Migrating or Recovering a TDE Protected Database 

When encrypting a database with Transparent Data Encryption (TDE), a vital consideration is to make sure we are prepared for the scenario where something goes wrong. For instance, if the server hosting our SQL instance goes belly-up, can we recover the data that we have encrypted with TDE?

In the ordinary recovery scenario, we would make sure that we have appropriate backups of our database, and that they (or copies of them) are stored off the server itself so that we can access them in case of a failure.

If you have followed the instructions in the previous posts, then you will also have taken a backup of the certificate and private key via the following command:

BACKUP CERTIFICATE MyTDECert  
TO FILE = 'C:\Test\MyTDECert.cer' 
WITH PRIVATE KEY  

    FILE = 'C:\Test\MyTDECert_PrivateKeyFile.pvk', 
    ENCRYPTION BY PASSWORD = 'UseAStrongPasswordHereToo!£$7' 
);

You need to make sure that these are also stored securely off the server and that you have kept the password you used somewhere you can access it – but not so accessible that unauthorized users can read it.

In summary you need:

  • The database backup file
  • The backup of the certificate
  • The backup of the private key
  • The password used to encrypt the private key

Armed with those objects, you are equipped to restore your database to another SQL Instance. Working on the new SQL instance, the steps are straightforward.

Create a Database Master Key (DMK) if One Doesn’t Exist

The new SQL instance will need a DMK if one doesn’t already exist. You can create one with the following code:

USE master;
CREATE MASTER KEY
ENCRYPTION BY PASSWORD = 'UseAStrongPasswordHere!£$7';

Note that this will be a new and unique DMK, it will not be the same as the one you had on your old instance – and you don’t need to use the same password to protect it.

Restore the Certificate and Private Key

On the new SQL instance, you need to restore the certificate and private key into the master database with the following SQL:

USE master;
CREATE CERTIFICATE MyTDECert
FROM FILE = ‘C:\Test\MyTDECert.cer’
WITH PRIVATE KEY
(
   FILE = ‘C:\Test\MyTDECert_PrivateKeyFile.pvk’,
   DECRYPTION BY PASSWORD = ‘UseAStrongPasswordHereToo!£$7’
);

This will decrypt your key using the password supplied, and then re-encrypt it using the DMK you created. Then the certificate and its key will be stored in the master database on your new SQL instance.

If you’ve done something wrong, it’s entirely possible you may get an error at this stage, commonly:
Msg 15208, Level 16, State 6, Line 56
The certificate, asymmetric key, or private key file is not valid or does not exist; or you do not have permissions for it.

If you’re confident that all details specified are correct, and that the certificate and private key were backed up properly, then the most likely issue is that the current SQL instance doesn’t have access to the file path you’ve placed the files in.

Another possible issue is that you receive an error telling you the certificate already exists. If you have checked and verified that a certificate with the same name doesn’t exist, then the most probable cause is that you have another certificate with the same thumbprint. The thumbprint is the actual identifier for the certificate (the name we give it is more of a friendly name).

Restore the Database

Once you’ve completed the previous steps you are ready to restore the database from the backup. You do that as you would restore any other database. Potentially as simply as with the following command:

RESTORE DATABASE TestTDE FROM DISK = 'C:\Test\TestTDE.bak';

Then you’ll find you can access your database and view data without any issues. At this point you can celebrate – you are done. You only get a problem if you haven’t set up the certificate and key correctly, or you have the wrong one, in which case you get an error like the following:

Msg 33111, Level 16, State 3, Line 2
Cannot find server certificate with thumbprint ‘0x682C8797633B9AD8875967502861CCAE33ECAD66’.
Msg 3013, Level 16, State 1, Line 2
RESTORE DATABASE is terminating abnormally.

In the next post we’ll look at one case where you “may” be able to recover your TDE database if you’re in the unfortunate position of not having the certificate and private key from the old SQL Server instance.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

Things to look out for while TDE is encrypting existing data

Monitoring for Problems

The encryption of your existing data occurs as a background process referred to as the encryption scan, but it will consume resources while it runs, so if you are implementing TDE against a system with large databases where performance is critical then you will want to either run it in a period of quiet (or down time), or you will want to monitor to check that encryption isn’t impacting your system too much. Experience suggests that it shouldn’t be a problem unless your server is already under strain.

