KMS access rights have been granted, the system automatically creates a Default Master Key and names it evs/default. DMK can be used to encrypt EVS disks.
  
  EVS encryption relies on KMS. When the encryption function is used for the first time ever, the KMS access rights need to be granted to EVS. After the KMS access rights have been granted, all users in this region can use the encryption function, without requiring the KMS access rights to be granted again.
2. Select a key.
  You can select one of the following keys:
  - DMK: evs/default
  - CMKs: Existing or newly created CMKs. For details, see Creating a CMK in the Key Management Service User Guide.
After the security administrator has used the encryption function, all users in Region B can directly use encryption.
If User E (common user) uses the encryption function for the first time ever, the operation process is as follows:
1. When user E uses encryption, and the system prompts a message indicating that the KMS access rights have not been granted to EVS.
2. Contact the security administrator to grant the KMS access rights to EVS.
After the KMS access rights have been granted to EVS, User E as well as all users in Region B can directly use the encryption function and do not need to contact the security administrator to grant the KMS access rights to EVS again.