Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

https://github.com/google/fscrypt

Go tool for managing Linux filesystem encryption
https://github.com/google/fscrypt

argon2 cryptography ext4-filesystem filesystem filesystem-encryption golang pam-module

Last synced: about 1 month ago
JSON representation

Go tool for managing Linux filesystem encryption

Lists

README 

        
# fscrypt [![GitHub version](https://badge.fury.io/go/github.com%2Fgoogle%2Ffscrypt.svg)](https://github.com/google/fscrypt/releases)



[![Build Status](https://github.com/google/fscrypt/workflows/CI/badge.svg)](https://github.com/google/fscrypt/actions?query=workflow%3ACI+branch%3Amaster)

[![GoDoc](https://godoc.org/github.com/google/fscrypt?status.svg)](https://godoc.org/github.com/google/fscrypt)

[![Go Report Card](https://goreportcard.com/badge/github.com/google/fscrypt)](https://goreportcard.com/report/github.com/google/fscrypt)

[![License](https://img.shields.io/badge/LICENSE-Apache2.0-ff69b4.svg)](http://www.apache.org/licenses/LICENSE-2.0.html)



`fscrypt` is a high-level tool for the management of [Linux native filesystem

encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html).

`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`](https://github.com/google/fscryptctl).



To use `fscrypt`, you must have a filesystem that supports the Linux native

filesystem encryption API (which is also sometimes called "fscrypt"; this

documentation calls it "Linux native filesystem encryption" to avoid confusion).

Only certain filesystems, such as [ext4](https://en.wikipedia.org/wiki/Ext4) and

[f2fs](https://en.wikipedia.org/wiki/F2FS), support this API.  For a full list

of supported filesystems and how to enable encryption support on each one, see

[Runtime dependencies](#runtime-dependencies).



For the release notes, see the [NEWS file](NEWS.md).



## Table of contents



- [Alternatives to consider](#alternatives-to-consider)

- [Threat model](#threat-model)

- [Features](#features)

- [Building and installing](#building-and-installing)

- [Runtime dependencies](#runtime-dependencies)

- [Configuration file](#configuration-file)

- [Setting up `fscrypt` on a filesystem](#setting-up-fscrypt-on-a-filesystem)

- [Setting up for login protectors](#setting-up-for-login-protectors)

  - [Securing your login passphrase](#securing-your-login-passphrase)

  - [Enabling the PAM module](#enabling-the-pam-module)

    - [Enabling the PAM module on Debian or Ubuntu](#enabling-the-pam-module-on-debian-or-ubuntu)

	- [Enabling the PAM module on Arch Linux](#enabling-the-pam-module-on-arch-linux)

	- [Enabling the PAM module on other Linux distros](#enabling-the-pam-module-on-other-linux-distros)

  - [Allowing `fscrypt` to check your login passphrase](#allowing-fscrypt-to-check-your-login-passphrase)

- [Backup, restore, and recovery](#backup-restore-and-recovery)

- [Encrypting existing files](#encrypting-existing-files)

- [Example usage](#example-usage)

  - [Setting up fscrypt on a directory](#setting-up-fscrypt-on-a-directory)

  - [Locking and unlocking a directory](#locking-and-unlocking-a-directory)

  - [Protecting a directory with your login passphrase](#protecting-a-directory-with-your-login-passphrase)

  - [Changing a custom passphrase](#changing-a-custom-passphrase)

  - [Using a raw key protector](#using-a-raw-key-protector)

  - [Using multiple protectors for a policy](#using-multiple-protectors-for-a-policy)

- [Contributing](#contributing)

- [Troubleshooting](#troubleshooting)

  - [I changed my login passphrase, now all my directories are inaccessible](#i-changed-my-login-passphrase-now-all-my-directories-are-inaccessible)

  - [Directories using my login passphrase are not automatically unlocking](#directories-using-my-login-passphrase-are-not-automatically-unlocking)

  - [Getting "encryption not enabled" on an ext4 filesystem](#getting-encryption-not-enabled-on-an-ext4-filesystem)

  - [Getting "user keyring not linked into session keyring"](#getting-user-keyring-not-linked-into-session-keyring)

  - [Getting "Operation not permitted" when moving files into an encrypted directory](#getting-operation-not-permitted-when-moving-files-into-an-encrypted-directory)