There are a few things to look out for if you are monitoring during the encryption scan:

  • CPU and IO, both these could take a hit
  • You may want to look out for blocking caused by encryption, you can do this by checking the sys.dm_tran_locks view where the resource_subtype is “ENCRYPTION_SCAN”. Here is an example of the SQL for that:

SELECT *
FROM sys.dm_tran_locks
WHERE resource_type = 'ENCRYPTION_SCAN';

  • Monitor transaction log usage with DBCC LOGINFO. While the encryption scanner is running the transaction log can’t be truncated and VLFs marked for re-use. This could mean the transaction log might grow larger than normal, so you need to watch out if you are constrained for disk space.
  • If your database is synched to a secondary in an HA scenario, for example as part of an Availability Group or through log shipping, you may want to check your synch process remains healthy during the encryption scan. We talk a little bit about working with TDE and HA later on in this series.

What if you run into any performance problems during the scan?

First things first – don’t turn encryption off.

ALTER DATABASE TestTDE SET ENCRYPTION OFF;

This isn’t going to stop the encryption scan, rather it’s just going to change direction. So now it will begin decrypting everything it’s just encrypted, that’s likely to have just as much impact, then sooner or later you’re going to have to start again.

What we want to do is to pause the encryption scan. Prior to SQL Server 2019 there was no direct command to achieve this, however there was a trace flag that could be used to achieve much the same thing. Let’s look at both methods. First, if you are on SQL Server 2017 or lower you can pause the encryption scan with the following command:

DBCC TRACEON(5004);

When you do this, if you then query dm_database_encryption_keys you will see the database is set to a state of 2 (Encryption in Progress) and the percent_complete column will show zero – as nothing is currently in progress.

When you wish to begin the scan again, you need to disable the trace flag and then set encryption on again (even though it’s not technically off):

DBCC TRACEOFF(5004,-1);
ALTER DATABASE TestTDE SET ENCRYPTION ON;

When you do this the scanner will pick up where it left off, for instance if it had got to 50%, then it will then continue from there.

It’s important to note that the trace flag doesn’t actually turn TDE off. In fact, if you add new data, or update data and it gets written to disk while the trace flag is enabled, the data will still become encrypted. The trace flag just pauses the background process of converting all the data already on disk.

Note that this method will pause the encryption scan for all databases that are in the process of being encrypted. The SQL 2019 method is better as it gives us the control to pause the scan for a specific database using the following code:

ALTER DATABASE TestTDE SET ENCRYPTION SUSPEND;

To set the encryption running again from where it left off, we just use the following command:

ALTER DATABASE TestTDE SET ENCRYPTION RESUME;

Just like with the trace flag, this method doesn’t turn TDE off, it just pauses the background process of encrypting existing data. New data will still be written to disk encrypted. 

Along with this new functionality, SQL 2019 also added extra columns to the dm_database_encryption_keys view to help you manage the process of pausing and resuming the encryption scan. These columns include encryption_scan_state_desc which will tell us the state of the scan, for instance if it is running or suspended. We also have encryption_scan_modify_date which tells us when the scan was last modified, we can use that to tell when a scan was suspended or resumed.

If performance impact is an issue for you with the scanning process, you can use one of these methods to incrementally run the scan out of hours, pausing it when you want to ensure maximum performance of your systems.

What if the Encryption Scan Fails?

 It is possible for the encryption scan to fail. The most likely scenario is a failure due to corruption in your database. Because the scan is a background process you won’t get an error message telling you that it has stopped, so it is good to use the methods we’ve looked at in this chapter to check when the scan is complete.

Prior to SQL 2019 a failure would exhibit itself by the encryption_state column showing as 2 (in progress) in dm_database_encryption_keys and the percent_complete column showing as zero. Usually the 5004 trace flag would also have been enabled to prevent the scan from resuming.

From SQL 2019 we have a little more information and can see in dm_database_encryption_keys that  encryption_scan_state_desc is set to aborted and can tell when that happened.

In either case your first action should be to check the database for corruption and resolve that if there are any issues. After that you can attempt to restart the encryption scan using the methods we’ve just looked at. If you have no corruption, and the scan still fails then you’ll need to reach out to Microsoft for support, but that’s an unlikely scenario.

Taking Backups While Encryption is in Progress

You can continue to take backups while the scanner is running to encrypt your existing data. However, it is important to understand that until that process is complete your backups will not be fully encrypted.

What will happen in the meantime is that a mixture of encrypted and unencrypted data will get written to your backup files. Only backups taken after the TDE encryption scan is complete will be fully protected.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

What is calling my T-SQL scalar function (millions of times)?

In this post we look at a method using Extended Events (XE) to identify what parent objects are calling a given SQL function and how often.

