It's not faster than userspace, it's much slower normally. On special boards with crypto accelerators it can be faster, and there can be compliance reasons to want it. References: [1] https://www.chronox.de/libkcapi/html/ch01s02.html [2] https://lwn.net/Articles/410763/ [3] https://trac.gateworks.com/wiki/linux/encryption#PerformaceC...