Bug#768577: systemd-cryptsetup handles keyfile differently from cryptsetup on plain mode

[Quentin Lefebvre]

I could provide a patch so that systemd-cryptsetup behaves the same way 
as cryptsetup.

But actually, there is even an easier way to solve this: change the 
'hash' parameter in /etc/crypttab to 'plain'.
Doing this, cryptdisks_{start,stop} scripts work well, and so do 
systemd-cryptsetup (as it will pass a NULL pointer as hash parameter to 
cryptsetup, which is also legacy cryptsetup's way to handle keyfile + 
hash in plain mode).

This is the correct /etc/crypttab:
vaioHDpart6c_home      /dev/sda6         /root/keys/home.key 
cipher=aes-xts-plain64,size=512,hash=plain,offset=0
instead of
vaioHDpart6c_home      /dev/sda6         /root/keys/home.key 
cipher=aes-xts-plain64,size=512,hash=sha512,offset=0

Note that the hash algorithm "sha512" was, in this case, just ignored. 
Maybe next versions of cryptsetup will change that.

Of course, don't forget the command:
update-initramfs -k all -u
after changing /etc/crypttab.

Thank you for your help.

Cheers,
Quentin