The background is that I was working with a team where we identified that a certain scalar function was being executed billions of time a day and – although lightweight for a single execution – overall it was consuming significant CPU on the server. We discussed a way of improving things but it required changing the code that called it. The problem was that the function was used in about 700 different places across the database code – both in stored procedures and views – though the views themselves would then be referenced by other stored procedures. Rather than update all the code they’d like to target the objects first that execute the function the most times.

The method I show here will identify the root calling object in each case and calculate the number of executions of the function that are instigated. It comes with a few caveats, I have to capture an event for all calls made on the database – as I don’t know which ones will result in a call to the function – that means there’s likely to be CPU overhead and if you have a large amount of calls occurring there could be a fair amount of disk consumption. In my test the Extended Events (XE) session consumed about 130MB of disk space for a million calls captured. In my case I’m talking billions of calls a day so that will be hundreds of GB. As such I plan to only run it for a small interval, starting with a minute to see what I get and will prefer to run it in a test environment with a representative load.

The method is going to use the module_start extended event and the causality tracking feature that allows you to track how events are related to each other. Let’s go ahead and create the session. First I click on Extended Events Sessions in SSMS then right-click and select “New Session”.

In the first page that comes up I just give the session a name and select to turn Causality Tracking on:

Then I click on events and select the event I want. In this case it is just the module_start event and I’m not applying any filters:

Final I configure my data storage. For this example I’ve just added a ring_buffer (memory) and an event_file allowing up to 10G of storage. When I run this for real I may need to allow quite a bit more storage.

Now we’re done and I can just click OK.

Then I can go the the XE session in SSMS, right-click and select “Start Session”.

In my test database I’m now going to run a few stored procedures that execute my function a number of times. The idea is that I’ll then be able to use the XE data to work out which stored procedure called it the most and that therefore (in a real scenario) I might want to focus on fixing first.

Having run my tests I can then stop the XE session and export the results to a table. I show the method for that in a previous post:

https://matthewmcgiffen.com/2018/08/08/exporting-extended-events-session-data-to-a-table/

I’ve exported the results into a new table called FunctionExecution in the same database. I show the structure of the table you get here:

The columns I’m interested in for this analysis are object_name (the name of the code object), attach_activity_id.guid (this comes from the causality tracking and will be the same for all objects in the same call stack) and attach_activity_id.seq (which shows the order in which objects were called).

In order to make the analysis quicker I also want to add couple of indexes. The object_name column is an nvarchar(max) which won’t support indexing, so first I create a new column with a better datatype and copy the values over:

ALTER TABLE dbo.FunctionExecution ADD ObjectName sysname;
UPDATE dbo.FunctionExecution SET ObjectName = CAST([object_name] AS sysname);

Then I create my indexes:

CREATE INDEX IX_ObjectName ON dbo.FunctionExecution(ObjectName) INCLUDE ([attach_activity_id.guid]);
CREATE INDEX IX_GUID ON dbo.FunctionExecution([attach_activity_id.guid]) INCLUDE (ObjectName,[attach_activity_id.seq]);

Finally I am ready to run a query to get the results. I search for the name of the function I am interested in, use attach_activity_id.guid to find other calls in the same call stack, then use attach_activity_id.seq to find the top parent (with a value of 1):

SELECT parent.ObjectName, COUNT(*) AS NumberOfExecutionsOfFunction
FROM dbo.FunctionExecution func
INNER JOIN dbo.FunctionExecution parent
ON func.[attach_activity_id.guid] = parent. [attach_activity_id.guid]
WHERE func.ObjectName = 'NonInlinable'
AND parent.[attach_activity_id.seq] = 1
GROUP BY parent.ObjectName;

Here are the results against the test procedures I executed while the XE session was running:

For this example we can see that I have stored procedure called ProcedureCallingFunctionALotOfTimes that is responsible for most of the calls to my function – so in theory I’d focus my development efforts there first.

Use this method with caution though, as mentioned at the start there may be a lot of overhead in capturing all these events of your server – be it on your own head if that causes problems!

On an unrelated note, my book on SQL Server encryption is now available. You can get a copy through the following link:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

How Long Will it Take to Encrypt Your Existing Data with TDE?

As we’ve seen in previous posts, the process of turning TDE on for an empty database with no data is instantaneous. Most of the time though you’ll be applying TDE to an existing system where you may have a large amount of data that needs to be encrypted.

