This blog post provides instructions and code for installing and implementing a kernel module on a Debian machine. It includes a Makefile for building and cleaning the module, and a C file for the actual code of the module. The code involves creating and manipulating a keyring and key in the Linux kernel. The module can be tested by inserting and removing it from the kernel. The post also includes a description of the variables and functions used in the code.
The kernel crypto API offers a rich set of cryptographic ciphers as well as other data transformation mechanisms and methods to invoke these. The kernel crypto API refers to all algorithms as “transformations”. Therefore, a cipher handle variable usually has the name “tfm”. Besides cryptographic operations, the kernel crypto API also knows compression transformations and handles them the same way as ciphers.