fscrypt
is a high-level tool for the management of Linux filesystem
encryption.
fscrypt
manages metadata, key generation, key wrapping, PAM integration, and
provides a uniform interface for creating and modifying encrypted directories.
For a small low-level tool that directly sets policies, see
fscryptctl
.
Note that the kernel part of fscrypt
(which is integrated into filesystems
such as ext4) is also sometimes referred to as "fscrypt". To avoid confusion,
this documentation instead calls the kernel part "Linux filesystem encryption".
To use fscrypt
, you must have a filesystem with encryption enabled and a
kernel that supports reading/writing from that filesystem. Currently,
ext4,
F2FS, and
UBIFS support Linux filesystem
encryption. Ext4 has supported Linux filesystem encryption
since v4.1, F2FS
added support in v4.2, and UBIFS
added support in v4.10. Other filesystems
may add support for native encryption in the future. Filesystems may
additionally require certain kernel configuration options to be set to use
native encryption. See Runtime Dependencies.
- Other encryption solutions
- Features
- Building and Installing
- Runtime Dependencies
- Configuration file
- Setting up for login protectors
- Note about stability
- Example Usage
- Contributing
- Troubleshooting
- I changed my login passphrase, now all my directories are inaccessible
- Directories using my login passphrase are not automatically unlocking.
- Getting "encryption not enabled" on an ext4 filesystem.
- Getting "Operation not permitted" when moving files into an encrypted directory.
- Can't log in with ssh even when user's encrypted home directory is unlocked
- Legal
It is important to distinguish Linux filesystem encryption from two other encryption solutions: eCryptfs and dm-crypt.
Currently, dm-crypt encrypts an entire block device with a single master key.
dm-crypt can be used with or without fscrypt
. All filesystem data (including
all filesystem metadata) is encrypted with this single key when using dm-crypt,
while fscrypt
only encrypts the filenames and file contents in a specified
directory. Note that using both dm-crypt and fscrypt
simultaneously will give
the protections and benefits of both; however, this may cause a decrease in your
performance, as file contents are encrypted twice.
One example of a reasonable setup could involve using dm-crypt with a TPM or
Secure boot key, while using fscrypt
for the contents of a home directory.
This would still encrypt the entire drive, but would also tie the encryption of
a user's personal documents to their passphrase.
On the other hand, eCryptfs is another form of filesystem encryption on Linux; it encrypts a filesystem directory with some key or passphrase. eCryptfs sits on top of an existing filesystem. This makes eCryptfs an alternative choice if your filesystem or kernel does not support native filesystem encryption.
Also note that fscrypt
does not support or setup either eCryptfs or dm-crypt.
For these tools, use
ecryptfs-utils for
eCryptfs or cryptsetup for dm-crypt.
fscrypt
is intended to improve upon the work in
e4crypt by providing a
more managed environment and handling more functionality in the background.
fscrypt
has a design document specifying its full
architecture. See also the kernel documentation for Linux filesystem
encryption.
Briefly, fscrypt
deals with protectors and policies. Protectors represent some
secret or information used to protect the confidentiality of your data. The
three currently supported protector types are:
-
Your login passphrase, through PAM. The included PAM module (
pam_fscrypt.so
) can automatically unlock directories protected by your login passphrase when you log in, and lock them when you log out. IMPORTANT: before using a login protector, follow Setting up for login protectors. -
A custom passphrase. This passphrase is hashed with Argon2id, by default calibrated to use all CPUs and take about 1 second.
-
A raw key file. See Using a raw key protector.
These protectors are mutable, so the information can change without needing to update any of your encrypted directories.
Policies represent the actual key passed to the kernel. This "policy key" is immutable and policies are (usually) applied to a single directory. Protectors then protect policies, so that having one of the protectors for a policy is enough to get the policy key and access the data. Which protectors protect a policy can also be changed. This allows a user to change how a directory is protected without needing to reencrypt the directory's contents.