The process of setting up TDE is the same whether you’ve just set up a new database, or whether you’re working with a live database. Once you turn encryption on, SQL Server will automatically begin the process of encrypting any data in your database. Be that one row or terabytes of data.

There is nothing extra you need to do to make that happen. However, there are some questions you should be asking. How long will it take to encrypt your database? What sort of overhead is that going to put on your server – particularly for a live system? What should you do if you run into any issues?

Win this post we’re going to look at the first of those questions, how you can get an estimate of how long it might take for the initial encryption of your database. If you want to follow the examples in this post then you should first set up TDE as shown in https://matthewmcgiffen.com/2023/01/06/setting-up-tde/

Benchmarking TDE Performance on Your Server

I’m going to load up my previously created TestTDE database with about 10GB of data so we can see how the encryption process performs. We’ll do this with TDE turned off and then turn it on once the data is loaded. I’m running this on a  reasonably quick laptop and it takes a couple of minutes to load the data. If you’ve been following through these examples on your own SQL Server, then first you’ll need to turn TDE off with the following SQL:

ALTER DATABASE TestTDE SET ENCRYPTION OFF;

Then we can load the dummy data with the following code:

USE TestTDE;
CREATE TABLE dbo.SomeData(Id INT IDENTITY(1,1), SomeText VARCHAR(255));
GO
INSERT INTO dbo.SomeData (SomeText)
SELECT TOP 1000000
('XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
FROM sys.objects a
CROSS JOIN sys.objects b
CROSS JOIN sys.objects c
CROSS JOIN sys.objects d;
GO 100

After I turn encryption on again, I’m going to run a query to monitor the progress of encryption – polling every 5 seconds. If you’re working through this example on your own machine, you’ll want to have the query ready to go before you turn encryption on.

The command to turn TDE on is as previously stated.

ALTER DATABASE TestTDE SET ENCRYPTION ON;

Then you can immediately execute this query to report the progress.

DECLARE @state tinyint;
DECLARE @encyrption_progress
TABLE(sample_time DATETIME, percent_complete DECIMAL(5,2))
SELECT @state = k.encryption_state
FROM sys.dm_database_encryption_keys k
INNER JOIN sys.databases d
ON k.database_id = d.database_id
WHERE d.name = 'TestTDE';
WHILE @state != 3
BEGIN
INSERT INTO @encyrption_progress(sample_time, percent_complete)
SELECT GETDATE(), percent_complete
FROM sys.dm_database_encryption_keys k
INNER JOIN sys.databases d
ON k.database_id = d.database_id
WHERE d.name = 'TestTDE';
WAITFOR delay '00:00:05';
SELECT @state = k.encryption_state
FROM sys.dm_database_encryption_keys k
INNER JOIN sys.databases d
ON k.database_id = d.database_id
WHERE d.name = 'TestTDE';
END
SELECT * FROM @encyrption_progress;

The following image shows the results from running this test on my laptop.

You can see it took about a minute to encrypt 10GB of data. Figures will be different on your hardware, but that gives us an idea of the order of magnitude involved. If that scaled up linearly then it might take between 1 and 2 hours to encrypt a terabyte of data. I’m working here with data on an SSD, if you’re using older style disks then it would take considerably longer. I’d recommend using this technique to benchmark how your hardware will perform before you turn encryption on for your production databases.

In the next post we’ll look at how you can monitor for problem during the encryption process and what to do if you encounter an issue.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

The Cost of not Following the Regulations Around Data

Brent Ozar shared in his weekly links this week a GDPR penalty tracker which makes for thought-provoking reading. Regular readers of this blog will know I have a keen interest in data protection and encryption – on which topic I’ve written a book – so it’s interesting so see some figures of what failing in those areas can cost you.

Here’s a link to the report, though it only goes as far as July 2022 at the time of writing:

https://www.enforcementtracker.com/

The biggest fines (both individually and in total) have been levied for improper use of data, with Amazon, WhatsApp, Google and Facebook topping the list. After that though we have fines for insufficient protection of data. In most cases this is where companies have had some form of data breach and the safeguards in place weren’t deemed sufficient. The largest fine in this case was against British Airways who were hacked in 2018 and they received a fine of over 22 million euros for the lack of safeguards. That was calculated as 1.5% of the company’s turnover in 2017.

In the case of British Airways, the problem was an application vulnerability but there have been other cases where the database (or backups) were accessed directly. In these cases, encryption would have prevented the attack and saved the companies in question fines as well as reputational damage. As I’ve mentioned elsewhere in this blog, the advances made to the encryption feature set by Microsoft over the last few releases to SQL Server make it a no-brainer to implement encryption on at least your most sensitive data.