  - [Getting "Package not installed" when trying to use an encrypted directory](#getting-package-not-installed-when-trying-to-use-an-encrypted-directory)

  - [Some processes can't access unlocked encrypted files](#some-processes-cant-access-unlocked-encrypted-files)

  - [Users can access other users' unlocked encrypted files](#users-can-access-other-users-unlocked-encrypted-files)

  - [Getting "Required key not available" when backing up locked encrypted files](#getting-required-key-not-available-when-backing-up-locked-encrypted-files)

  - [The reported size of encrypted symlinks is wrong](#the-reported-size-of-encrypted-symlinks-is-wrong)

- [Legal](#legal)



## Alternatives to consider



Operating-system level storage encryption solutions work at either the

filesystem or block device level.  [Linux native filesystem

encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html)

(the solution configured by `fscrypt`) is filesystem-level; it encrypts

individual directories.  Only file contents and filenames are encrypted;

non-filename metadata, such as timestamps, the sizes and number of files, and

extended attributes, is **not** encrypted.  Users choose which directories will

be encrypted, and with what keys.



Before using `fscrypt`, you should consider other solutions:



* [**dm-crypt/LUKS**](https://en.wikipedia.org/wiki/Dm-crypt) is block device

  level encryption: it encrypts an entire block device (and hence an entire

  filesystem) with one key.  Unlocking this key will unlock the entire block

  device.  dm-crypt/LUKS is usually configured using

  [cryptsetup](https://gitlab.com/cryptsetup/cryptsetup/-/wikis/home).



* [`systemd-homed`](https://systemd.io/HOME_DIRECTORY/) supports encrypting home

  directories using the same Linux native filesystem encryption API that

  `fscrypt` uses.  Note that while the `systemd-homed` documentation refers to

  this as fscrypt support, it does not use the `fscrypt` tool; directories set

  up using `systemd-homed` cannot be managed by `fscrypt` and vice versa.

  `systemd-homed` has better integration with systemd than `fscrypt` does.

  However, `systemd-homed` (as of systemd v255) uses the

  ["V1" Linux kernel encryption API](https://www.kernel.org/doc/html/v6.8/filesystems/fscrypt.html#limitations-of-v1-policies),

  while `fscrypt` perfers the "V2" API. The older API causes

  [known issues](#some-processes-cant-access-unlocked-encrypted-files), and

  migrating `systemd-home` to the "V2" API is tracked

  [in this `systemd` issue](https://github.com/systemd/systemd/issues/18280).

  Issues with `systemd-homed` should be reported to the systemd developers.



* [**eCryptfs**](https://en.wikipedia.org/wiki/ECryptfs) is an alternative

  filesystem-level encryption solution.  It is a stacked filesystem, which means

  it sits on top of a real filesystem, rather than being directly integrated

  into the real filesystem.  Stacked filesystems have a couple advantages (such

  as working on almost any real filesystem), but also some significant

  disadvantages.  eCryptfs is usually configured using

  [ecryptfs-utils](https://packages.debian.org/stretch/ecryptfs-utils).



* Some Linux filesystems support encryption natively, but not in a way that is

  compatible with the common API that `fscrypt` uses.  Examples of this are

  Bcachefs and ZFS.  (Note: ZFS is not part of the upstream kernel.)  Bcachefs

  encryption is similar to dm-crypt in that it encrypts the full filesystem with

  one key.  ZFS encryption operates on a per-dataset basis.  If you are using

  one of these filesystems, refer to the documentation for that filesystem.



Which solution to use?  Here are our recommendations:



* eCryptfs shouldn't be used, if at all possible.  eCryptfs's use of filesystem

  stacking causes a number of issues, and eCryptfs is no longer actively

  maintained.  The original author of eCryptfs recommends using Linux native

  filesystem encryption instead.  The largest users of eCryptfs (Ubuntu and

  Chrome OS) have switched to dm-crypt or Linux native filesystem encryption.



* If you need fine-grained control of encryption within a filesystem and you are

  using a filesystem that supports `fscrypt`, then use `fscrypt`, or `fscrypt`

  together with dm-crypt/LUKS.  If you don't need this, then use dm-crypt/LUKS.