Concretely, fscrypt
contains the following functionality:
fscrypt setup
- Creates/etc/fscrypt.conf
and the/.fscrypt
directory- This is the only functionality which always requires root privileges
fscrypt setup MOUNTPOINT
- Gets a filesystem ready for use with fscryptfscrypt encrypt DIRECTORY
- Encrypts an empty directoryfscrypt unlock DIRECTORY
- Unlocks an encrypted directoryfscrypt lock DIRECTORY
- Locks an encrypted directoryfscrypt purge MOUNTPOINT
- Locks all encrypted directories on a filesystemfscrypt status [PATH]
- Gets detailed info about filesystems or pathsfscrypt metadata
- Manages policies or protectors directly
The following functionality is planned:
fscrypt backup
- Manages backups of thefscrypt
metadatafscrypt recovery
- Manages recovery keys for directoriesfscrypt cleanup
- Scans filesystem for unused policies/protectors
See the example usage section below or run fscrypt COMMAND --help
for more
information about each of the commands.
fscrypt
has a minimal set of build dependencies:
- Go 1.11 or higher. Older versions may work but they are not tested or supported.
- A C compiler (
gcc
orclang
) make
- Headers for
libpam
. Install them with the appropriate package manager:- Debian/Ubuntu:
sudo apt install libpam0g-dev
- Red Hat:
sudo yum install pam-devel
- Arch:
pam
package (usually installed by default)
- Debian/Ubuntu:
Once all the dependencies are installed, you can get the repository by running:
go get -d github.com/google/fscrypt/...
Running make
in $GOPATH/src/github.com/google/fscrypt
builds the binary
(fscrypt
) and PAM module (pam_fscrypt.so
) in the bin/
directory.
Running sudo make install
installs fscrypt
into /usr/local/bin
,
pam_fscrypt.so
into /usr/local/lib/security
, and pam_fscrypt/config
into
/usr/local/share/pam-configs
.
On Debian (and Debian derivatives such as Ubuntu), use sudo make install PREFIX=/usr
to install into /usr
instead of the default of /usr/local
.
Ordinarily you shouldn't manually install software into /usr
, since /usr
is
reserved for Debian's own packages. However, Debian's PAM configuration
framework only recognizes configuration files in /usr
, not in /usr/local
.
Therefore, the PAM module will only work if you install into /usr
. Note: if
you later decide to switch to using the Debian package libpam-fscrypt
, you'll
have to first manually run sudo make uninstall PREFIX=/usr
.
It is also possible to use make install-bin
to only install the fscrypt
binary, or make install-pam
to only install the PAM files.
Alternatively, if you only want to install the fscrypt
binary to
$GOPATH/bin
, simply run:
go get github.com/google/fscrypt/cmd/fscrypt
See the Makefile
for instructions on how to further customize the build.
To run, fscrypt
needs the following libraries:
libpam.so
(almost certainly already on your system)
In addition, fscrypt
requires kernel support for encryption for your
filesystem, and for some filesystems that a feature flag has been
enabled in the on-disk filesystem superblock:
-
For ext4, the kernel must be v4.1 or later, and the kernel configuration must have either
CONFIG_FS_ENCRYPTION=y
(for kernels v5.1+) orCONFIG_EXT4_ENCRYPTION=y
or=m
(for older kernels). Also, the filesystem must have theencrypt
feature flag enabled; see here for how to enable it. -
For f2fs, the kernel must be v4.2 or later, and the kernel configuration must have either
CONFIG_FS_ENCRYPTION=y
(for kernels v5.1+) orCONFIG_F2FS_FS_ENCRYPTION=y
(for older kernels). Also, the filesystem must have theencrypt
feature flag enabled. It can be enabled at format time bymkfs.f2fs -O encrypt
, or later byfsck.f2fs -O encrypt
. -
For UBIFS, the kernel must be v4.10 or later, and the kernel configuration must have either
CONFIG_FS_ENCRYPTION=y
(for kernels v5.1+) orCONFIG_UBIFS_FS_ENCRYPTION=y
(for older kernels).
