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Database Encryption, Part 3: Transparent Encryption

By Adrian Lane

In our previous post in this Database Encryption series (Introduction, Part 2) we provided a decision tree for selecting a database encryption strategy. Our goal in this process is to map the encryption selection process to the security threats to protect against. Yes, that sounds simple enough, but it is tough to wade through vendor claims, especially when everyone from network storage to database vendors claims to provide the same value. We need to understand how to deal with the threats conceptually before we jump into the more complex technical and operational issues that can confuse your choices. In this post we are going to dig into the first branch of the tree, Non-credentialed threats – protecting against attacks from the outside, rather than from authenticated database users. We call this “Transparent/External Encryption”, since we don’t have to muck with database user accounts, and the encryption can sometimes occur outside the datbase. Transparent Encryption won’t protect sensitive content in the database if someone has access to it thought legitimate credentials, but it will protect the information on storage and in archives, and provides a significant advantage as it is deployed independent of your business applications. If you need to protect things like credit card numbers where you need to restrict even an administrator’s ability to see them, this option isn’t for you. If you are only worried about lost media, stolen files, a compromised host platform, or insecure storage, then Transparent Encryption is a good option. By not having to muck around with the internal database structures and application logic, it often provides huge savings in time and investment over more involved techniques.

We have chosen the term Transparent Encryption, as many of the database vendors have, to describe the capability to encrypt data stored in the database without modification to the applications using that database. We’ve also added “External” to distinguish from external encryption at the file or media level. If you have a database then you already have access controls that protect that data from unwanted viewing through database communications. The database itself screens queries or applications to make sure that only appropriate users or groups are permitted to examine and use data. The threat we want to address here is protecting data from physical loss or theft (including some forms of virtual theft) through means that are outside the scope of access controls. Keep in mind that even though the data is “in” a database, that database maintains permanent records on disk drives, with data being archived to many different types of low cost, long term storage. There are many ways for data to be accessed without credentials being supplied at all. These are cases where the database engine is by-passed altogether – for example, examination of data on backup tapes, disks, offline redo log files, transaction logs, or any other place data resides on storage media.

Transparent/External Encryption for protecting database data uses the following techniques & technologies:

  • Native Database Object (Transparent) Encryption: Database management systems, such as Oracle, Microsoft SQL Server, and IBM DB2, include capabilities to encrypt either internal database objects (tables and other structures) or the data stores (files). These encryption operations are managed from within the database, using native encryption functions built into the database, with keys being stored internally by default. This is good overall option in many scenarios as long as performance meets requirements. Depending on the platform, you may be able to offload key management to an external key management solution. The disadvantage is that it is specific to each database platform, and isn’t always available.
  • External File/Folder Encryption: The database files are encrypted using an external (third party) file/folder encryption tool. Assuming the encryption is configured properly, this protects the database files from unauthorized access on the server and those files are typically still protected as they are backed up, copied, or moved. Keys should be stored off the server and no access provided to local accounts, which protect against the server becoming compromised by an external attacker. Some file encryption tools, such as Vormetric and BitArmor, can also restrict access to the protected files based on application. Thus only the database processes can access the file, and even if an attacker compromises the database’s user account, they will only be able to access the decrypted data through the database itself. File/folder encryption of the database files is a good option as long as performance is acceptable and keys can be managed externally. Any file/folder encryption tool supports this option (including Microsoft EFS), but performance needs to be tested since there is wide variation among the different tools. Remember that any replication or distribution of data handled from within the database won’t be protected unless you also encrypt those destinations.
  • Media encryption: This includes full drive encryption or SAN encryption; the entire storage media is encrypted, and thus the database files are protected. Depending on the method used and the specifics of your environment, this may or may not provide protection for the data as it moves to other data stores, including archival (tape) storage. For example, depending on your backup agent, you may be backing up the unencrypted files or the encrypted storage blocks. This is best suited for high performance databases where the primary concern is physical loss of the media (e.g., a database on a managed SAN where the service provider handles failed drives potentially containing sensitive data). Any media encryption product supports this option.

Which option to choose depends on your performance requirements, threat model, exiting architecture, and security requirements. Unless you have a high-performance system that exceeds the capabilities of file/folder encryption, we recommend you look there first. If you are managing heterogeneous databases, you will likely look at a third party product over native encryption. In both cases, it’s very important to use external key management and not allow access by any local accounts. We will outline selection criteria and use cases to support the decision process in a future post.

You will notice that, depending upon which technique you choose, the initiation of the encryption, the engine that performs the encryption, and the key management server may all reside in different places. In fact, the latter two techniques encrypt the database but are not in the database at all; the engine that performs the encryption, as well as the processes responsible for managing the encryption operations, are outside of the database. In all three cases encryption remains transparent to business processing functions. Using the three technology variables (eEngine location, key management location, and who orchestrates) we introduced in Part Two of this series will help guide you in differentiating vendor offerings, and understand the strengths and weaknesses of each variation.

Next up we will discuss the techniques for securing data against credentialed users and some implementation considerations for user encryption.

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