CREATE COLUMN MASTER KEY (Transact-SQL)

APPLIES TO: yesSQL Server (starting with 2016) yesAzure SQL Database noAzure SQL Data Warehouse noParallel Data Warehouse

Creates a column master key metadata object in a database. A column master key metadata entry represents a key, stored in an external key store. The key protects (encrypts) column encryption keys when you're using the Always Encrypted (Database Engine) feature. Multiple column master keys allow for periodic key rotation to enhance security. Create a column master key in a key store and its related metadata object in the database by using the Object Explorer in SQL Server Management Studio or PowerShell. For details, see Overview of Key Management for Always Encrypted.

Topic link icon Transact-SQL Syntax Conventions

Important

Creating enclave-enabled keys (with ENCLAVE_COMPUTATIONS) requires Always Encrypted with secure enclaves.

Syntax

CREATE COLUMN MASTER KEY key_name   
    WITH (  
        KEY_STORE_PROVIDER_NAME = 'key_store_provider_name',  
        KEY_PATH = 'key_path'   
        [,ENCLAVE_COMPUTATIONS (SIGNATURE = signature)]
         )   
[;]  

Arguments

key_name
The name of the column master key in the database.

key_store_provider_name
Specifies the name of a key store provider. A key store provider is a client-side software component that holds a key store that has the column master key.

A client driver, enabled with Always Encrypted:

  • Uses a key store provider name
  • Searches for the key store provider in the driver's registry of key store providers

The driver then uses the provider to decrypt column encryption keys. The column encryption keys are protected by a column master key. The column master key is stored in the underlying key store. A plaintext value of the column encryption key is then used to encrypt query parameters that correspond to encrypted database columns. Or, the column encryption key decrypts query results from encrypted columns.

Always Encrypted-enabled client driver libraries include key store providers for popular key stores.

A set of available providers depends on the type and the version of the client driver. See the Always Encrypted documentation for particular drivers:

Develop Applications using Always Encrypted with the .NET Framework Provider for SQL Server

The following table shows the names of system providers:

Key store provider name Underlying key store
'MSSQL_CERTIFICATE_STORE' Windows Certificate Store
'MSSQL_CSP_PROVIDER' A store, such as a hardware security module (HSM), that supports Microsoft CryptoAPI.
'MSSQL_CNG_STORE' A store, such as a hardware security module (HSM), that supports Cryptography API: Next Generation.
'Azure_Key_Vault' See Getting Started with Azure Key Vault

In your Always Encrypted-enabled client driver, you can set up a custom key store provider that stores column master keys for which there's no built-in key store provider. The names of custom key store providers can't start with 'MSSQL_', which is a prefix reserved for Microsoft key store providers.

key_path
The path of the key in the column master key store. The key path must be valid for each client application expected to encrypt or decrypt data. The data is stored in a column that's (indirectly) protected by the referenced column master key. The client application must have access to the key. The format of the key path is specific to the key store provider. The following list describes the format of key paths for particular Microsoft system key store providers.

  • Provider name: MSSQL_CERTIFICATE_STORE

    Key path format: CertificateStoreName/CertificateStoreLocation/CertificateThumbprint

    Where:

    CertificateStoreLocation
    Certificate store location, which must be Current User or Local Machine. For more information, see Local Machine and Current User Certificate Stores.

    CertificateStore
    Certificate store name, for example 'My'.

    CertificateThumbprint
    Certificate thumbprint.

    Examples:

    N'CurrentUser/My/BBF037EC4A133ADCA89FFAEC16CA5BFA8878FB94'  
    
    N'LocalMachine/My/CA5BFA8878FB94BBF037EC4A133ADCA89FFAEC16'  
    
  • Provider name: MSSQL_CSP_PROVIDER

    Key path format: ProviderName/KeyIdentifier

    Where:

    ProviderName
    The name of a Cryptography Service Provider (CSP), which implements CAPI, for the column master key store. If you use an HSM as a key store, the provider name must be the name of the CSP your HSM vendor supplies. The provider must be installed on a client computer.

    KeyIdentifier
    Identifier of the key, used as a column master key, in the key store.

    Examples:

    N'My HSM CSP Provider/AlwaysEncryptedKey1'  
    
  • Provider name: MSSQL_CNG_STORE

    Key path format: ProviderName/KeyIdentifier

    Where:

    ProviderName
    Name of the Key Storage Provider (KSP), which implements the Cryptography: Next Generation (CNG) API, for the column master key store. If you use an HSM as a key store, the provider name must be the name of the KSP your HSM vendor supplies. The provider must be installed on a client computer.