Let’s look at some of the summary figures in a bit more detail. Here we see a table of the total fines levied by type of violation:

And the same information in a graph:

We can see the total fines are in the billions, with incorrect processing and inappropriate use of data receiving the highest penalties. Protection of data is of the most interest to me and that comes 4th with around 80 million euros of fines in total (that was across about 200 separate violations) – still a large figure.

Some of the areas that the violations cover are probably outside our remit as DBAs and architects, but in some cases we do have some responsibility for pushing to make sure things are doing correctly.

In terms of following data principles these include (but are not limited to) things like:

  • Data Retention – making sure that personally identifiable data is kept for no longer than required.
  • Data Minimization – making sure we only collect the data we legitimately need.
  • Making sure data is processed securely.
  • We have adequate protection against data loss – things such as backups and checking for corruption.

In terms of illegal data processing, we should call out if we think data is being used for something we don’t have permission to do.

Protection of data where it resides in the database is certainly something we have to own, and shout loudly if things are not being done correctly. This includes having appropriate access controls and thinking about whether it should be encrypted.

One other important takeaway from the GPR tracker is the fact that the number of fines being levied is increasing over time so following the rules around data is continuing to become more and more important.

I should state in closing that this is just a quick post on the subject, and you need to do your own research to understand the rules and how they apply to your role. Many of us (in Europe at least) will have looked at the GDPR in some detail before it came into place, and in many companies, there was flurry of activity to make sure things were up to code. We shouldn’t rest on our laurels though and need to continually think about this stuff.

Finally, if you’re not encrypting your data then you should seriously get that onto your roadmaps. Though of course I’m going to say that as I want you to buy my book!

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

Securing the Root Keys for TDE

In this quick post we’re going to look at an additional step you should take to secure your TDE databases. This is a step you won’t find in any other documentation on setting up TDE in SQL Server that I’ve seen, so it probably bears a little explaining.

We looked at the encryption hierarchy in earlier posts. Let’s look at that again to give us context for what we are about to discuss:

At every level in the diagram, the keys are securely encrypted by the level above. What concerns us here is the very top level in the diagram, the keys used by the DPAPI. These keys are unique to your server, but as they sit at the root level there is nothing left to encrypt them, so they have to be stored unencrypted somewhere.

They keys are held in the following directory on most Windows systems:
C:\Windows\System32\Microsoft\Protect\S-1-5-18

It’s not a trivial technical task, but if someone can access these keys as well as a copy of your database files (including the master database) – or a copy of your database backups including master, then it is possible for them to decrypt the chain of keys working from the SMK down and eventually be able to decrypt your TDE-protected data.

That means if someone has read access to the DPAPI keys then they could access your data. However, this is easy to protect against. You just need to secure the above directory to ensure that only Local Administrators, the LOCAL SYSTEM account and the SQL Server service account can read anything within it. You can do that by applying the appropriate file system permissions if they are not already in place.

In the next post we’ll start to look at things you want to consider when encrypting existing databases that contain data.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

Setting up TDE

Transparent Data Encryption (TDE) is one of the easiest ways of encrypting your data at rest. In the previous posts we looked at what TDE is and how it works.

In this post we go through the steps of setting TDE up. You can set up TDE when you first create a database (which we will look at in this post), or you can apply it to an existing database (which we’ll cover in posts I’ve got coming up). In the latter case, once TDE has been enabled it will encrypt your existing data in the background. In either case the steps are the same.

Creating the Keys and Certificate

The first step in setting up TDE is to create the required keys and certificate. We’re going to focus on the default encryption hierarchy we’ve already looked at where we have the Service Master Key (SMK) at the top level, which protects the Database Master Key (DMK) in the master database, in turn protecting a certificate and associated asymmetric key pair, also in the master database. Finally, at the bottom we have the Database Encryption Key (DEK) in the user database which is protected by the certificate’s asymmetric key.

The SMK always exists for a SQL Server instance, so we just need to create the objects underneath it in the hierarchy. If you are planning on using Extensible Key Management (EKM) for managing your keys, then some of these steps are unnecessary. We’ll cover EKM later on.