To check whether the needed option is enabled in your kernel, run:
zgrep -h ENCRYPTION /proc/config.gz /boot/config-$(uname -r) | sort | uniq
It is also recommended to use Linux kernel v5.4 or later, since this allows the use of v2 encryption policies. v2 policies have several security and usability improvements over v1 policies.
Be careful when using encryption on removable media, since filesystems with the
encrypt
feature cannot be mounted on systems with kernel versions older than
the minimums listed above -- even to access unencrypted files!
If you configure fscrypt
to use non-default features, other kernel
prerequisites may be needed too. See Configuration
file.
Running sudo fscrypt setup
will create the configuration file
/etc/fscrypt.conf
if it doesn't already exist. It's a JSON file
that looks like the following:
{
"source": "custom_passphrase",
"hash_costs": {
"time": "52",
"memory": "131072",
"parallelism": "32"
},
"options": {
"padding": "32",
"contents": "AES_256_XTS",
"filenames": "AES_256_CTS",
"policy_version": "2"
},
"use_fs_keyring_for_v1_policies": false
}
The fields are:
-
"source" is the default source for new protectors. The choices are "pam_passphrase", "custom_passphrase", and "raw_key".
-
"hash_costs" describes how difficult the passphrase hashing is. By default,
fscrypt setup
calibrates the hashing to use all CPUs and take about 1 second. The--time
option tofscrypt setup
can be used to customize this time when creating the configuration file. -
"options" are the encryption options to use for new encrypted directories:
-
"padding" is the number of bytes by which filenames are padded before being encrypted. The choices are "32", "16", "8", and "4". "32" is recommended.
-
"contents" is the algorithm used to encrypt file contents. The choices are "AES_256_XTS", "AES_128_CBC", and "Adiantum". Normally, "AES_256_XTS" is recommended.
-
"filenames" is the algorithm used to encrypt file names. The choices are "AES_256_CTS", "AES_128_CTS", and "Adiantum". Normally, "AES_256_CTS" is recommended.
To use algorithms other than "AES_256_XTS" for contents and "AES_256_CTS" for filenames, the needed algorithm(s) may need to be enabled in the Linux kernel's cryptography API. For example, to use Adiantum,
CONFIG_CRYPTO_ADIANTUM
must be set. Also, not all combinations of algorithms are allowed; for example, "Adiantum" for contents can only be paired with "Adiantum" for filenames. See the kernel documentation for more details about the supported algorithms. -
"policy_version" is the version of encryption policy to use. The choices are "1" and "2". If unset, "1" is assumed. Directories created with policy version "2" are only usable on kernel v5.4 or later, but are preferable to version "1" if you don't mind this restriction.
-
-
"use_fs_keyring_for_v1_policies" specifies whether to add keys for v1 encryption policies to the filesystem keyring, rather than to user keyrings. This can solve issues with processes being unable to access encrypted files. However, it requires kernel v5.4 or later, and it makes unlocking and locking encrypted directories require root.
The purpose of this setting is to allow people to take advantage of some of the improvements in Linux v5.4 on encrypted directories that are also compatible with older kernels. If you don't need compatibility with older kernels, it's better to not use this setting and instead (re-)create your encrypted directories with
"policy_version": "2"
.
If you want any encrypted directories to be protected by your login passphrase, you'll need to:
- Secure your login passphrase (optional, but strongly recommended)
- Enable the PAM module (
pam_fscrypt.so
)
If you installed fscrypt
from source rather than from your distro's package
manager, you may also need to allow fscrypt
to check your login passphrase.
Although fscrypt
uses a strong passphrase hash algorithm, the security of
login protectors is also limited by the strength of your system's passphrase
hashing in /etc/shadow
. On most Linux distributions, /etc/shadow
by default
uses SHA-512 with 5000 rounds, which is much weaker than what fscrypt
uses.
To mitigate this, you should use a strong login passphrase.
