This is the standard archlinux encrypt hook extended to support multiple encrypted devices via cryptsetup= cryptsetup1= cryptsetup2= etc.

Hopefully one day it will be merged with the normal archlinux cryptsetup package (ask for it [here](https://bugs.archlinux.org/task/23182)), until then it will be available via the aur here:

https://aur.archlinux.org/packages/cryptsetup-multidisk/