Creating the Database Master Key (DMK)

First of all you must have a DMK. This lives in the master database and you can only have one per instance of SQL Server. You can create a DMK with the following SQL command (substitute your own password):

USE master;
GO
CREATE MASTER KEY
ENCRYPTION BY PASSWORD = 'UseAStrongPasswordHere!£$7';

We’ve already mentioned that the DMK is encrypted by the SMK, so it’s reasonable to ask why in this command we must also specify encryption by a password. What happens when you create the DMK is that a key is generated, two encrypted copies of that key are then created and stored in the master database, one encrypted by the SMK, and one by the password specified (both encrypted using the AES_256 algorithm). Having the copy encrypted by the password is necessary where you might need to restore a backup of the master database (including the DMK) to a separate SQL Server instance where the original SMK will not be available. In general, you don’t need to do this to recover a TDE enabled database to a separate SQL Server instance as long as you have backups of the certificate and private key, however you may use the DMK for purposes other than TDE.

It is recommended you backup the DMK. In most cases this backup is not useful in the context of TDE, but as mentioned you may have other objects not related to TDE that depend on the DMK so it is good practice. Backing up the DMK is a single command:

BACKUP MASTER KEY TO FILE = 'C:\Test\MyDMK'  
ENCRYPTION BY PASSWORD = 'UseAnotherStrongPasswordHere!£$7';

Creating the Certificate

Next, we need to create a certificate for use by TDE. We do that with the following code:

USE master;
GO
CREATE CERTIFICATE MyTDECert
WITH SUBJECT = 'Certificate used for TDE in the TestTDE database';

This command tells SQL Server to generate a self-signed certificate and associated public\private key pair which can be used for asymmetric encryption. The private key will automatically be encrypted by the DMK. As mentioned previously, you can create a separate certificate for each database you wish to protect with TDE – or you could share the certificate between multiple databases. Having a separate certificate for each database minimizes the attack area if someone gets access to one of them, but you may choose to share the certificate between multiple databases on the same instance for ease of management. Make sure you give your certificate a meaningful and unique name as you may want at some point to migrate it to another server which might already have other certificates used for TDE. You wouldn’t want them to have the same name, and it is useful to easily be able to identify what each is for – for instance you may want to include a suffix to represent the environment the certificate belongs to.

These objects are absolutely critical in being able to encrypt and decrypt your data, so it is essential that you back them up. That can be achieved with the following SQL:

USE master;    
GO
BACKUP CERTIFICATE MyTDECert  
TO FILE = 'C:\Test\MyTDECert.cer' 
WITH PRIVATE KEY  

    FILE = 'C:\Test\MyTDECert_PrivateKeyFile.pvk', 
    ENCRYPTION BY PASSWORD = 'UseAStrongPasswordHereToo!£$7' 
);

This creates two backup files, one for the certificate and one for the private key. The private key is backed up encrypted by the password supplied. These files, and the password used to protect the private key, need to be stored securely. It is impossible to over-stress how important this is. The most common pitfall people fall into with TDE is needing to recover or restore a TDE-protected database and not knowing where to find these backups or what the password is. Particularly where the person who set TDE has left the organization. If the backup has not been taken, cannot be found, or you don’t have the password it was protected with, then you have the potential to permanently lose all data that has been protected by TDE. If you enter a new organization or role where you are responsible for TDE-protected databases, you should make sure you know where these items are stored or take your own backups if they can’t be produced.

We have seen a few cases in this post where we need to use a password to protect an object. If your organization doesn’t already use one, then you should consider using a password manager such as KeePass (many others exist) to manage your passwords securely and safely.

Creating the Database Encryption Key (DEK)

The DEK is what is actually used to encrypt and decrypt data stored in your TDE-protected database. The DEK is stored in the database itself (in the database root record) but is stored encrypted by the private key we created in the previous step. The DEK is a single key used for symmetric encryption, the same key is used to both encrypt and decrypt data. A symmetric key is used in this case as symmetric encryption is much faster than asymmetric, and we want our transparent encryption activities to occur with a minimum of overhead and latency.

Before we create the DEK we need a database we are going to protect with TDE. If you haven’t already created the TestTDE database then you can do so with the following SQL:

CREATE DATABASE TestTDE;

Now we can go ahead and create the DEK.

USE TestTDE;
GO
CREATE DATABASE ENCRYPTION KEY WITH ALGORITHM = AES_256
ENCRYPTION BY SERVER CERTIFICATE MyTDECert;

You can see we specify the algorithm – AES (Advanced Encryption Standard) with a 256-bit key is recommended. We also specify the certificate to be used which will identify the public/private key pair to be used to encrypt the DEK.

Unlike the other keys, you don’t need to backup the DEK as it is automatically included in any backups you take of the database itself.

