Rotate the Transparent Data Encryption (TDE) protector

APPLIES TO: Azure SQL Database Azure Synapse Analytics

This article describes key rotation for a server using a TDE protector from Azure Key Vault. Rotating the logical TDE Protector for a server means switching to a new asymmetric key that protects the databases on the server. Key rotation is an online operation and should only take a few seconds to complete, because this only decrypts and re-encrypts the database's data encryption key, not the entire database.

Important considerations when rotating the TDE Protector

  • When the TDE protector is changed/rotated, old backups of the database, including backed-up log files, are not updated to use the latest TDE protector. To restore a backup encrypted with a TDE protector from Key Vault, make sure that the key material is available to the target server. Therefore, we recommend that you keep all the old versions of the TDE protector in Azure Key Vault (AKV), so database backups can be restored.
  • Even when switching from customer managed key (CMK) to service-managed key, keep all previously used keys in AKV. This ensures database backups, including backed-up log files, can be restored with the TDE protectors stored in AKV.
  • Apart from old backups, transaction log files might also require access to the older TDE Protector. To determine if there are any remaining logs that still require the older key, after performing key rotation, use the sys.dm_db_log_info dynamic management view (DMV). This DMV returns information on the virtual log file (VLF) of the transantion log along with its encryption key thumbprint of the VLF.
  • Older keys need to be kept in AKV and available to the server based on the backup retention period configured as back of backup retention policies on the database. This helps ensure any Long Term Retention (LTR) backups on the server can still be restored using the older keys.

Note

A paused dedicated SQL pool in Azure Synapse Analytics must be resumed before key rotations.

Important

Do not delete previous versions of the key after a rollover. When keys are rolled over, some data is still encrypted with the previous keys, such as older database backups, backed-up log files and transaction log files.

Note

This article applies to Azure SQL Database, Azure SQL Managed Instance, and Azure Synapse Analytics (dedicated SQL pools (formerly SQL DW)). For documentation on Transparent Data Encryption for dedicated SQL pools inside Synapse workspaces, see Azure Synapse Analytics encryption.

Prerequisites

For Az module installation instructions, see Install Azure PowerShell. For specific cmdlets, see AzureRM.Sql.

Important

The PowerShell Azure Resource Manager (RM) module is still supported, but all future development is for the Az.Sql module. The AzureRM module will continue to receive bug fixes until at least December 2020. The arguments for the commands in the Az module and in the AzureRm modules are substantially identical. For more about their compatibility, see Introducing the new Azure PowerShell Az module.

Manual key rotation

Manual key rotation uses the following commands to add a completely new key, which could be under a new key name or even another key vault. Using this approach supports adding the same key to different key vaults to support high-availability and geo-dr scenarios.

Note

The combined length for the key vault name and key name cannot exceed 94 characters.

Use the Add-AzKeyVaultKey, Add-AzSqlServerKeyVaultKey, and Set-AzSqlServerTransparentDataEncryptionProtector cmdlets.

# add a new key to Key Vault
Add-AzKeyVaultKey -VaultName <keyVaultName> -Name <keyVaultKeyName> -Destination <hardwareOrSoftware>

# add the new key from Key Vault to the server
Add-AzSqlServerKeyVaultKey -KeyId <keyVaultKeyId> -ServerName <logicalServerName> -ResourceGroup <SQLDatabaseResourceGroupName>
  
# set the key as the TDE protector for all resources under the server
Set-AzSqlServerTransparentDataEncryptionProtector -Type AzureKeyVault -KeyId <keyVaultKeyId> `
   -ServerName <logicalServerName> -ResourceGroup <SQLDatabaseResourceGroupName>

Switch TDE protector mode

  • To switch the TDE protector from Microsoft-managed to BYOK mode, use the Set-AzSqlServerTransparentDataEncryptionProtector cmdlet.

    Set-AzSqlServerTransparentDataEncryptionProtector -Type AzureKeyVault `
         -KeyId <keyVaultKeyId> -ServerName <logicalServerName> -ResourceGroup <SQLDatabaseResourceGroupName>
    
  • To switch the TDE protector from BYOK mode to Microsoft-managed, use the Set-AzSqlServerTransparentDataEncryptionProtector cmdlet.

    Set-AzSqlServerTransparentDataEncryptionProtector -Type ServiceManaged `
         -ServerName <logicalServerName> -ResourceGroup <SQLDatabaseResourceGroupName>
    

Next steps