Security Handbook/Kernel security
This section is on securing the system's kernel.
The basic rule when configuring the kernel is to remove everything that you do not need. This will not only create a small kernel but also remove the vulnerabilities that may lie inside drivers and other features.
Also consider turning off loadable module support. Even though it is possible to add root kits without this features, it does make it harder for normal attackers to install root kits via kernel modules.
Kerneli is a patch that adds encryption to the existing kernel. By patching your kernel you will get new options such as cryptographic ciphers, digest algorithms and cryptographic loop filters.
The kerneli patch is currently not in a stable version for the latest kernel, so be careful when using it.