If using a strong login passphrase is annoying because it needs to be entered
frequently to run sudo
, consider increasing the sudo
timeout. That can be
done by adding the following to /etc/sudoers
:
Defaults timestamp_timeout=60
You should also increase the number of rounds that your system's passphrase
hashing uses (though this doesn't increase security as much as choosing a strong
passphrase). To do this, find the line in /etc/pam.d/passwd
that looks like:
password required pam_unix.so sha512 shadow nullok
Append rounds=1000000
(or another number of your choice; the goal is to make
the passphrase hashing take about 1 second, similar to fscrypt
's default):
password required pam_unix.so sha512 shadow nullok rounds=1000000
Then, change your login passphrase to a new, strong passphrase:
passwd
If you'd like to keep the same login passphrase (not recommended, as the old
passphrase hash may still be recoverable from disk), then instead run
sudo passwd $USER
and enter your existing passphrase. This re-hashes your
existing passphrase with the new rounds
.
To enable the PAM module pam_fscrypt.so
, follow the directions for your Linux
distro below. Enabling the PAM module is needed for login passphrase-protected
directories to be automatically unlocked when you log in (and be automatically
locked when you log out), and for login passphrase-protected directories to
remain accessible when you change your login passphrase.
The official libpam-fscrypt
package for Debian (and Debian derivatives such as
Ubuntu) will install a configuration file for Debian's PAM configuration
framework to
/usr/share/pam-configs/fscrypt
. This file contains reasonable defaults for
the PAM module. To automatically apply these defaults, run
sudo pam-auth-update
and follow the on-screen instructions.
This file also gets installed if you build and install fscrypt
from source,
but it is only installed to the correct location if you use make install PREFIX=/usr
to install into /usr
instead of the default of /usr/local
.
On Arch Linux, follow the recommendations at the Arch Linux Wiki.
We recommend using the Arch Linux package, either fscrypt
(official) or
fscrypt-git
(AUR). If you instead install fscrypt
manually using sudo make install
, then in addition to the steps on the Wiki you'll also need to create
/etc/pam.d/fscrypt
.
On all other Linux distros, follow the general guidance below to edit your PAM configuration files.
The fscrypt
PAM module implements the Auth, Session, and Password
types.
The Password functionality of pam_fscrypt.so
is used to automatically rewrap
a user's login protector when their unix passphrase changes. An easy way to get
the working is to add the line:
password optional pam_fscrypt.so
after pam_unix.so
in /etc/pam.d/common-password
or similar.
The Auth and Session functionality of pam_fscrypt.so
are used to automatically
unlock directories when logging in as a user, and lock them when logging out.
An easy way to get this working is to add the line:
auth optional pam_fscrypt.so
after pam_unix.so
in /etc/pam.d/common-auth
or similar, and to add the
line:
session optional pam_fscrypt.so
after pam_unix.so
in /etc/pam.d/common-session
or similar, but before
pam_systemd.so
or any other module that accesses the user's home directory or
which starts processes that access the user's home directory during their
session.
To make pam_fscrypt.so
print debugging messages to the system log, add the
debug
option. All hook types accept this option.
This step is only needed if you installed fscrypt
from source code.
Some Linux distros use restrictive settings in /etc/pam.d/other
that prevent
programs from checking your login passphrase unless a per-program PAM
configuration file grants access. This prevents fscrypt
from creating any
login passphrase-protected directories, even without auto-unlocking. To ensure
that fscrypt
will work properly (if you didn't install an official fscrypt
package from your distro, which should have already handled this), also create a
file /etc/pam.d/fscrypt
containing:
auth required pam_unix.so
fscrypt
follows semantic versioning. As such, all
versions below 1.0.0
should be considered development versions. This means no
guarantees are make about the stability of APIs or formats of config files. As
the on-disk metadata structures use Protocol
Buffers, we don't expect to break backwards
compatibility for metadata, but we give no guarantees.
All these examples assume there is an ext4 filesystem which supports
encryption mounted at /mnt/disk
. See
here for how
to enable encryption support on an ext4 filesystem.
