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ALTER MASTER KEY (Transact-SQL)

Changes the properties of a database master key.

Applies to: SQL Server (SQL Server 2008 through current version).

Topic link icon Transact-SQL Syntax Conventions

ALTER MASTER KEY <alter_option>

<alter_option> ::=
    <regenerate_option> | <encryption_option>

<regenerate_option> ::=
    [ FORCE ] REGENERATE WITH ENCRYPTION BY PASSWORD = 'password'

<encryption_option> ::=
    ADD ENCRYPTION BY { SERVICE MASTER KEY | PASSWORD = 'password' }
    | 
    DROP ENCRYPTION BY { SERVICE MASTER KEY | PASSWORD = 'password' }

PASSWORD ='password'

Specifies a password with which to encrypt or decrypt the database master key. password must meet the Windows password policy requirements of the computer that is running the instance of SQL Server.

The REGENERATE option re-creates the database master key and all the keys it protects. The keys are first decrypted with the old master key, and then encrypted with the new master key. This resource-intensive operation should be scheduled during a period of low demand, unless the master key has been compromised.

SQL Server 2012 uses the AES encryption algorithm to protect the service master key (SMK) and the database master key (DMK). AES is a newer encryption algorithm than 3DES used in earlier versions. After upgrading an instance of the Database Engine to SQL Server 2012 the SMK and DMK should be regenerated in order to upgrade the master keys to AES. For more information about regenerating the SMK, see ALTER SERVICE MASTER KEY (Transact-SQL).

When the FORCE option is used, key regeneration will continue even if the master key is unavailable or the server cannot decrypt all the encrypted private keys. If the master key cannot be opened, use the RESTORE MASTER KEY statement to restore the master key from a backup. Use the FORCE option only if the master key is irretrievable or if decryption fails. Information that is encrypted only by an irretrievable key will be lost.

The DROP ENCRYPTION BY SERVICE MASTER KEY option removes the encryption of the database master key by the service master key.

ADD ENCRYPTION BY SERVICE MASTER KEY causes a copy of the master key to be encrypted using the service master key and stored in both the current database and in master.

Requires CONTROL permission on the database. If the database master key has been encrypted with a password, knowledge of that password is also required.

The following example creates a new database master key for AdventureWorks and reencrypts the keys below it in the encryption hierarchy.

USE AdventureWorks2012;
ALTER MASTER KEY REGENERATE WITH ENCRYPTION BY PASSWORD = 'dsjdkflJ435907NnmM#sX003';
GO

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