A Customer Master Key (CMK) is a Key Encryption Key (KEK) created by a user on KMS. It is used to encrypt and protect DEKs. One CMK can be used to encrypt one or more 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 with the alias suffix /default.

You can use the management console to query but cannot disable or schedule the deletion of Default Master Keys.

**Table 1** Default Master Keys
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)

What Is a Customer Master Key?