# Check which directories on our system support encryption
>>>>> fscrypt status
filesystems supporting encryption: 1
filesystems with fscrypt metadata: 0
MOUNTPOINT DEVICE FILESYSTEM ENCRYPTION FSCRYPT
/ /dev/sda1 ext4 not enabled No
/mnt/disk /dev/sdb ext4 supported No
# Create the global configuration file. Nothing else necessarily needs root.
>>>>> sudo fscrypt setup
Defaulting to policy_version 2 because kernel supports it.
Customizing passphrase hashing difficulty for this system...
Created global config file at "/etc/fscrypt.conf".
Metadata directories created at "/.fscrypt".
# Start using fscrypt with our filesystem
>>>>> fscrypt setup /mnt/disk
Metadata directories created at "/mnt/disk/.fscrypt".
# Initialize encryption on a new empty directory
>>>>> mkdir /mnt/disk/dir1
>>>>> fscrypt encrypt /mnt/disk/dir1
The following protector sources are available:
1 - Your login passphrase (pam_passphrase)
2 - A custom passphrase (custom_passphrase)
3 - A raw 256-bit key (raw_key)
Enter the source number for the new protector [2 - custom_passphrase]: 2
Enter a name for the new protector: Super Secret
Enter custom passphrase for protector "Super Secret":
Confirm passphrase:
"/mnt/disk/dir1" is now encrypted, unlocked, and ready for use.
# We can see this created one policy and one protector for this directory
>>>>> fscrypt status /mnt/disk
ext4 filesystem "/mnt/disk" has 1 protector and 1 policy
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
POLICY UNLOCKED PROTECTORS
16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d
>>>>> sudo fscrypt setup --quiet --force
>>>>> fscrypt setup /mnt/disk --quiet
>>>>> echo "hunter2" | fscrypt encrypt /mnt/disk/dir1 --quiet --source=custom_passphrase --name="Super Secret"
# Write a file to our encrypted directory.
>>>>> echo "Hello World" > /mnt/disk/dir1/secret.txt
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: Yes
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
# Lock the directory. Note: if using a v1 encryption policy instead
# of v2, you'll need 'sudo fscrypt lock /mnt/disk/dir1 --user=$USER'.
>>>>> fscrypt lock /mnt/disk/dir1
"/mnt/disk/dir1" is now locked.
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: No
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
# Now the filenames and file contents are inaccessible
>>>>> ls /mnt/disk/dir1
u,k20l9HrtrizDjh0zGkw2dTfBkX4T0ZDUlsOhBLl4P
>>>>> cat /mnt/disk/dir1/u,k20l9HrtrizDjh0zGkw2dTfBkX4T0ZDUlsOhBLl4P
cat: /mnt/disk/dir1/u,k20l9HrtrizDjh0zGkw2dTfBkX4T0ZDUlsOhBLl4P: Required key not available
# Unlocking the directory makes the contents available
>>>>> fscrypt unlock /mnt/disk/dir1
Enter custom passphrase for protector "Super Secret":
"/mnt/disk/dir1" is now unlocked and ready for use.
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: Yes
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
>>>>> cat /mnt/disk/dir1/secret.txt
Hello World
>>>>> fscrypt lock /mnt/disk/dir1 --quiet
>>>>> echo "hunter2" | fscrypt unlock /mnt/disk/dir1 --quiet
First, ensure that you have properly set up your system for login protectors.
Then, you can protect directories with your login passphrase as follows:
# Select your login passphrase as the desired source.
>>>>> mkdir /mnt/disk/dir2
>>>>> fscrypt encrypt /mnt/disk/dir2
Should we create a new protector? [y/N] y
The following protector sources are available:
1 - Your login passphrase (pam_passphrase)
2 - A custom passphrase (custom_passphrase)
3 - A raw 256-bit key (raw_key)
Enter the source number for the new protector [2 - custom_passphrase]: 1
Enter login passphrase for joerichey:
"/mnt/disk/dir2" is now encrypted, unlocked, and ready for use.
# Note that the login protector actually sits on the root filesystem
>>>>> fscrypt status /mnt/disk/dir2
"/mnt/disk/dir2" is encrypted with fscrypt.
Policy: fe1c92009abc1cff4f3257c77e8134e3
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: Yes
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
6891f0a901f0065e Yes (/) login protector for joerichey
>>>>> fscrypt status /mnt/disk
ext4 filesystem "/mnt/disk" has 2 protectors and 2 policies
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
6891f0a901f0065e Yes (/) login protector for joerichey
POLICY UNLOCKED PROTECTORS
16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d
fe1c92009abc1cff4f3257c77e8134e3 Yes 6891f0a901f0065e
>>>>> fscrypt status /
ext4 filesystem "/" has 1 protector(s) and 0 policy(ies)
PROTECTOR LINKED DESCRIPTION
6891f0a901f0065e No login protector for joerichey
>>>>> mkdir /mnt/disk/dir2
>>>>> echo "password" | fscrypt encrypt /mnt/disk/dir2 --source=pam_passphrase --quiet
# First we have to figure out which protector we wish to change.
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: Yes
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
# Now specify the protector directly to the metadata command
>>>>> fscrypt metadata change-passphrase --protector=/mnt/disk:7626382168311a9d
Enter old custom passphrase for protector "Super Secret":
Enter new custom passphrase for protector "Super Secret":
Confirm passphrase:
Passphrase for protector 7626382168311a9d successfully changed.
>>>>> printf "hunter2\nhunter3" | fscrypt metadata change-passphrase --protector=/mnt/disk:7626382168311a9d --quiet
fscrypt
also supports protectors which use raw key files as the user-provided
secret. These key files must be exactly 32 bytes long and contain the raw binary
data of the key. Obviously, make sure to store the key file securely (and not in
the directory you are encrypting with it). If generating the keys on Linux make
sure you are aware of
how randomness works and
some common myths.
# Generate a 256-bit key file
>>>>> head --bytes=32 /dev/urandom > secret.key
# Now create a key file protector without using it on a directory. Note that we
# could also use `fscrypt encrypt --key=secret.key` to achieve the same thing.
>>>>> fscrypt metadata create protector /mnt/disk
Create new protector on "/mnt/disk" [Y/n] y
The following protector sources are available:
1 - Your login passphrase (pam_passphrase)
2 - A custom passphrase (custom_passphrase)
3 - A raw 256-bit key (raw_key)
Enter the source number for the new protector [2 - custom_passphrase]: 3
Enter a name for the new protector: Skeleton
Enter key file for protector "Skeleton": secret.key
Protector 2c75f519b9c9959d created on filesystem "/mnt/disk".
>>>>> fscrypt status /mnt/disk
ext4 filesystem "/mnt/disk" has 3 protectors and 2 policies
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
2c75f519b9c9959d No raw key protector "Skeleton"
6891f0a901f0065e Yes (/) login protector for joerichey
POLICY UNLOCKED PROTECTORS
16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d
fe1c92009abc1cff4f3257c77e8134e3 Yes 6891f0a901f0065e
# Finally, we could apply this key to a directory
>>>>> mkdir /mnt/disk/dir3
>>>>> fscrypt encrypt /mnt/disk/dir3 --protector=/mnt/disk:2c75f519b9c9959d
Enter key file for protector "Skeleton": secret.key
"/mnt/disk/dir3" is now encrypted, unlocked, and ready for use.
>>>>> head --bytes=32 /dev/urandom > secret.key
>>>>> fscrypt encrypt /mnt/disk/dir3 --key=secret.key --source=raw_key --name=Skeleton
fscrypt
supports the idea of protecting a single directory with multiple
protectors. This means having access to any of the protectors is sufficient to
decrypt the directory. This is useful for sharing data or setting up access
control systems.