  To understand this recommendation: consider that the main advantage of

  `fscrypt` is to allow different files on the same filesystem to be encrypted

  by different keys, and thus be unlockable, lockable, and securely deletable

  independently from each other.  Therefore, `fscrypt` is useful in cases such

  as:



    * Multi-user systems, since each user's files can be encrypted with their

      own key that is unlocked by their own passphrase.



    * Single-user systems where it's not possible for all files to have the

      strongest level of protection.  For example, it might be necessary for the

      system to boot up without user interaction.  Any files that are needed to

      do so can only be encrypted by a hardware-protected (e.g. TPM-bound) key

      at best.  If the user's personal files are located on the same filesystem,

      then with dm-crypt/LUKS the user's personal files would be limited to this

      weak level of protection.  With `fscrypt`, the user's personal files could

      be fully protected using the user's passphrase.



  `fscrypt` isn't very useful in the following cases:



    * Single-user systems where the user is willing to enter a strong passphrase

      at boot time to unlock the entire filesystem.  In this case, the main

      advantage of `fscrypt` would go unused, so dm-crypt/LUKS would be better

      as it would provide better security (due to ensuring that all files and

      all filesystem metadata are encrypted).



    * Any case where it is feasible to create a separate filesystem for every

      encryption key you want to use.



  Note: dm-crypt/LUKS and `fscrypt` aren't mutually exclusive; they can be used

  together when the performance hit of double encryption is tolerable.  It only

  makes sense to do this when the keys for each encryption layer are protected

  in different ways, such that each layer serves a different purpose.  A

  reasonable set-up would be to encrypt the whole filesystem with dm-crypt/LUKS

  using a TPM-bound key that is automatically unlocked at boot time, and also

  encrypt users' home directories with `fscrypt` using their login passphrases.



## Threat model



Like other storage encryption solutions (including dm-crypt/LUKS and eCryptfs),

Linux native filesystem encryption is primarily intended to protect the

confidentiality of data from a single point-in-time permanent offline compromise

of the disk.  For a detailed description of the threat model, see the [kernel

documentation](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#threat-model).



It's worth emphasizing that none of these encryption solutions protect unlocked

encrypted files from other users on the same system (that's the job of OS-level

access control, such as UNIX file permissions), or from the cloud provider you

may be running a virtual machine on.  By themselves, they also do not protect

from "evil maid" attacks, i.e. non-permanent offline compromises of the disk.



## Features



`fscrypt` is intended to improve upon the work in

[e4crypt](http://man7.org/linux/man-pages/man8/e4crypt.8.html) by providing a

more managed environment and handling more functionality in the background.

`fscrypt` has a [design document](https://goo.gl/55cCrI) specifying its full

architecture.  See also the [kernel documentation for Linux native filesystem

encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html).



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:



1. Your login passphrase, through [PAM](http://www.linux-pam.org/Linux-PAM-html).

   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](#setting-up-for-login-protectors).



2. A custom passphrase.  This passphrase is hashed with

   [Argon2id](https://en.wikipedia.org/wiki/Argon2), by default calibrated to

   use all CPUs and take about 1 second.



3. A raw key file.  See [Using a raw key protector](#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 fscrypt

*   `fscrypt encrypt DIRECTORY` - Encrypts an empty directory

*   `fscrypt unlock DIRECTORY` - Unlocks an encrypted directory

*   `fscrypt lock DIRECTORY` - Locks an encrypted directory

*   `fscrypt purge MOUNTPOINT` - Locks all encrypted directories on a filesystem

*   `fscrypt status [PATH]` - Gets detailed info about filesystems or paths

*   `fscrypt metadata` - Manages policies or protectors directly



See the example usage section below or run `fscrypt COMMAND --help` for more

information about each of the commands.



## Building and installing



`fscrypt` has a minimal set of build dependencies:

*   [Go](https://golang.org/doc/install) 1.18 or higher. Older versions may work

    but they are not tested or supported.

*   A C compiler (`gcc` or `clang`)

*   `make`

*   Headers for [`libpam`](http://www.linux-pam.org/).

