Oracle has improved the AES encryption/decryption functions in MySQL 5.6.17. They improved it a lot and posted a blog which explains all the details.

If you would like to know more about encryption there are two resources I would recommend:

• The Code Book by Simon Singh. This is about the history of cryptography, but it also includes a lot of information about crypto which is currently in use. This is also a very entertaining read.
• Crypto 101, a free/opensource book which gives a intro to crypto. The webpage also has a video of the talk on which the book is based.

And if you're going to …

We just released our first alpha of Percona XtraBackup 2.1 for MySQL and with it we included the ability to encrypt backups on the fly (full documentation here). This feature is different than simply piping the backup stream through the openssl or gpg binaries, which is what some people have used in the past. A big benefit of using the built-in encryption is that multiple CPU cores can be used for encryption (with the --encrypt-threads option). You can also combine compression and encryption, each using multiple CPU cores.

One advantage of …

Learn how to encrypt/decrypt MySQL data using AES techniques by the following article Encrypt MySQL data using AES techniques