Trying to mount encrypted file system failing

Question

I had created an encrypted file system using the following commands:

# dd if=/dev/zero of=/opt/vol
# losetup -e aes /dev/loop0 /opt/vol
Password:
# mkfs.ext4 /dev/loop0

The above device was mounted as follows:

# mount -t ext4 -o loop -o rw -o encryption=aes /opt/vol /mnt/enc
Password:
# 

I used to store data in the mounted location (/mnt/enc). Recently I re-installed my OS. So, before that, I backed up the /opt/vol file elsewhere. After re-installing ubuntu 15.10, I copied the file back to the same location (/opt/vol). Then I tried remounting the same file in ubuntu 15.10 and noticed the below error:

# losetup_e -e aes /dev/loop0 /opt/vol
Password:
# mount_e -t ext4 -o loop -o rw -o encryption=aes /opt/vol /mnt/enc
lt-mount: wrong fs type, bad option, bad superblock on /dev/loop1,
   missing codepage or helper program, or other error
   In some cases useful info is found in syslog - try
   dmesg | tail or so
# dmesg | tail
[   81.215500] EXT4-fs (loop1): VFS: Can't find ext4 filesystem
[  235.538008] EXT4-fs (loop1): VFS: Can't find ext4 filesystem
[  348.594842] EXT4-fs (loop1): VFS: Can't find ext4 filesystem
#

I had to re-compile util-linux from source (version 2.22), as I found that '-e' option was not supported from util-linux-2.23 onwards as mentioned here. Hence after compiling, I linked the util-linux-2.22 losetup and mount binaries to losetup_e and mount_e respectively.

Answer 1

I have not come across this way of doing things, and I'm unable to reproduce how you tried to mount it (I use Ubuntu 14.04 LTS), however I believe I have a solution - this worked for me.

Instead of trying to mount the raw device, mount the loopback device, so to mount it:

losetup -e aes /dev/loop0 /opt/vol
mount /dev/loop0 /mnt/enc

I never knew that losetup could directly handle an encrypted device before - thats pretty cool, and would seem to add an amount of plausible deniability as the losetup command doesn't fail on wrong password - it just does not let you mount the filesystem as its scrambled if the password is wrong !