# Add an existing protector to the policy for some directory
>>>>> fscrypt status /mnt/disk
ext4 filesystem "/mnt/disk" has 3 protectors and 3 policies
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
2c75f519b9c9959d No raw key protector "Skeleton"
6891f0a901f0065e Yes (/) login protector for joerichey
POLICY UNLOCKED PROTECTORS
d03fb894584a4318d1780e9a7b0b47eb No 2c75f519b9c9959d
16382f282d7b29ee27e6460151d03382 No 7626382168311a9d
fe1c92009abc1cff4f3257c77e8134e3 No 6891f0a901f0065e
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: No
Protected with 1 protector:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
>>>>> fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382
WARNING: All files using this policy will be accessible with this protector!!
Protect policy 16382f282d7b29ee27e6460151d03382 with protector 2c75f519b9c9959d? [Y/n]
Enter key file for protector "Skeleton": secret.key
Enter custom passphrase for protector "Super Secret":
Protector 2c75f519b9c9959d now protecting policy 16382f282d7b29ee27e6460151d03382.
>>>>> fscrypt status /mnt/disk/dir1
"/mnt/disk/dir1" is encrypted with fscrypt.
Policy: 16382f282d7b29ee27e6460151d03382
Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2
Unlocked: No
Protected with 2 protectors:
PROTECTOR LINKED DESCRIPTION
7626382168311a9d No custom protector "Super Secret"
2c75f519b9c9959d No raw key protector "Skeleton"
# Now the unlock command will prompt for which protector we want to use
>>>>> fscrypt unlock /mnt/disk/dir1
The available protectors are:
0 - custom protector "Super Secret"
1 - raw key protector "Skeleton"
Enter the number of protector to use: 1
Enter key file for protector "Skeleton": secret.key
"/mnt/disk/dir1" is now unlocked and ready for use.
# The protector can also be removed from the policy (if it is not the only one)
>>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382
WARNING: All files using this policy will NO LONGER be accessible with this protector!!
Stop protecting policy 16382f282d7b29ee27e6460151d03382 with protector 2c75f519b9c9959d? [y/N] y
Protector 2c75f519b9c9959d no longer protecting policy 16382f282d7b29ee27e6460151d03382.
>>>>> echo "hunter2" | fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 --key=secret.key --quiet
>>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 --quiet --force
We would love to accept your contributions to fscrypt
. See the
CONTRIBUTING.md
file for more information about signing the CLA and submitting
a pull request.
In general, if you are encountering issues with fscrypt
,
open an issue, following the
guidelines in CONTRIBUTING.md
. We will try our best to help.
The PAM module pam_fscrypt.so
should automatically detect changes to a user's
login passphrase so that they can still access their encrypted directories.
However, sometimes a user's login passphrase can become desynchronized from
their login protector. This can happen if their login passphrase is managed by
an external system, if the PAM module is not installed, or if the PAM module is
not properly configured. See Enabling the PAM
module for how to configure the PAM module.
To fix a user's login protector, find the corresponding protector ID by running
fscrypt status "/"
. Then, change this protector's passphrase by running:
fscrypt metadata change-passphrase --protector=/:ID
First, directories won't unlock if your session starts without password
authentication. The most common case of this is public-key ssh login. To
trigger a password authentication event, run su $USER -c exit
.
If your session did start with password authentication, then either the PAM module is not correctly installed and configured, or your login passphrase changed and got out of sync with your login protector. Ensure you have correctly configured the PAM module. Then, if necessary, manually change your login protector's passphrase to get it back in sync with your actual login passphrase.
This is usually caused by your ext4 filesystem not having the encrypt
feature
flag enabled. The encrypt
feature flag allows the filesystem to contain
encrypted files. (It doesn't actually encrypt anything by itself.)
Before enabling encrypt
on your ext4 filesystem, first ensure that all of the
following are true for you:
-
You only need to use your filesystem on kernels v4.1 and later.
