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CREATE SYMMETRIC KEY (Transact-SQL)

  • Artikkeli

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics

Generates a symmetric key and specifies its properties in SQL Server.

This feature is incompatible with database export using Data Tier Application Framework (DACFx). You must drop all symmetric keys before exporting.

Transact-SQL syntax conventions

Note

This syntax is not supported by serverless SQL pool in Azure Synapse Analytics.

Syntax

CREATE SYMMETRIC KEY key_name
    [ AUTHORIZATION owner_name ]
    [ FROM PROVIDER provider_name ]
    WITH
        [
            <key_options> [ , ... n ]
            | ENCRYPTION BY <encrypting_mechanism> [ , ... n ]
        ]

<key_options> ::=
    KEY_SOURCE = 'pass_phrase'
    | ALGORITHM = <algorithm>
    | IDENTITY_VALUE = 'identity_phrase'
    | PROVIDER_KEY_NAME = 'key_name_in_provider'
    | CREATION_DISPOSITION = { CREATE_NEW | OPEN_EXISTING }

<algorithm> ::=
    DES | TRIPLE_DES | TRIPLE_DES_3KEY | RC2 | RC4 | RC4_128
    | DESX | AES_128 | AES_192 | AES_256

<encrypting_mechanism> ::=
    CERTIFICATE certificate_name
    | PASSWORD = 'password'
    | SYMMETRIC KEY symmetric_key_name
    | ASYMMETRIC KEY asym_key_name

Arguments

key_name

Specifies the unique name by which the symmetric key is known in the database. This is a required parameter. Temporary keys are designated when the key_name begins with one number (#) sign. For example, #temporaryKey900007. You can't create a symmetric key that has a name that starts with more than one #. You can't create a temporary symmetric key using an EKM provider.

AUTHORIZATION owner_name

Specifies the name of the database user or application role that owns this key.

FROM PROVIDER provider_name

Specifies an Extensible Key Management (EKM) provider and name. The key isn't exported from the EKM device. The provider must be defined first using the CREATE PROVIDER statement. For more information about creating external key providers, see Extensible Key Management (EKM).

Note

This option isn't available in a contained database.

KEY_SOURCE = 'pass_phrase'

Specifies a passphrase from which to derive the key.

IDENTITY_VALUE = 'identity_phrase'

Specifies an identity phrase from which to generate a GUID for tagging data that is encrypted with a temporary key.

PROVIDER_KEY_NAME = 'key_name_in_provider'

Specifies the name referenced in the Extensible Key Management provider.

Note

This option isn't available in a contained database.

CREATION_DISPOSITION = { CREATE_NEW | OPEN_EXISTING }

Creates or maps a symmetric key to an Extensible Key Management device.

  • CREATE_NEW

    Creates a new key on the Extensible Key Management device. If a key already exists on the device, the statement fails with an error.

  • OPEN_EXISTING

    Maps a SQL Server symmetric key to an existing Extensible Key Management key. If CREATION_DISPOSITION = OPEN_EXISTING isn't provided, this defaults to CREATE_NEW.

certificate_name

Specifies the name of the certificate that is used to encrypt the symmetric key. The certificate must already exist in the database.

'password'

Specifies a password from which to derive a TRIPLE_DES key with which to secure the symmetric key. password must meet the Windows password policy requirements of the computer that is running the instance of SQL Server. Always use strong passwords.

symmetric_key_name

Specifies a symmetric key, used to encrypt the key that is being created. The specified key must already exist in the database, and the key must be open.

asym_key_name

Specifies an asymmetric key, used to encrypt the key that is being created. This asymmetric key must already exist in the database.

<algorithm>

Specify the encrypting algorithm.

Warning

Beginning with SQL Server 2016 (13.x), all algorithms other than AES_128, AES_192, and AES_256 are deprecated. To use older algorithms (not recommended), you must set the database to database compatibility level 120 or lower.

Remarks

When a symmetric key is created, the symmetric key must be encrypted by using at least one of the following options:

  • certificate
  • password
  • symmetric key
  • asymmetric key
  • PROVIDER

The key can have more than one encryption of each type. In other words, a single symmetric key can be encrypted by using multiple certificates, passwords, symmetric keys, and asymmetric keys at the same time.