Encrypting the Database

Encrypting the database is the simple action of turning encryption on for the database.

ALTER DATABASE TestTDE SET ENCRYPTION ON;

In this case we have just created a new empty database so there is no data to encrypt and the action is instantaneous. As we then start to add tables and data the data will be automatically encrypted as it is written to disk for the first time. Similarly, any backups taken, Full Log or Differential, will automatically be encrypted as they are written to disk.

In sys.databases you can see which databases have TDE turned on by looking at the is_encrypted column, you can query that as follows:

SELECT name
FROM sys.databases
WHERE is_encrypted = 1;

We can see the results of the query in this image:

We can see that both our TestTDE database and tempdb get encrypted. As discussed previously tempdb gets encrypted when any other database uses TDE. We can view more details about our TDE encrypted databases by looking at the sys.dm_database_encryption_keys view. Let’s query that view and look at some columns of interest.

SELECT
   d.name,
   k.encryption_state,
   k.encryptor_type,
   k.key_algorithm,
   k.key_length,
   k.percent_complete
FROM sys.dm_database_encryption_keys k
INNER JOIN sys.databases d
   ON k.database_id = d.database_id;

This image shows what I see if I executed this query before I turned encryption on.

We can see information about the DEK. We also see the encryption_state column which describes the current state of the database. The possible values you’ll see are:

  1. Unencrypted
  2. Encryption in progress
  3. Encrypted
  4. Key change in progress
  5. Decryption in progress
  6. Protection change in progress (this occurs where the object protecting the DEK is being changed)

  The below image shows what we see if we execute the query after encryption has been enabled:

We see that both my database and the tempdb database are now encrypted. We also see the percent_complete column, which confusingly says zero. This column only has meaning when an encryption state change is occurring. So, if the encryption state was 2 (encryption in progress) – then we would see a value here while the database was in the process of being encrypted. Here my database contained no data, so it was instantaneous to flip encryption on. This column becomes relevant when we are encrypting an existing database that has a reasonable amount of data, we’ll look at that shortly.

The query we’ve just looked at will work on all versions of SQL Server. From SQL 2019 however we have a few extra columns of information available to us in the sys.dm_database_encryption_keys view. In particular there is the column encryption_state_desc that give us a plaintext description of the encryption state.

That’s all there is to setting TDE up, in the next post we’ll look at an extra step you may wish to take to improve the security of your data.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

Identify Unused Indexes across all Databases

TODO: Can I just output the columns I care about to reduce the size, add SQL Version

I had a request regarding how to identify unused indexes across all databases on a SQL Server instance (rather than just the current one). I’ve written this script before so thought I’d post it up here on my blog for the future use of myself and others.

The script uses the undocumented sp_MSforeachdb internal stored procedure to iterate through all the databases (excluding the system ones) and store the results of a standard unused indexes script into a temp table. The table can then be queried to analyse the results.

This script comes with a caveat, that the sp_MSforeachdb procedure can be unreliable and on occasion skip databases so you should check that the results include all the databases you are interested in. A simple count of distinct database names, and comparing that against the number of databases on your instance should be sufficient.

If you are trying to analyse in the case where you have multiple instances of the same application database, e.g. one for each client, you can query the temp table to identify indexes that are unused for all clients.

Anyway here’s the script:

--Find unused indexes across all user databases
IF OBJECT_ID('tempdb..#UnusedIndexes') IS NOT NULL
DROP TABLE #UnusedIndexes;
SELECT TOP 0
DB_NAME() AS DatabaseName,
s.name AS SchemaName,
o.name AS TableName,
i.name AS IndexName,
iu.user_updates as IndexUpdates,
iu.user_lookups as UserLookups,
iu.user_seeks AS UserSeeks,
iu.user_scans as UserScans
INTO #UnusedIndexes
FROM sys.dm_db_index_usage_stats iu
INNER JOIN sys.objects o
ON iu.object_id = o.object_id
INNER JOIN sys.schemas s
ON o.schema_id = s.schema_id
INNER JOIN sys.indexes i
ON o.object_id = i.object_id
AND i.index_id = iu.index_id
WHERE i.is_primary_key = 0
AND i.is_unique = 0
AND iu.user_lookups = 0
AND iu.user_scans = 0
AND iu.user_seeks = 0;
EXEC sp_MSforeachdb '
USE [?]
IF DB_ID() > 4
BEGIN
INSERT INTO #UnusedIndexes
SELECT
DB_NAME() AS DatabaseName,
s.name AS SchemaName,
o.name AS TableName,
i.name AS IndexName,
iu.user_updates as IndexUpdates,
iu.user_lookups as UserLookups,
iu.user_seeks AS UserSeeks,
iu.user_scans as UserScans
FROM sys.dm_db_index_usage_stats iu
INNER JOIN sys.objects o
ON iu.object_id = o.object_id
INNER JOIN sys.schemas s
ON o.schema_id = s.schema_id
INNER JOIN sys.indexes i
ON o.object_id = i.object_id
AND i.index_id = iu.index_id
WHERE i.is_primary_key = 0
AND i.is_unique = 0
AND iu.user_lookups = 0
AND iu.user_scans = 0
AND iu.user_seeks = 0;
END'
SELECT * FROM #UnusedIndexes;
--DROP #UnusedIndexes;

