Always encrypted database

Question

We need to configure Always Encrypted feature for all databases. We wanted to create common Column Master Key in Master database so that we can link CMK to all databases on server. But we are not able to link CMK created in master DB to all databases. We need to create individually create master key in each database. Is there any way to create a CMK in master database and refer to all databases on the server.

Answer 1

Column Master Key is per-database object, i.e. you can't share it between databases. However, it is nothing more than metadata, i.e. a pointer where the actual key (certificate) is stored. With Always Encrypted the database do not have access to the actual encryption keys. They are stored in external key store (Windows Certificate Store, Azure Key Vault). So what you need to do is to replicate (copy) the existing certificate by registering it in the rest of the databases. Just script the existing CMK as CREATE COLUMN MASTER KEY statement and execute it in each of the databases:

CREATE COLUMN MASTER KEY [CMK_Auto1]
WITH
(
    KEY_STORE_PROVIDER_NAME = N'MSSQL_CERTIFICATE_STORE',
    KEY_PATH = N'CurrentUser/my/2CC027B4FCA85D4244B528E8CA5F73D1EBB18C69'
)
GO

This will create a new CMK in each database, but all of them will use the same certificate to encrypt the data. Then encrypt the columns you want using the existing CMK, which you created with the script above.