    Install them with the appropriate package manager:

    - Debian/Ubuntu: `sudo apt install libpam0g-dev`

    - Red Hat: `sudo yum install pam-devel`

    - Arch: [`pam`](https://www.archlinux.org/packages/core/x86_64/pam/)

      package (usually installed by default)



Once all the dependencies are installed, clone the repository by running:

```shell

git clone https://github.com/google/fscrypt

```

Running `make` 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:

```shell

go install github.com/google/fscrypt/cmd/fscrypt@latest

```



See the `Makefile` for instructions on how to further customize the build.



## Runtime dependencies



To run, `fscrypt` needs the following libraries:

*   `libpam.so` (almost certainly already on your system)



In addition, `fscrypt` requires a filesystem that supports the Linux native

filesystem encryption API.  Currently, the filesystems that support this are:



* ext4, with upstream kernel v4.1 or later.  The kernel configuration must

  contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or

  `CONFIG_EXT4_ENCRYPTION=y` or `=m` (for older kernels).  The filesystem must

  also have the `encrypt` feature flag enabled; to enable this flag, see

  [here](#getting-encryption-not-enabled-on-an-ext4-filesystem).



* f2fs, with upstream kernel v4.2 or later.  The kernel configuration must

  contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or

  `CONFIG_F2FS_FS_ENCRYPTION=y` (for older kernels).  The filesystem must also

  have the `encrypt` feature flag enabled; this flag can be enabled at format

  time by `mkfs.f2fs -O encrypt` or later by `fsck.f2fs -O encrypt`.



* UBIFS, with upstream kernel v4.10 or later.  The kernel configuration must

  contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or

  `CONFIG_UBIFS_FS_ENCRYPTION=y` (for older kernels).



* CephFS, with upstream kernel v6.6 or later.  The kernel configuration must

  contain `CONFIG_FS_ENCRYPTION=y`.



* [Lustre](https://www.lustre.org/), with Lustre v2.14.0 or later.  For details,

  see the Lustre documentation.  Please note that Lustre is not part of the

  upstream Linux kernel, and its encryption implementation has not been reviewed

  by the authors of `fscrypt`.  Questions/issues about Lustre encryption should

  be directed to the Lustre developers.  Lustre version 2.14 does not encrypt

  filenames, even though it claims to, so v2.15.0 or later should be used.



To check whether the needed option is enabled in your kernel, run:

```shell

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.



If you configure `fscrypt` to use non-default features, other kernel

prerequisites may be needed too.  See [Configuration

file](#configuration-file).



## 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,

	"allow_cross_user_metadata": 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 to `fscrypt 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", "Adiantum", and

      "AES_256_HCTR2".  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](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#encryption-modes-and-usage)

      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 keyrings, rather than to user keyrings.

  This can solve [issues with processes being unable to access unlocked

  encrypted files](#some-processes-cant-access-unlocked-encrypted-files).

  However, it requires kernel v5.4 or later, and it makes unlocking and locking

  encrypted directories require root.  (The PAM module will still work.)



  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"`.



* "allow\_cross\_user\_metadata" specifies whether `fscrypt` will allow

  protectors and policies from other non-root users to be read, e.g. to be

  offered as options by `fscrypt encrypt`.  The default value is `false`, since

  other users might be untrusted and could create malicious files.  This can be

  set to `true` to restore the old behavior on systems where `fscrypt` metadata

  needs to be shared between multiple users.  Note that this option is

  independent from the permissions on the metadata files themselves, which are

  set to 0600 by default; users who wish to share their metadata files with

  other users would also need to explicitly change their mode to 0644.



## Setting up `fscrypt` on a filesystem



`fscrypt` needs some directories to exist on the filesystem on which encryption

will be used:



* `MOUNTPOINT/.fscrypt/policies`

* `MOUNTPOINT/.fscrypt/protectors`



(If login protectors are used, these must also exist on the root filesystem.)



To create these directories, run `fscrypt setup MOUNTPOINT`.  If MOUNTPOINT is

owned by root, as is usually the case, then this command will require root.



There will be one decision you'll need to make: whether non-root users will be

allowed to create `fscrypt` metadata (policies and protectors).



If you say `y`, then these directories will be made world-writable, with the

sticky bit set so that users can't delete each other's files -- just like

`/tmp`.  If you say `N`, then these directories will be writable only by root.



Saying `y` maximizes the usability of `fscrypt`, and on most systems it's fine

to say `y`.  However, on some systems this may be inappropriate, as it will

allow malicious users to fill the entire filesystem unless filesystem quotas

have been configured -- similar to problems that have historically existed with

other world-writable directories, e.g. `/tmp`.  If you are concerned about this,

say `N`.  If you say `N`, then you'll only be able to run `fscrypt` as root to

set up encryption on users' behalf, unless you manually set custom permissions

on the metadata directories to grant write access to specific users or groups.



If you chose the wrong mode at `fscrypt setup` time, you can change the

directory permissions at any time.  To enable single-user writable mode, run:



    sudo chmod 0755 MOUNTPOINT/.fscrypt/*



To enable world-writable mode, run:



    sudo chmod 1777 MOUNTPOINT/.fscrypt/*



## Setting up for login protectors



If you want any encrypted directories to be protected by your login passphrase,

you'll need to:



1. Secure your login passphrase (optional, but strongly recommended)

2. 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.



### Securing 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`.



### Enabling the PAM module



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.



#### Enabling the PAM module on Debian or Ubuntu



The official `libpam-fscrypt` package for Debian (and Debian derivatives such as

Ubuntu) will install a configuration file for [Debian's PAM configuration

framework](https://wiki.ubuntu.com/PAMConfigFrameworkSpec) 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`.



#### Enabling the PAM module on Arch Linux



On Arch Linux, follow the recommendations at the [Arch Linux

Wiki](https://wiki.archlinux.org/index.php/Fscrypt#Auto-unlocking_directories).



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`](#allowing-fscrypt-to-check-your-login-passphrase).



#### Enabling the PAM module on other Linux distros



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](http://www.linux-pam.org/Linux-PAM-html/sag-configuration-file.html).



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.



`pam_fscrypt.so` accepts several options:



* `debug`: print additional debug messages to the syslog.  All hook types accept

  this option.



* `unlock_only`: only unlock directories (at log-in); don't also lock them (at

  log-out).  This is only relevant for the "session" hook.  Note that in

  `fscrypt` v0.2.9 and earlier, unlock-only was the default behavior, and

  `lock_policies` needed to be specified to enable locking.



### Allowing `fscrypt` to check your login passphrase



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

```



## Backup, restore, and recovery



Encrypted files and directories can't be backed up while they are "locked", i.e.

while they appear in encrypted form.  They can only be backed up while they are

unlocked, in which case they can be backed up like any other files.  Note that

since the encryption is transparent, the files won't be encrypted in the backup

(unless the backup applies its own encryption).



For the same reason (and several others), an encrypted directory can't be

directly "moved" to another filesystem.  However, it is possible to create a new

encrypted directory on the destination filesystem using `fscrypt encrypt`, then

copy the contents of the source directory into it.



For directories protected by a `custom_passphrase` or `raw_key` protector, all

metadata needed to unlock the directory (excluding the actual passphrase or raw

key, of course) is located in the `.fscrypt` directory at the root of the

filesystem that contains the encrypted directory.  For example, if you have an

encrypted directory `/home/$USER/private` that is protected by a custom

passphrase, all `fscrypt` metadata needed to unlock the directory with that

custom passphrase will be located in `/home/.fscrypt` if you are using a

dedicated `/home` filesystem or in `/.fscrypt` if you aren't.  If desired, you

can back up the `fscrypt` metadata by making a copy of this directory, although

this isn't too important since this metadata is located on the same filesystem

as the encrypted directory(s).



`pam_passphrase` (login passphrase) protectors are a bit different as they are

always stored on the root filesystem, in `/.fscrypt`.  This ties them to the

specific system and ensures that each user has only a single login protector.

Therefore, encrypted directories on a non-root filesystem **can't be unlocked

via a login protector if the operating system is reinstalled or if the disk is

connected to another system** -- even if the new system uses the same login

passphrase for the user.



Because of this, `fscrypt encrypt` will automatically generate a recovery

passphrase when creating a login passphrase-protected directory on a non-root

filesystem.  The recovery passphrase is simply a `custom_passphrase` protector

with a randomly generated high-entropy passphrase.  Initially, the recovery

passphrase is stored in a file in the encrypted directory itself; therefore, to

use it you **must** record it in another secure location.  It is strongly

recommended to do this.  Then, if ever needed, you can use `fscrypt unlock` to

unlock the directory with the recovery passphrase (by choosing the recovery

protector instead of the login protector).



