linux/Documentation/filesystems/ecryptfs.rst

.. SPDX-License-Identifier: GPL-2.0

======================================================
eCryptfs: A stacked cryptographic filesystem for Linux
======================================================

eCryptfs is free software. Please see the file COPYING for details.
For documentation, please see the files in the doc/ subdirectory.  For
building and installation instructions please see the INSTALL file.

:Maintainer: Phillip Hellewell
:Lead developer: Michael A. Halcrow <mhalcrow@us.ibm.com>
:Developers: Michael C. Thompson
             Kent Yoder
:Web Site: http://ecryptfs.sf.net

This software is currently undergoing development. Make sure to
maintain a backup copy of any data you write into eCryptfs.

eCryptfs requires the userspace tools downloadable from the
SourceForge site:

http://sourceforge.net/projects/ecryptfs/

Userspace requirements include:

- David Howells' userspace keyring headers and libraries (version
  1.0 or higher), obtainable from
  http://people.redhat.com/~dhowells/keyutils/
- Libgcrypt


.. note::

   In the beta/experimental releases of eCryptfs, when you upgrade
   eCryptfs, you should copy the files to an unencrypted location and
   then copy the files back into the new eCryptfs mount to migrate the
   files.


Mount-wide Passphrase
=====================

Create a new directory into which eCryptfs will write its encrypted
files (i.e., /root/crypt).  Then, create the mount point directory
(i.e., /mnt/crypt).  Now it's time to mount eCryptfs::

    mount -t ecryptfs /root/crypt /mnt/crypt

You should be prompted for a passphrase and a salt (the salt may be
blank).

Try writing a new file::

    echo "Hello, World" > /mnt/crypt/hello.txt

The operation will complete.  Notice that there is a new file in
/root/crypt that is at least 12288 bytes in size (depending on your
host page size).  This is the encrypted underlying file for what you
just wrote.  To test reading, from start to finish, you need to clear
the user session keyring:

keyctl clear @u

Then umount /mnt/crypt and mount again per the instructions given
above.

::

    cat /mnt/crypt/hello.txt


Notes
=====

eCryptfs version 0.1 should only be mounted on (1) empty directories
or (2) directories containing files only created by eCryptfs. If you
mount a directory that has pre-existing files not created by eCryptfs,
then behavior is undefined. Do not run eCryptfs in higher verbosity
levels unless you are doing so for the sole purpose of debugging or
development, since secret values will be written out to the system log
in that case.


Mike Halcrow
mhalcrow@us.ibm.com