    KeyIdentifier
    Identifier of the key, used as a column master key, in the key store.

    Examples:

    N'My HSM CNG Provider/AlwaysEncryptedKey1'  
    
  • Provider name: AZURE_KEY_STORE

    Key path format: KeyUrl

    Where:

    KeyUrl
    The URL of the key in Azure Key Vault

ENCLAVE_COMPUTATIONS
Specifies that the column master key is enclave-enabled. You can share all column encryption keys, encrypted with the column master key, with a server-side secure enclave and use them for computations inside the enclave. For more information, see Always Encrypted with secure enclaves.

signature
A binary literal that's a result of digitally signing key path and the ENCLAVE_COMPUTATIONS setting with the column master key. The signature reflects whether ENCLAVE_COMPUTATIONS is specified or not. The signature protects the signed values from being altered by unauthorized users. An Always Encrypted-enabled client driver verifies the signature and returns an error to the application if the signature is invalid. The signature must be generated using client-side tools. For more information, see Always Encrypted with secure enclaves.

Remarks

Create a column master key metadata entry before you create a column encryption key metadata entry in the database and before any column in the database can be encrypted using Always Encrypted. A column master key entry in the metadata doesn't contain the actual column master key. The column master key must be stored in an external column key store (outside of SQL Server). The key store provider name and the column master key path in the metadata must be valid for a client application. The client application needs to use the column master key to decrypt a column encryption key. The column encryption key is encrypted with the column master key. The client application also needs to query encrypted columns.

Permissions

Requires the ALTER ANY COLUMN MASTER KEY permission.

Examples

A. Creating a column master key

The following example creates a column master key metadata entry for a column master key. The column master key is stored in the Certificate Store for client applications that use the MSSQL_CERTIFICATE_STORE provider to access the column master key:

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
     KEY_STORE_PROVIDER_NAME = N'MSSQL_CERTIFICATE_STORE',   
     KEY_PATH = 'Current User/Personal/f2260f28d909d21c642a3d8e0b45a830e79a1420'  
   );  

Create a column master key metadata entry for a column master key. Client applications, which use the MSSQL_CNG_STORE provider, access the column master key:

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
    KEY_STORE_PROVIDER_NAME = N'MSSQL_CNG_STORE',    
    KEY_PATH = N'My HSM CNG Provider/AlwaysEncryptedKey'  
);  

Create a column master key metadata entry for a column master key. The column master key is stored in the Azure Key Vault, for client applications that use the AZURE_KEY_VAULT provider, to access the column master key.

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
    KEY_STORE_PROVIDER_NAME = N'AZURE_KEY_VAULT',  
    KEY_PATH = N'https://myvault.vault.azure.net:443/keys/  
        MyCMK/4c05f1a41b12488f9cba2ea964b6a700');  

Create a column master key metadata entry for a column master key. The column master key is stored in a custom column master key store:

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
    KEY_STORE_PROVIDER_NAME = 'CUSTOM_KEY_STORE',    
    KEY_PATH = 'https://contoso.vault/sales_db_tce_key'  
);  

B. Creating an enclave-enabled column master key

The following example creates a column master key metadata entry for an enclave-enabled column master key. The enclave-enabled column master key is stored in a Certificate Store, for client applications that use the MSSQL_CERTIFICATE_STORE provider to access the column master key:

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
     KEY_STORE_PROVIDER_NAME = N'MSSQL_CERTIFICATE_STORE',   
     KEY_PATH = 'Current User/Personal/f2260f28d909d21c642a3d8e0b45a830e79a1420'  
     ENCLAVE_COMPUTATIONS (SIGNATURE = 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
  );  

Create a column master key metadata entry for an enclave-enabled column master key. The enclave-enabled column master key is stored in the Azure Key Vault, for client applications that use the AZURE_KEY_VAULT provider, to access the column master key.

CREATE COLUMN MASTER KEY MyCMK  
WITH (  
    KEY_STORE_PROVIDER_NAME = N'AZURE_KEY_VAULT',  
    KEY_PATH = N'https://myvault.vault.azure.net:443/keys/MyCMK/4c05f1a41b12488f9cba2ea964b6a700');
    ENCLAVE_COMPUTATIONS (SIGNATURE = 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
  );

See Also