db4o still provides a solution for high-security encryption by allowing any user to choose his own encryption mechanism that he thinks he needs. The db4o file IO mechanism is pluggable and any fixed-length encryption mechanism can be added. All that needs to be done is to write an IoAdapter plugin for db4o file IO.
This is a lot easier than it sounds. Simply:
.NET: Db4o.Configure().Io(new MyEncryptionAdapter());
However, you'll have to keep in mind that db4o will write partial udates. For example, it may write a full object and then only modify one field entry later one. Therefore it is not sufficient to en-/decrypt each access in isolation. You'll rather have to make up a tiling structure that defines the data chunks that have to be en-/decrypted together.
Another method to inject encryption capabilities into db4o for instances of specific classes only is to implement and configure an en-/decrypting translator.
A community project containing an XTEA encryption IoAdapter implementation can be found here: