I have an encrypted disk attached via USB. After upgrading to Jessie, I'm not able to mount it any more, getting error
Check that kernel supports aes-xts-plain64 cipher (check syslog for more info)
I tried to load different modules in /lib/modules/*/kernel/crypto, but with no success.
After some searching and getting together multiple pieces of information, I found a solution. tl;dr:
sudo rpi-update 0764e7d78d30658f9bfbf40f8023ab95f952bcad
and reboot.
In more detail: On aes-xts-plain64 support on linux-lts-4.1.18-1 I found that the problem appears in 4.1.18. It's apparently a regression, here is the bug. Reverting to 4.1.17 fixes the problem.
Post Easiest way to upgrade/downgrade Raspberry Pi kernel describes how to do it. In particular, it's necessary to find the appropriate commit hash in https://github.com/Hexxeh/rpi-firmware/, which is 0764e7d7 for 4.1.17, and then use rpi-update to switch to it.