What Is a Customer Master Key?

A Customer Master Key (CMK) is a Key Encryption Key (KEK) created by a user using KMS. It is used to encrypt and protect Data Encryption Keys (DEKs). One CMK can be used to encrypt one or multiple DEKs.

CMKs are categorized into custom keys and default keys.

Custom keys
Keys created or imported by users on the KMS console.

Default keys

When a user uses KMS for encryption in a cloud service for the first time, the cloud service automatically creates a key whose alias ends with /default.

On the KMS console, you can query Default Master Keys, but can neither disable them nor schedule their deletion.

**Table 1** Default Master Keys
Key Alias	Cloud Service
obs/default	Object Storage Service (OBS)
evs/default	Elastic Volume Service (EVS)
ims/default	Image Management Service (IMS)
sfs/default	Scalable File Service (SFS)