This topic describes the basic concepts of encryption. In the scenarios that require data security and regulatory compliance, you can encrypt your data stored in Alibaba Cloud Elastic Compute Service (ECS). You can implement disk encryption to protect the privacy, autonomy, and security of data without the need to establish or maintain key management infrastructure. Both system disks and data disks can be encrypted.

Description

ECS uses the industry-standard AES-256 algorithm to encrypt disks with keys. Encryption keys can be the service keys provided by Key Management Service (KMS) or your own keys created by using the Bring Your Own Key (BYOK) feature. Encryption and decryption have minimal impacts on ECS instance performance. The performance of disks for which encryption is disabled is higher than that of disks for which encryption is enabled. The amount that performance degrades varies based on the upper-layer applications on disks for which encryption is enabled.

  • When you create an ECS instance by using an encrypted system disk or image, data in the operating system of the ECS instance is automatically encrypted. The data is automatically decrypted when it is read. For more information how to create an encrypted system disk, see Encrypt a system disk.
  • The following types of data are encrypted when you create an encrypted disk and attach it to an ECS instance. The data is decrypted when it is read. For more information about how to create an encrypted data disk, see Encrypt a data disk.
    • Data at rest that is stored on the encrypted disk.
    • Data transmitted between the encrypted disk and the ECS instance, excluding data in the operating system.
    • Data transmitted from the ECS instance to a backend storage cluster.
    • All snapshots created from the encrypted disk. These snapshots have the same encryption key as the disk.
    • All disks created from the encrypted snapshots.

Encryption keys

By default, the disk encryption feature uses a service key to encrypt your data. You can also create a custom key to encrypt your data. Each disk is provided with a customer master key (CMK) and a data key (DK) by KMS and uses the envelope encryption mechanism to encrypt your data. In the envelope encryption mechanism, CMKs are placed under strong logical and physical security protection by the key management infrastructure provided by KMS. An Alibaba Cloud service must be authorized to use a CMK to generate a DK to encrypt business data or decrypt the ciphertext of the DK to decrypt business data. The plaintext of the DK is only used in the memory of the host where your ECS instance resides. The DK is not stored in plaintext in persistent storage medium.

The following table describes the types of CMKs that you can use to encrypt disks.
Type Description Source Scenario
Service key, key ① in the following figure The dedicated CMK that is automatically created by KMS for ECS in a region when you activate KMS and use encryption for the first time within the region. The alias name of the CMK is acs/ecs. Service keys cannot be deleted or disabled. The default service CMK provided by KMS. You can use service keys to encrypt disks in a more efficient and convenient manner. For more information, see What is Key Management Service?.
Customer-created key, key ② in the following figure The encryption keys that you create. You have full permissions to create, rotate, and disable these keys, and define access control over them.
  • Source 1: A key that is created in KMS.
  • Source 2: A key created in KMS from key materials imported by using the BYOK feature
You can use customer-created keys to encrypt disks in a more flexible manner and increase the number of keys.
Differences between a service key and a customer-created key

Billing

The following table describes the billing information of features and operations related to encryption. Make sure that your account balance is sufficient. Otherwise, operations that incur costs may fail.

Operation Billable
Encrypt system disks and data disks. No
Use service keys that are provided by KMS. No
Create CMKs in KMS or from key materials imported by using the BYOK feature. Yes
Perform read and write operations on disks, such as mounting (mount) and unmounting (umount) partitions, creating partitions, and formatting file systems. No

Limits

  • Data disks of the following categories support encryption: enhanced SSDs (ESSDs), standard SSDs, ultra disks, and basic disks.
  • System disks of the following categories support encryption: ESSDs, standard SSDs, and ultra disks.
  • Local disks do not support encryption.
  • System disks can be encrypted only when custom images are copied. The following operations cannot be performed on encrypted system disks:
    • Convert encrypted images to unencrypted images.
    • Copy encrypted images across regions.
    • Share encrypted images.
    • Export encrypted images.
  • Unencrypted disks cannot be directly converted to encrypted disks.
  • Encrypted disks cannot be directly converted to unencrypted disks.