(Kernels v4.0 and earlier can't mount ext4 filesystems that have the
encrypt
feature flag.) -
Either you only need to use your filesystem on kernels v5.5 and later, or your kernel page size (run
getconf PAGE_SIZE
) and filesystem block size (runtune2fs -l /dev/device | grep 'Block size'
) are the same.(Both values will almost always be 4096, but they may differ if your filesystem is very small, if your system uses the PowerPC CPU architecture, or if you overrode the default block size when you created the filesystem. Only kernels v5.5 and later support ext4 encryption in such cases.)
-
Either you aren't using GRUB to boot directly off the filesystem in question, or you are using GRUB 2.04 or later.
(Old versions of GRUB can't boot from ext4 filesystems that have
encrypt
enabled. If, like most people, you have a separate/boot
partition, you are fine. You are also fine if you are using the GRUB Debian package2.02-2
or later [not2.02_beta*
], including the version in Ubuntu 18.04 and later, since the patch to supportencrypt
was backported.)
After verifying all of the above, enable encrypt
by running:
tune2fs -O encrypt /dev/device
If you need to undo this, first delete all encrypted files and directories on the filesystem. Then, run:
fsck -fn /dev/device
debugfs -w -R "feature -encrypt" /dev/device
fsck -fn /dev/device
If you've enabled encrypt
but you still get the "encryption not enabled"
error, then the problem is that ext4 encryption isn't enabled in your kernel
config. See Runtime Dependencies for how to enable it.
This occurs when the kernel version is older than v5.1 and the source files are on the same filesystem and are either unencrypted or are in a different encrypted directory hierarchy.
Solution: copy the files instead, e.g. with cp
.
mv
works on kernels v5.1 and later, since those kernels return the correct
error code to make mv
fall back to a copy itself.
HOWEVER: in either case, it is important to realize that the original files may remain recoverable from free space on the disk after they are deleted. It's much better to keep all files encrypted from the very beginning.
As a last resort, the shred
program may be used to try to overwrite the
original files, e.g.:
cp file encrypted_dir/
shred -u file
However, shred
isn't guaranteed to be effective on all filesystems and storage
devices.
This is caused by a limitation in the original design of Linux filesystem encryption which made it difficult to ensure that all processes can access unlocked encrypted files. This issue can also manifest in other ways such as Docker containers being unable to access encrypted files, or NetworkManager being unable to access certificates if they are located in an encrypted directory.
The recommended way to fix this is by creating your encrypted
directories using v2 encryption policies rather than v1. This
requires Linux v5.4 or later and fscrypt
v0.2.6 or later. If these
prerequisites are met, enable v2 policies for new directories by
setting "policy_version": "2"
in /etc/fscrypt.conf
. For example:
"options": {
"padding": "32",
"contents": "AES_256_XTS",
"filenames": "AES_256_CTS",
"policy_version": "2"
},
This only affects new directories. If you want to upgrade an existing
encrypted directory to use a v2 policy, you'll need to re-create it by
using fscrypt encrypt
to encrypt a new empty directory, copying your
files into it, and replacing the original directory with it.
In fscrypt
v0.2.7 and later, the fscrypt setup
command
automatically sets "policy_version": "2"
when creating
/etc/fscrypt.conf
if kernel support is present.
IMPORTANT: directories that use v2 encryption policies are
unusable on Linux v5.3 and earlier. If this will be a problem for you
(for example, if your encrypted directories are on removable storage
that needs to work on computers with both old and new kernels), you'll
need to use v1 policies instead. In this case, you can enable a
fallback option to make fscrypt
use the filesystem keyring for v1
policies:
"use_fs_keyring_for_v1_policies": true
This fallback option only has an effect if the kernel supports using
the filesystem keyring. This option is also useful if you simply
don't want to re-create your old, v1 directories. However, this
option makes manually unlocking and locking encrypted directories
start to require root. (The PAM module will still work.) E.g.,
you'll need to run sudo fscrypt unlock
, not fscrypt unlock
. Most
people should just use v2 policies instead.
Copyright 2017 Google Inc. under the
Apache 2.0 License; see the
LICENSE
file for more information.
Author: Joe Richey joerichey@google.com
This is not an official Google product.