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ungeli

I recently started using geli-encrypted devices for offsite backups. However, I worry that in the event of a disaster I'm more likely to have a Linux machine on hand than a (k)FreeBSD machine, so I'd like to be able to read my backups.

To that end, I've written a Python program to extract the master key from a geli metadata block (geli-extract-mkey.py), and a C / openssl program which will decrypt blocks given the master key, optionally serving it as a block device via nbd on Linux.

These utilities have only been tested on a toy-sized AES-128-XTS volume that uses a password and no keyfiles. This is the only supported cipher type, and authentication is not supported. Only blocksize 4096 has been tested, and files less than 2^20 blocks (requiring multiple keys) also have not been tested.

Requirements

  • Gnu99-compatible C compiler (tested with gcc 4.8)
  • OpenSSL (recent version required for AES-128-XTS) (tested with 1.0.1e)
  • Python interpreter (tested with Python 2.7)
  • PyCrypto (tested with 2.6.1)
  • Optional: Linux (for network block device support)

Usage

The volumes I've tested this on so far are created with nearly-default parameters: geli init -s 4096 -J geli-password block-device which gives AES-128-XTR encryption and no authentication. This is probably the only type of volume that will work.

Edit geli-extract-mkey.py to change the volume, password (and, in theory, keyfiles), and run. It can take upwards of a minute to run the Python pkcsv2 algorithm, so I've hardcoded its output for the geli-test volume. Record the hex-format master key which is printed:

$ python geli-extract-mkey.py
...
master key is 3f6d1fc8c02fefd07b55df58f1b29065d2b7b35d5d861fe6509b934737...

Now you can decrypt with ungeli (specify the whole key, the "..." notation above and below is not magic):

$ make
$ ./ungeli -m 3f6d1fc8... -n 2 geli-test
                    GNU GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

 Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
...

You can also serve the decrypted contents via a network block device:

$ sudo ./ungeli -m 3f6d1fc8... geli-test /dev/nbd0 &
$ dd if=/dev/nbd0 bs=4096 count=2
                    GNU GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

 Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
...

If that volume happens to be a compatible zpool then you can mount it with zfsonlinux as readonly:

$ sudo ./ungeli -m 3f6d1fc8... geli-test /dev/nbd0 &
$ sudo zpool import -d /dev -o readonly=on npool
$ cat /npool/example/GPL-3
                    GNU GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

 Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
...

License

Copyright © 2013 Jeff Epler jepler@unpythonic.net

GPLv3+ with OpenSSL linking exception

When compiled and linked "This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/)".