If you really want to disable the generation of a recovery passphrase, use the

`--no-recovery` option.  Only do this if you really know what you are doing and

are prepared for potential data loss.



Alternative approaches to supporting recovery of login passphrase-protected

directories include the following:



* Manually adding your own recovery protector, using

  `fscrypt metadata add-protector-to-policy`.



* Backing up and restoring the `/.fscrypt` directory on the root filesystem.

  Note that after restoring the `/.fscrypt` directory, unlocking the login

  protectors will require the passphrases they had at the time the backup was

  made **even if they were changed later**, so make sure to remember these

  passphrase(s) or record them in a secure location.  Also note that if the UUID

  of the root filesystem changed, you will need to manually fix the UUID in any

  `.fscrypt/protectors/*.link` files on other filesystems.



The auto-generated recovery passphrases should be enough for most users, though.



## Encrypting existing files



`fscrypt` isn't designed to encrypt existing files, as this presents significant

technical challenges and usually is impossible to do securely.  Therefore,

`fscrypt encrypt` only works on empty directories.



Of course, it is still possible to create an encrypted directory, copy files

into it, and delete the original files.  The `mv` command will even work, as it

will fall back to a copy and delete ([except on older

kernels](#getting-operation-not-permitted-when-moving-files-into-an-encrypted-directory)).

However, beware that due to the characteristics of filesystems and storage

devices, this may not properly protect the files, as their original contents may

still be forensically recoverable from disk even after being deleted.  It's

**much** better to encrypt files from the very beginning.



There are only a few cases where copying files into an encrypted directory can

really make sense, such as:



* The source files are located on an in-memory filesystem such as `tmpfs`.



* The confidentiality of the source files isn't important, e.g. they are

  system default files and the user hasn't added any personal files yet.



* The source files are protected by a different `fscrypt` policy, the old and

  new policies are protected by only the same protector(s), and the old policy

  uses similar strength encryption.



If one of the above doesn't apply, then it's probably too late to securely

encrypt your existing files.



As a best-effort attempt, you can use the `shred` program to try to erase the

original files.  Here are the recommended commands for "best-effort" encryption

of an existing directory named "dir":



```bash

mkdir dir.new

fscrypt encrypt dir.new

cp -a -T dir dir.new

find dir -type f -print0 | xargs -0 shred -n1 --remove=unlink

rm -rf dir

mv dir.new dir

```



However, beware that `shred` isn't guaranteed to be effective on all storage

devices and filesystems.  For example, if you're using an SSD, "overwrites" of

data typically go to new flash blocks, so they aren't really overwrites.



Note: for reasons similar to the above, changed or removed `fscrypt` protectors

aren't guaranteed to be forensically unrecoverable from disk either.  Thus, the

use of weak or default passphrases should be avoided, even if changed later.



## Example usage



All these examples assume there is an ext4 filesystem which supports

encryption mounted at `/mnt/disk`.  See

[here](#getting-encryption-not-enabled-on-an-ext4-filesystem) for how

to enable encryption support on an ext4 filesystem.



### Setting up fscrypt on a directory



```bash

# 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".

Allow users other than root to create fscrypt metadata on the root filesystem?

(See https://github.com/google/fscrypt#setting-up-fscrypt-on-a-filesystem) [y/N] y

Metadata directories created at "/.fscrypt", writable by everyone.



# Start using fscrypt with our filesystem

>>>>> sudo fscrypt setup /mnt/disk

Allow users other than root to create fscrypt metadata on this filesystem? (See

https://github.com/google/fscrypt#setting-up-fscrypt-on-a-filesystem) [y/N] y

Metadata directories created at "/mnt/disk/.fscrypt", writable by everyone.



# 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

```



#### Quiet version

```bash

>>>>> sudo fscrypt setup --quiet --force --all-users

>>>>> sudo fscrypt setup /mnt/disk --quiet --all-users

>>>>> echo "hunter2" | fscrypt encrypt /mnt/disk/dir1 --quiet --source=custom_passphrase  --name="Super Secret"

```



### Locking and unlocking a directory



```bash

# 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

```



#### Quiet version

```bash

>>>>> fscrypt lock /mnt/disk/dir1 --quiet

>>>>> echo "hunter2" | fscrypt unlock /mnt/disk/dir1 --quiet

```



### Protecting a directory with your login passphrase



First, ensure that you have properly [set up your system for login

protectors](#setting-up-for-login-protectors).



