This topic introduces the basic concepts of encryption. Encryption can help you secure your data stored in Alibaba Cloud ECS and comply with security standards. You can protect the privacy, autonomy, and security of data and ensure the security of your business data without the need to build or maintain key management infrastructure. Both system disks and data disks can be encrypted.

Feature description

Alibaba Cloud ECS uses the industry-standard AES-256 algorithm to encrypt disks. Keys contain service keys and customer-created keys. You can obtain customer-created keys by using Bring Your Own Key (BYOK). Encryption and decryption have minimal impacts on ECS instance performance.

  • Data in the operating system of the ECS instance is automatically encrypted when you create an ECS instance from an encrypted system disk or image. The data is automatically decrypted when it is read. For more information about the procedure, see Encrypt a system disk.
  • The following types of data are automatically encrypted when you create an encrypted data disk and attach it to an ECS instance. The data is automatically decrypted when it is read. For more information about the procedure, see Encrypt a data disk.
    • Static data stored on an encrypted disk.
    • Data transmitted between an encrypted disk and an instance. Data in the operating system is not encrypted again.
    • Data transmitted from an instance to a backend storage cluster.
    • All snapshots created from an encrypted disk. These snapshots have the same encryption key as the disk.
    • All disks created from encrypted snapshots.

Keys

A customer master key (CMK) contains metadata such as the key ID, creation date, description, rotation plan, lifecycle status, and the key material that is used to encrypt and decrypt data. If you use a CMK to encrypt a disk, all subsequent data written to the disk is also encrypted with the same CMK. The CMK is also used to encrypt all snapshots and the disks that are created from these snapshots. The CMK is used only in the memory of the host where your ECS instance is running. The CMK is not stored on any storage media in plaintext. CMKs are stored in the key management infrastructure provided by Key Management Service (KMS). CMKs provide strong physical and logical security protection against unauthorized access. The key management infrastructure of Alibaba Cloud conforms to the recommendations in NIST SP 800-57 and uses cryptographic algorithms that comply with FIPS Publication 140-2.

The following table describes the types of CMKs that you can use to encrypt disks.
Type Description Source Scenario
Service key, the first key in the following figure When you activate KMS and use encryption for the first time within a region, KMS automatically creates a dedicated CMK for the ECS service within the region. The alias 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 when you want to enhance efficiency and convenience. For more information, see What is KMS?.
Customer-created key, the second key in the following figure The encryption keys that you create. You have full management permissions to create, rotate, and disable these keys, and define access control over them.
  • Source 1: The key that is created in KMS.
  • Source 2: The key that is created in KMS from key materials imported through BYOK.
You can use customer-created keys to improve operation flexibility and increase the number of keys.
Difference between a service key and a customer-created key

Billing

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

Feature or operation Billing
Encrypt system disks and data disks No
Use service keys that are provided by KMS No
CMKs that are created by you in KMS or created from key materials imported through BYOK. Yes
Read and write operations on disks, such as mounting (mount) and unmounting (umount) of disks, creation of partitions, and formatting of file systems No

Limits

  • You can encrypt data disks such as enhanced SSDs, standard SSDs, ultra disks, and basic disks.
  • You can encrypt system disks such as enhanced SSDs, standard SSDs, and ultra disks.
  • You cannot encrypt local disks.
  • You can encrypt system disks only when you are copying their custom images. You cannot perform the following operations on encrypted system disks:
    • Convert encrypted images to unencrypted images.
    • Copy encrypted images across regions.
    • Share encrypted images.
    • Export encrypted images.
  • You cannot directly convert unencrypted disks to encrypted disks.
  • You cannot directly convert encrypted disks to unencrypted disks.