encfs (1) - Linux Manuals
encfs: mounts or creates an encrypted virtual filesystem
NAME
encfs - mounts or creates an encrypted virtual filesystem
SYNOPSIS
encfs [--version] [-v|--verbose] [-c|--config] [-t|--syslogtag] [-s] [-f] [--annotate] [--standard] [--paranoia] [--insecure] [--reverse] [--reversewrite] [--extpass=program] [-S|--stdinpass] [--anykey] [--forcedecode] [-require-macs] [-i MINUTES|--idle=MINUTES] [-m|--ondemand] [--delaymount] [-u|--unmount] [--public] [--nocache] [--noattrcache] [--nodatacache] [--no-default-flags] [-o FUSE_OPTION] [-d|--fuse-debug] [-H|--fuse-help] rootdir mountPoint [-- [Fuse Mount Options]]DESCRIPTION
EncFS creates a virtual encrypted filesystem which stores encrypted data in the rootdir directory and makes the unencrypted data visible at the mountPoint directory. The user must supply a password which is used to (indirectly) encrypt both filenames and file contents.If EncFS is unable to find a supported filesystem at the specified rootdir, then the user will be asked if they wish to create a new encrypted filesystem at the specified location. Options will be presented to the user allowing some control over the algorithms to use. As EncFS matures, there may be an increasing number of choices.
OPTIONS
- --version
- Shows EncFS version. Using --verbose before --version may display additional information.
- -c, --config
- Causes EncFS to use the supplied file as the configuration file.
- -v, --verbose
- Causes EncFS to enable logging of various debug channels within EncFS. Normally these logging messages are disabled and have no effect. It is recommended that you run in foreground (-f) mode when running with verbose enabled.
- -t, --syslogtag
- This option allows to set the syslog tag which will be used when messages are logged via syslog. By default the syslog tag is set to encfs.
- -s
- The -s (single threaded) option causes EncFS to run in single threaded mode. By default, EncFS runs in multi-threaded mode. This option is used during EncFS development in order to simplify debugging and allow it to run under memory checking tools.
- -f
- The -f (foreground) option causes EncFS to run in the foreground. Normally EncFS spawns off as a daemon and runs in the background, returning control to the spawning shell. With the -f option, it will run in the foreground and any warning/debug log messages will be displayed on standard error. In the default (background) mode, all log messages are logged via syslog.
- --annotate
- Print annotation lines to stderr during configuration.
- --standard
-
If creating a new filesystem, this automatically selects standard configuration
options, to help with automatic filesystem creation. This is the set of
options that should be used unless you know what you're doing and have read the
documentation.
When not creating a filesystem, this flag does nothing.
- --paranoia
- Same as --standard, but for paranoia mode.
- --insecure
- Allows you to disable data encoding, thus to pass plain data as is. Fully discouraged of course!
- --reverse
-
Normally EncFS provides a plaintext view of data on demand: it stores
enciphered data and displays plaintext data. With --reverse it takes as
source plaintext data and produces enciphered data on-demand. This can be
useful for creating remote encrypted backups, where you do not wish to keep the
local files unencrypted.
For example, the following would create an encrypted view in /tmp/crypt-view.
encfs --reverse /home/me /tmp/crypt-viewYou could then copy the /tmp/crypt-view directory in order to have a copy of the encrypted data. You must also keep a copy of the file /home/me/.encfs6.xml which contains the filesystem information. Together, the two can be used to reproduce the unencrypted data:
ENCFS6_CONFIG=/home/me/.encfs6.xml encfs /tmp/crypt-view /tmp/plain-viewNow /tmp/plain-view contains the same data as /home/me
Note that --reverse mode only works with limited configuration options, so many settings may be disabled when used. Incompatible options as for now : Filename Initialization Vector Chaining and External IV Chaining.
- --reversewrite
- Same as --reverse but will allow writes, if possible (configuration must have UniqueIV disabled). Incompatible option : Per-File Initialization Vectors.
- --extpass=program
-
Specify an external program to use for getting the user password. When the
external program is spawned, the environment variable ``RootDir'' will be set to
contain the path to the root directory. The program should print the password
to standard output.
EncFS takes everything returned from the program to be the password, except for a trailing newline (\n) which will be removed.
For example, specifying --extpass=/usr/lib/ssh/ssh-askpass will cause EncFS to use ssh's password prompt program.
Note: EncFS reads at most 2k of data from the password program, and it removes any trailing newline. Versions before 1.4.x accepted only 64 bytes of text.