Then, you can protect directories with your login passphrase as follows:



```bash

# 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

```



#### Quiet version

```bash

>>>>> mkdir /mnt/disk/dir2

>>>>> echo "password" | fscrypt encrypt /mnt/disk/dir2 --source=pam_passphrase --quiet

```



### Changing a custom passphrase

```bash

# 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.

```



#### Quiet version

```bash

>>>>> printf "hunter2\nhunter3" | fscrypt metadata change-passphrase --protector=/mnt/disk:7626382168311a9d --quiet

```



### Using a raw key protector



`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](http://man7.org/linux/man-pages/man7/random.7.html) and

[some common myths](https://www.2uo.de/myths-about-urandom/).



```bash

# 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.

```



#### Quiet version

```bash

>>>>> head --bytes=32 /dev/urandom > secret.key

>>>>> fscrypt encrypt /mnt/disk/dir3 --key=secret.key --source=raw_key --name=Skeleton

```



### Using multiple protectors for a policy



`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.



```bash

# 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.

```



#### Quiet version

```bash

>>>>> 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

```



## Contributing



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.



## Troubleshooting



In general, if you are encountering issues with `fscrypt`,

[open an issue](https://github.com/google/fscrypt/issues/new), following the

guidelines in `CONTRIBUTING.md`. We will try our best to help.



