Transparent Data Encryption has been around for some time now, making sure that data in SQL Server as stored on disk is encrypted. When it was announced, this was incredibly exciting.
You see, by default, SQL Server data is not encrypted. If you open up the pages within a data file, you can read the data that's in there. Numbers are stored as hex, varchar strings are stored as readable values – it can be quite surprising to realise this. The first time you ever salvage an MDF file from a broken server, open up that file, and just start reading the data, you realise that the data in most databases is only as secure as the physical security of the disks – you can read data from that table whether or not your Windows login has access to it.
With Transparent Data Encryption, that MDF file is encrypted. It's only decrypted when it's pulled into RAM, where access to it is controlled by database permissions. If your access to a particular table has been denied, you're not getting to read that data out of RAM. When the power goes out, the decrypted data in RAM disappears – that's what RAM's like. It's a good thing. But TDE is across the whole database, whether you like it or not. And everyone who has access to the table can read it unencrypted, as if it's never been encrypted.
It's Transparent. It doesn't feel like it's encrypted, and as far any application can see, it's not. This only protects against the disk (or backup) being compromised.
And then there's the distrust of DBAs.
As someone who deals with sensitive data regularly, I can assure you that this is a very real concern. I've had police checks, to help make sure that I'm trustworthy – and I make a point of never looking myself up in customer databases (I know I must exist in some of my customers' databases – I receive bills from some of them even). I also have confidence that my employees at LobsterPot Solutions are all completely trustworthy, and that I'd throw the book at them if they ever broke that trust.
I've certainly been asked "How do I stop the DBA from being able to read the data?"
And that's where the problem is. The DBA is the guardian of your data. They're the person who makes sure that the database doesn't have corruption, who can defrag indexes, tune queries, and so on. The DBA should be trustworthy with the data. But what if that data contains the lottery numbers? What if that data involves national secrets? At what point is the sensitivity of the data way too great to be able to let Archbishop Desmond Tutu look after it, let alone Barry the DBA?
Now, I understand that a DBA might feel insulted that they're not trusted to read the data. They need to look after it, but they can't look at it. My take is that if I can be removed from suspicion if there's a leak, then great. I know I'm okay. The client should know I'm okay. But would a criminal investigation be able to remove me from suspicion? Not if I'm one of the only people that could read the data and know how to cover my tracks.
Transparent Data Encryption doesn't stop me from being able to read the data. Not at all. If I have access to query the table, it looks unencrypted to me.
Always Encrypted, in SQL Server 2016, does stop me though, if I don't have the ability to access the certificate which has protects the column master key. Always Encrypted stores encrypted data in the database file. It's encrypted in RAM, and while it's being sent across the network, only being decrypted by the application that has access to the certificate. Now, I know that as an administrator, I might be able to jump through a few hoops to be able to get access to it, but this could be handled by other people, who could deny my access to it.
This decryption is still transparent to the applications that use it – so the applications don't need to change, apart from telling the connection string to look out for it. The .Net 4.6 environment will handle the decryption without developers needing to code it specifically. Access to those applications can be controlled in other ways.
If you're needing to search by values that are encrypted, it might not be ideal for you. But for that data that you need to make sure even you can't read, this could be a really nice option. Roll on 2016!
PS: Another option is to build encryption functions into client applications, so that the applications encrypt everything, and handle everything well away from the database. We've been able to do this since applications first began, but when there are multiple applications, the coordination of keys can become problematic. What you get with SQL 2016 is the ability to do this centralised control over the encryption and decryption.