- -S, --stdinpass
-
Read password from standard input, without prompting. This may be useful for
scripting encfs mounts.
Note that you should make sure the filesystem and mount points exist first. Otherwise encfs will prompt for the filesystem creation options, which may interfere with your script.
- --anykey
-
Turn off key validation checking. This allows EncFS to be used with
secondary passwords. This could be used to store a separate set of files in an
encrypted filesystem. EncFS ignores files which do not decode properly, so
files created with separate passwords will only be visible when the filesystem
is mounted with their associated password.
Note that if the primary password is changed (using encfsctl), the other passwords will not be usable unless the primary password is set back to what it was, as the other passwords rely on an invalid decoding of the volume key, which will not remain the same if the primary password is changed.
Warning: Use this option at your own risk.
- --forcedecode
- This option only has an effect on filesystems which use MAC block headers. By default, if a block is decoded and the stored MAC doesn't match what is calculated, then an IO error is returned to the application and the block is not returned. However, by specifying --forcedecode, only an error will be logged and the data will still be returned to the application. This may be useful for attempting to read corrupted files.
- --require-macs
-
If creating a new filesystem, this forces block authentication code headers to
be enabled. When mounting an existing filesystem, this causes encfs to exit
if block authentication code headers are not enabled.
This can be used to improve security in case the ciphertext is vulnerable to tampering, by preventing an attacker from disabling MACs in the config file.
- -i, --idle=MINUTES
- Enable automatic unmount of the filesystem after a period of inactivity. The period is specified in minutes, so the shortest timeout period that can be requested is one minute. EncFS will not automatically unmount if there are files open within the filesystem, even if they are open in read-only mode. However simply having files open does not count as activity.
- -m, --ondemand
- Mount the filesystem on-demand. This currently only makes sense in combination with --idle and --extpass options. When the filesystem becomes idle, instead of exiting, EncFS stops allowing access to the filesystem by internally dropping its reference to it. If someone attempts to access the filesystem again, the extpass program is used to prompt the user for the password. If this succeeds, then the filesystem becomes available again.
- --delaymount
- Do not mount the filesystem when encfs starts; instead, delay mounting until first use. This option only makes sense with --ondemand.
- -u, --unmount
- Unmounts the specified mountPoint.
- --public
-
Attempt to make encfs behave as a typical multi-user filesystem. By default,
all FUSE based filesystems are visible only to the user who mounted them. No
other users (including root) can view the filesystem contents. The --public
option does two things. It adds the FUSE flags ``allow_other'' and
``default_permission'' when mounting the filesystem, which tells FUSE to allow
other users to access the filesystem, and to use the ownership permissions
provided by the filesystem. Secondly, the --public flag changes how encfs's
node creation functions work - as they will try and set ownership of new nodes
based on the caller identification.
Warning: In order for this to work, encfs must be run as root --- otherwise it will not have the ability to change ownership of files. I recommend that you instead investigate if the fuse allow_other option can be used to do what you want before considering the use of --public.
- --nocache
- Disable the kernel's cache of file attributes. Setting this option makes EncFS pass ``attr_timeout=0'' and ``entry_timeout=0'' to FUSE. This makes sure that modifications to the backing file attributes that occour outside EncFS show up immediately in the EncFS mount. The internal EncFS data cache is also disabled. The main use case for --nocache is reverse mode.
- --noattrcache
- Same as --nocache but for attributes only.
- --nodatacache
- Same as --nocache but for data only.
- --no-default-flags
-
Encfs adds the FUSE flags ``use_ino'' and ``default_permissions'' by default, as
of version 1.2.2, because that improves compatibility with some programs. If
for some reason you need to disable one or both of these flags, use the option
--no-default-flags.
The following command lines produce the same result:
encfs raw crypt encfs --no-default-flags raw crypt -- -o use_ino,default_permissions - -o FUSE_ARG
-
Pass through FUSE args to the underlying library. This makes it easy to
pass FUSE options when mounting EncFS via mount (and /etc/fstab). Eg:
mount encfs#/home/me-crypt /home/me -t fuse -o kernel_cacheNote that encfs arguments cannot be set this way. If you need to set encfs arguments, create a wrapper, such as encfs-reverse;
#!/bin/sh encfs --reverse "$@"Then mount using the script path
mount encfs-reverse#/home/me /home/me-crypt -t fuse - -d, --fuse-debug
- Enables debugging within the FUSE library. This should only be used if you suspect a problem within FUSE itself (not EncFS), as it generates a lot of low-level data and is not likely to be very helpful in general problem tracking. Try verbose mode (-v) first, which gives a higher level view of what is happening within EncFS.