Note: Partially in response to Jeff’s comment below. Proceed with caution before dropping any indexes the script identifies. Stats are only kelp since the last restart, so if that was recent then you may have required indexes that get listed. Also think about whether you might have any occasional processes, such as month, quarter, or year-end processing that will not have executed since that last restart and may require indexes.

On an unrelated note, my book on SQL Server encryption is now available. You can get a copy through the following link:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7

How Secure is TDE?

When we consider how secure a form of encryption is there are two things we want to consider.

  • What threat scenarios we are protected from.
  • How easy is it to break down the encryption.

Let’s discuss each of these in turn.

What are We Protected From?

TDE encrypts data stored on the file system, so it should be pretty clear that we are trying to protect ourselves from an attacker who gets access to our files. You would be right in suggesting that shouldn’t be allowed to happen. Access controls should be in place to prevent inappropriate access. The reality though is that sometimes we get hacked and someone is able to work around our access controls. Sometimes backup files are stored offsite with a different organization where we do not control the access. That is why we have encryption – encryption is an extra line of defense. TDE offers no protection however against individuals who have direct access to query the database.

Let’s say someone does get access to our files – does TDE mean we are still sufficiently protected?

The answer unfortunately is that it depends. If someone has managed to get admin access to your database server then if they are sufficiently motivated, they will be able to read your data. TDE only protects you against lower levels of access.

The fact that an admin can get around the protection is an inevitability of many forms of encryption. TDE is managed by an administrator who has the sysadmin permissions on the database instance. They can enable TDE, they can disable TDE. They can change keys or export existing ones with their own password – but also they have direct access to the data anyway, so they can just run queries to view data.

Not all users who have admin rights over the box will have admin rights over the SQL instance, but anyone who has admin rights over the box can add themselves as an admin of the instance – though that usually requires restarting the SQL instance.

There are also other ways an admin can extract the keys from the file system – this is more complicated, but can be done if someone is knowledgeable enough.

So TDE only offers a very specific, but still very important protection.  If you need more then you will have to consider other forms of protection – such as Always Encrypted – possibly in conjunction with TDE.

How Easy is It to Break Down the Encryption?

TDE implements symmetric key encryption using standard encryption algorithms based on AES (Advanced Encryption Standard). When you set up TDE you can specify which AES algorithm you wish to use, AES_128, AES_192 or AES_256. In each case the number specifies the length of the key to be used for encryption in bits. Currently the only known way to crack such encryption is by brute force, i.e. try all the possible keys until you get lucky.

Obviously the longer your key, the harder the encryption should be to break, however even for AES_128, estimations of how long it would take to break down the key by brute force vary between a thousand years, to numbers many times greater than the age of the universe – trillions of years.

The difference in those estimates is based on how we anticipate processing power to grow in the future. In particular, whether the development of quantum computing might allow such activities to be carried out millions or billions of times faster than with conventional processors.

Even with the lowest estimates AES_128 should theoretically be sufficient in most scenarios but most people go for AES-256 which requires the same number of operations squared to crack. I recommend using AES-256 which should remain safe even if we see a quantum leap in processing power that exceeds all current expectations.

Up to 2016, SQL also supported the TRIPLE_DES_3KEY encryption protocol. This is now generally not considered to be as secure as AES, and from SQL 2016 its use is deprecated. So, it is best if you stick to AES even if you are on an older version of SQL Server.

In the next post in this series we’ll look at setting TDE up.

This post is part of a comprehensive series on encryption in SQL Server. If you want it all in one go you can buy my book:

http://www.dpbolvw.net/click-100730415-12898971?url=https%3A%2F%2Flink.springer.com%2Fbook%2F10.1007%2F978-1-4842-8664-7