/etc/crypttabfrom my old install. After that I went about installing Mint 9, when the installer got to the partitioning section I used my boot and root partitions, but had it install home on a USBdrive and left the encrypted partition alone. The whole install process went fine I disconnected the USBdrive and did a restart. At reboot it came up my /home partition was missing or not ready. So I dropped into a root shell, the first thing I did was to edit
/etc/crypttab, in fstab I changed the entry for the my /home partition to reflect my encrypted partition. I then just copied all of the info from my old crypttab over since the new one was empty. I also had to create a dir in /dev/mapper
cryptsetup -v luksDump /dev/sda3
cryptsetup -v luksOpen /dev/sda3 home#this will create a entry in /dev/mapper called home
After I did this I rebooted it came up to unlock the LUKS partition, only issue I have is it try's to mount all of the partitions before I have finished imputing the passphrase. So I have to hit M which drops to a option for root console or ctrl+D. I hit ctrl+D and it open Mint. So I need to figure out how to pause the boot process while I enter the passphrase and then I will be good.
this blog gave me the biggest clues http://tuxtraining.com/2008/03/05/encrypted-root-file-system-during-install-in-opensuse-103
also some clues from here http://forums.fedoraforum.org/showthread.php?t=234383