- -H, --fuse-help
- Shows FUSE help.
- --
- The -- option tells EncFS to send any remaining arguments directly to FUSE. In turn, FUSE passes the arguments to fusermount. See the fusermount help page for information on available commands.
ENVIRONMENT VARIABLES
- ENCFS6_CONFIG
-
Which config file (typically named .encfs6.xml) to use.
By default, the config file is read from the encrypted directory.
Using this option allows to store the config file separated from the
encrypted files.
Warning: If you lose the config file, the encrypted file contents are irrecoverably lost. It contains the master key encrypted with your password. Without the master key, recovery is impossible, even if you know the password.
EXAMPLES
Create a new encrypted filesystem. Store the raw (encrypted) data in ``~/.crypt'' , and make the unencrypted data visible in ``~/crypt''. Both directories are in the home directory in this example. This example shows the full output of encfs as it asks the user if they wish to create the filesystem:
% encfs ~/.crypt ~/crypt
Directory "/home/me/.crypt" does not exist, create (y,n)?y
Directory "/home/me/crypt" does not exist, create (y,n)?y
Creating new encrypted volume.
Please choose from one of the following options:
enter "x" for expert configuration mode,
enter "p" for pre-configured paranoia mode,
anything else, or an empty line will select standard mode.
?>
Standard configuration selected.
Using cipher Blowfish, key size 160, block size 512
New Password: <password entered here>
Verify: <password entered here>
The filesystem is now mounted and visible in ~/crypt. If files are created there, they can be seen in encrypted form in ~/.crypt. To unmount the filesystem, use fusermount with the -u (unmount) option:
% fusermount -u ~/crypt
Another example. To mount the same filesystem, but have fusermount name the mount point '/dev/foo' (as shown in df and other tools which read /etc/mtab), and also request kernel-level caching of file data (which are both special arguments to fusermount):
% encfs ~/.crypt ~/crypt -- -n /dev/foo -c
Or, if you find strange behavior under some particular program when working in an encrypted filesystem, it may be helpful to run in verbose mode while reproducing the problem and send along the output with the problem report:
% encfs -v -f ~/.crypt ~/crypt 2> encfs-report.txt
In order to avoid leaking sensitive information through the debugging channels, all warnings and debug messages (as output in verbose mode) contain only encrypted filenames. You can use the encfsctl program's decode function to decode filenames if desired.
CAVEATS
EncFS is not a true filesystem. It does not deal with any of the actual storage or maintenance of files. It simply translates requests (encrypting or decrypting as necessary) and passes the requests through to the underlying host filesystem. Therefore any limitations of the host filesystem will be inherited by EncFS (or possibly be further limited).One such limitation is filename length. If your underlying filesystem limits you to N characters in a filename, then EncFS will limit you to approximately 3*(N-2)/4. For example if the host filesystem limits to 255 characters, then EncFS will be limited to 189 character filenames. This is because encrypted filenames are always longer than plaintext filenames.
FILESYSTEM OPTIONS
When EncFS is given a root directory which does not contain an existing EncFS filesystem, it will give the option to create one. Note that options can only be set at filesystem creation time. There is no support for modifying a filesystem's options in-place.If you want to upgrade a filesystem to use newer features, then you need to create a new filesystem and mount both the old filesystem and new filesystem at the same time and copy the old to the new.
Multiple instances of encfs can be run at the same time, including different versions of encfs, as long as they are compatible with the current FUSE module on your system.
A choice is provided for two pre-configured settings ('standard' and 'paranoia'), along with an expert configuration mode.
Standard mode uses the following settings:
Paranoia mode uses the following settings:
In the expert / manual configuration mode, each of the above options is
configurable. Here is a list of current options with some notes about what
they mean:
On a 1.6Ghz AMD 64 system, roughly 64k iterations of the key derivation
function can be handled in half a second. The exact number of iterations to
use is stored in the configuration file, as it is needed to remount the
filesystem.
If an EncFS filesystem configuration from 1.4.x is modified with version 1.5
(such as when using encfsctl to change the password), then the new PBKDF2
function will be used and the filesystem will no longer be readable by older
versions.
Blowfish is an 8 byte cipher - encoding 8 bytes at a time. AES is a 16 byte
cipher.
