The PBKDF2 in sys/geom/eli/pkcs5v2.c is around half the speed than it could be.
https://jbp.io/2015/08/11/pbkdf2-performance-matters/
Submitted by: Joe Pixton
Original Patch by: jmg
I cleaned up the patch to solve issues from files that have moved in the mean time
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202365