Caution

When a symmetric key is encrypted with a password instead of a certificate (or another key), the TRIPLE DES encryption algorithm is used to encrypt the password. Because of this, keys that are created with a strong encryption algorithm, such as AES, are themselves secured by a weaker algorithm.

The optional password can be used to encrypt the symmetric key before distributing the key to multiple users.

Temporary keys are owned by the user that creates them. Temporary keys are only valid for the current session.

IDENTITY_VALUE generates a GUID with which to tag data that is encrypted with the new symmetric key. This tagging can be used to match keys to encrypted data. The GUID generated by a specific phrase is always the same. After a phrase has been used to generate a GUID, the phrase can't be reused as long as there's at least one symmetric key in this database that is actively using the phrase. IDENTITY_VALUE is an optional clause; however, we recommend using it when you're storing data encrypted with a temporary key.

There's no default encryption algorithm.

Important

We don't recommend using the RC4 and RC4_128 stream ciphers to protect sensitive data. SQL Server doesn't further encode the encryption performed with such keys.

Information about symmetric keys is visible in the sys.symmetric_keys catalog view.

Symmetric keys can't be encrypted by symmetric keys created from the encryption provider.

Clarification regarding DES algorithms

  • DESX was incorrectly named. Symmetric keys created with ALGORITHM = DESX actually use the TRIPLE DES cipher with a 192-bit key. The DESX algorithm isn't provided. This feature will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.
  • Symmetric keys created with ALGORITHM = TRIPLE_DES_3KEY use TRIPLE DES with a 192-bit key.
  • Symmetric keys created with ALGORITHM = TRIPLE_DES use TRIPLE DES with a 128-bit key.

Deprecation of the RC4 algorithm

Repeated use of the same RC4 or RC4_128 KEY_GUID on different blocks of data, results in the same RC4 key because SQL Server doesn't provide a salt automatically. Using the same RC4 key repeatedly is a well known error that results in very weak encryption. Therefore we have deprecated the RC4 and RC4_128 keywords. This feature will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

Warning

The RC4 algorithm is only supported for backward compatibility. New material can only be encrypted using RC4 or RC4_128 when the database is in compatibility level 90 or 100. (Not recommended.) Use a newer algorithm such as one of the AES algorithms instead. In SQL Server material encrypted using RC4 or RC4_128 can be decrypted in any compatibility level.

Permissions

Requires ALTER ANY SYMMETRIC KEY permission on the database. If AUTHORIZATION is specified, requires IMPERSONATE permission on the database user or ALTER permission on the application role. If encryption is by certificate or asymmetric key, requires VIEW DEFINITION permission on the certificate or asymmetric key. Only Windows logins, SQL Server logins, and application roles can own symmetric keys. Groups and roles can't own symmetric keys.

Examples

A. Create a symmetric key

The following example creates a symmetric key called JanainaKey09 by using the AES 256 algorithm, and then encrypts the new key with certificate Shipping04.

CREATE SYMMETRIC KEY JanainaKey09
WITH ALGORITHM = AES_256
ENCRYPTION BY CERTIFICATE Shipping04;
GO

B. Create a temporary symmetric key

The following example creates a temporary symmetric key called #MarketingXXV from the passphrase: The square of the hypotenuse is equal to the sum of the squares of the sides. The key is provisioned with a GUID that is generated from the string Pythagoras and encrypted with certificate Marketing25.

CREATE SYMMETRIC KEY #MarketingXXV
WITH ALGORITHM = AES_128,
KEY_SOURCE
     = 'The square of the hypotenuse is equal to the sum of the squares of the sides',
IDENTITY_VALUE = 'Pythagoras'
ENCRYPTION BY CERTIFICATE Marketing25;
GO

C. Create a symmetric key using an Extensible Key Management (EKM) device

The following example creates a symmetric key called MySymKey by using a provider called MyEKMProvider and a key name of KeyForSensitiveData. It assigns authorization to User1 and assumes that the system administrator has already registered the provider called MyEKMProvider in SQL Server.

CREATE SYMMETRIC KEY MySymKey
AUTHORIZATION User1
FROM PROVIDER EKMProvider
WITH
PROVIDER_KEY_NAME='KeyForSensitiveData',
CREATION_DISPOSITION=OPEN_EXISTING;
GO

See also