Having larger block sizes reduces the overhead of EncFS a little, but it can
also add overhead if your programs read small parts of files. In order to read
a single byte from a file, the entire block that contains that byte must be
read and decoded, so a large block size adds overhead to small requests. With
write calls it is even worse, as a block must be read and decoded, the change
applied and the block encoded and written back out.
The default is 512 bytes as of version 1.0. It was hard coded to 64 bytes in
version 0.x, which was not as efficient as the current setting for general
usage.
The advantage of block encoding mode is that filename lengths all come out as a
multiple of the cipher block size. This means that someone looking at your
encrypted data can't tell as much about the length of your filenames. It is
on by default, as it takes a similar amount of time to using the stream cipher.
However stream cipher mode may be useful if you want shorter encrypted
filenames for some reason.
Based on an underlying filesystem supporting a maximum of 255 characters in
filenames, here is the maximum possible filename length depending on the choosen
encoding scheme : stream (189), block (176), block32 (143). Note that we should
rather talk about bytes, when filenames contain special (multi-bytes) characters.
Prior to version 1.1, only stream encoding was supported.
With initialization vector chaining, each directory gets its own initialization
vector. So ``a/foo'' and ``b/foo'' will have completely different encoded names
for ``foo''. This features has almost no performance impact (for most
operations), and so is the default in all modes.
Note: One significant performance exception is directory renames. Since the
initialization vector for filename encoding depends on the directory path, any
rename requires re-encoding every filename in the tree of the directory being
changed. If there are thousands of files, then EncFS will have to do thousands
of renames. It may also be possible that EncFS will come across a file that it
can't decode or doesn't have permission to move during the rename operation, in
which case it will attempt to undo any changes it made up to that point and the
rename will fail.
With per-file initialization vectors, each file gets its own 64-bit random
initialization vector, so that each file is encrypted in a different way.
This option is enabled by default.
Reverse mode derivates IV from inode number, it may then change for example
when source files are copied from one FS to another.
When this option is enabled, the per-file initialization vector is encoded
using the initialization vector derived from the filename initialization vector
chaining code. This means that the data in a file becomes tied to the
filename. If an encrypted file is renamed outside of encfs, it will no longer
be decodable within encfs. Note that unless Block MAC headers are enabled, the
decoding error will not be detected and will result in reading random looking
data.
There is a cost associated with this. When External IV Chaining is enabled,
hard links will not be allowed within the filesystem, as there would be no way
to properly decode two different filenames pointing to the same data.
Also, renaming a file requires modifying the file header. So renames will only
be allowed when the user has write access to the file.
Because of these limits, this option is disabled by default for standard mode
(and enabled by default for paranoia mode).
This option may be incompatible with some cloud providers, as during a rename,
file's content changes, but not its timestamp. Due to this, file's changes may
no be correctly seen by cloud providers' sync programs. It is then not
recommended for cloud usage.
This adds substantial overhead (default being 8 bytes per filesystem block),
plus computational overhead, and is not enabled by default except in paranoia
mode.
When this is not enabled and if EncFS is asked to read modified or corrupted
data, it will have no way to verify that the decoded data is what was
originally encoded.
Enabled by default. Can be disabled in expert mode.
Some algorithms in EncFS are also meant to frustrate on-line attacks where
an attacker is assumed to be able to modify the files.
The most intrusive attacks, where an attacker has complete control of the
user's machine (and can therefore modify EncFS, or FUSE, or the kernel
itself) are not guarded against. Do not assume that encrypted files will
protect your sensitive data if you enter your password into a compromised
computer. How you determine that the computer is safe to use is beyond the
scope of this documentation.
That said, here are some example attacks and data gathering techniques on the
filesystem contents along with the algorithms EncFS supports to thwart them:
Site : https://vgough.github.io/encfs/.
Support, bug reports... : https://github.com/vgough/encfs.
Mailing list : none.
Cygwin, Windows ports : https://github.com/vgough/encfs/wiki.
Key Derivation Function
As of version 1.5, EncFS now uses PBKDF2 as the default key derivation
function. The number of iterations in the keying function is selected based on
wall clock time to generate the key. In standard mode, a target time of 0.5
seconds is used, and in paranoia mode a target of 3.0 seconds is used.
Attacks
The primary goal of EncFS is to protect data off-line. That is, provide a
convenient way of storing files in a way that will frustrate any attempt to
read them if the files are later intercepted.
DISCLAIMER
This library is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. Please refer to the ``COPYING'' file distributed with
EncFS for complete details.
AUTHORS
EncFS was written by Valient Gough <vgough [at] pobox.com>.