Recovering a LUKS encrypted partition from dump

Question

I did a Linux Mint 15 install on my notebook a couple of weeks ago, and chose to encrypt the whole disk. Yesterday I could no longer decrypt it (that is, it insisted that either the passphrase or options were wrong at boot time). Really needing the notebook to work ASAP, I booted from CD, made a dump of the partition (dd if=/dev/sda5 ..) to another computer and reinstalled from scratch.

I'm fairly certain I know the passphrase, and there's a week's worth of my work in there, so I'd like to try and attempt recovery. However, I have no idea how to proceed. Googling was not very useful, likely because I don't know enough about any of LUKS, cryptsetup or Mint to even make good queries. All I could find is stuff explaining I should give up..

So, given a "passphrase" and a really large file sda5.bin, what commands should I try? Or, alternatively, where can I find information on how Linux Mint does it? I'm also wondering where I could find some sort of a changelog/list of updates of Linux Mint, to see if any recent updates were related..

Answer 1

Oh, wow, it's been a while. If memory serves, it goes roughly like this:

losetup /dev/loop0 /path/to/sda5.bin
cryptsetup luksOpen /dev/loop0 foo
mount /dev/mapper/foo /mnt 

If the cryptsetup stage fails, it's likely because your passphrase really is wrong, or because the corresponding key slot has been accidentally deleted. In either case, you're hosed.