#### I changed my login passphrase, now all my directories are inaccessible



Usually, the PAM module `pam_fscrypt.so` will automatically detect changes to a

user's login passphrase and update the user's `fscrypt` login protector so that

they retain access their login-passphrase protected directories.  However,

sometimes a user's login passphrase can become desynchronized from their

`fscrypt` login protector.  This can happen if `root` assigns the user a new

passphrase without providing the old one, if the user's login passphrase is

managed by an external system such as LDAP, if the PAM module is not installed,

or if the PAM module is not properly configured.  See [Enabling the PAM

module](#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

```



#### Directories using my login passphrase are not automatically unlocking



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 the following may

be causing the issue:



* The PAM module might not be configured correctly.  Ensure you have correctly

  [configured the PAM module](#enabling-the-pam-module).



* If your login passphrase recently changed, then it might have gotten out of

  sync with your login protector.  To fix this, [manually change your login

  protector's

  passphrase](#i-changed-my-login-passphrase-now-all-my-directories-are-inaccessible)

  to get it back in sync with your actual login passphrase.



* Due to a [bug in sshd](https://bugzilla.mindrot.org/show_bug.cgi?id=2548),

  encrypted directories won't auto-unlock when logging in with ssh using the

  `ChallengeResponseAuthentication` ssh authentication method, which is also

  called `KbdInteractiveAuthentication`.  This ssh authentication method

  implements password authentication by default, so it might appear similar to

  `PasswordAuthentication`.  However, only `PasswordAuthentication` works with

  `fscrypt`.  To avoid this issue, make sure that your `/etc/ssh/sshd_config`

  file contains `PasswordAuthentication yes`, `UsePAM yes`, and either

  `ChallengeResponseAuthentication no` or `KbdInteractiveAuthentication no`.



#### Getting "encryption not enabled" on an ext4 filesystem



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 (run

  `tune2fs -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 package `2.02-2` or

  later [*not* `2.02_beta*`], including the version in Ubuntu 18.04 and later,

  since the patch to support `encrypt` 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](#runtime-dependencies) for how to enable it.



#### Getting "user keyring not linked into session keyring"



Some older versions of Ubuntu didn't link the user keyring into the session

keyring, which caused problems with `fscrypt`.



To avoid this issue, upgrade to Ubuntu 20.04 or later.



#### Getting "Operation not permitted" when moving files into an encrypted directory



Originally, filesystems didn't return the correct error code when attempting to

rename unencrypted files (or files with a different encryption policy) into an

encrypted directory.  Specifically, they returned `EPERM` instead of `EXDEV`,

which caused `mv` to fail rather than fall back to a copy as expected.



This bug was fixed in version 5.1 of the mainline Linux kernel, as well as in

versions 4.4 and later of the LTS (Long Term Support) branches of the Linux

kernel; specifically v4.19.155, 4.14.204, v4.9.242, and v4.4.242.



If the kernel can't be upgraded, this bug can be worked around by explicitly

copying the files instead, e.g. with `cp`.



__IMPORTANT:__ Encrypting existing files can be insecure.  Before doing so, read

[Encrypting existing files](#encrypting-existing-files).



#### Getting "Package not installed" when trying to use an encrypted directory



Trying to create or open an encrypted file will fail with `ENOPKG` ("Package not

installed") when the kernel doesn't support one or more of the cryptographic

algorithms used by the file or its directory.  Note that `fscrypt encrypt` and

`fscrypt unlock` will still succeed; it's only using the directory afterwards

that will fail.



The kernel will always support the algorithms that `fscrypt` uses by default.

However, if you changed the contents and/or filenames encryption algorithms in

[`/etc/fscrypt.conf`](#configuration-file), then you may run into this issue.

To fix it, enable the needed `CONFIG_CRYPTO_*` options in your Linux kernel

configuration.  See the [kernel

documentation](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#encryption-modes-and-usage)

for details about which option(s) are required for each encryption mode.



#### Some processes can't access unlocked encrypted files



This issue is caused by a limitation in the original design of Linux native

filesystem encryption which made it difficult to ensure that all processes can

access unlocked encrypted files.  This issue can manifest in many ways, such as:



* SSH to a user with an encrypted home directory not working, even when that

  directory is already unlocked



* Docker containers being unable to access encrypted files that were unlocked

  from outside the container



* NetworkManager being unable to access certificates stored in the user's

  already-unlocked encrypted home directory



* Other system services being unable to access already-unlocked encrypted files



* `sudo` sessions being unable to access already-unlocked encrypted files



* A user being unable to access encrypted files that were unlocked by root



If an OS-level error is shown, it is `ENOKEY` ("Required key not available").



To fix this issue, first run `fscrypt status $dir`, where `$dir` is your

encrypted directory.  If the output contains `policy_version:2`, then your issue

is something else, so stop reading now.  If the output contains

`policy_version:1` or doesn't contain any mention of `policy_version`, then

you'll need to upgrade your directory(s) to policy version 2.  To do this:



1. Upgrade to Linux kernel v5.4 or later.



2. Upgrade to `fscrypt` v0.2.7 or later.



3. Run `sudo fscrypt setup --force`.



4. Re-encrypt your encrypted directory(s).  Since files cannot be (re-)encrypted

   in-place, this requires replacing them with new directories.  For example:

   ```

     fscrypt unlock dir  # if not already unlocked

     mkdir dir.new

     fscrypt encrypt dir.new

     cp -a -T dir dir.new

     find dir -type f -print0 | xargs -0 shred -n1 --remove=unlink

     rm -rf dir

     mv dir.new dir

   ```



   You don't need to create a new protector.  I.e., when `fscrypt encrypt` asks

   for a protector, just choose the one you were using before.



5. `fscrypt status` on your directory(s) should now show `policy_version:2`,

   and the issue should be gone.



Note that once your directories are using policy version 2, they will only be

usable with Linux kernel v5.4 and later and `fscrypt` v0.2.6 and later.  So be

careful not to downgrade your software past those versions.



This issue can also be fixed by setting `"use_fs_keyring_for_v1_policies": true`

in `/etc/fscrypt.conf`, as described in [Configuration

file](#configuration-file).  This avoids needing to upgrade directories to

policy version 2.  However, this has some limitations, and the same kernel and

`fscrypt` prerequisites still apply for this option to take effect.  It is

recommended to upgrade your directories to policy version 2 instead.



#### Users can access other users' unlocked encrypted files



This is working as intended.  When an encrypted directory is unlocked (or

locked), it is unlocked (or locked) for all users.  Encryption is not access

control; the Linux kernel already has many access control mechanisms, such as

the standard UNIX file permissions, that can be used to control access to files.



Setting the mode of your encrypted directory to `0700` will prevent users other

than the directory's owner and `root` from accessing it while it is unlocked.

In `fscrypt` v0.2.5 and later, `fscrypt encrypt` sets this mode automatically.



Having the locked/unlocked status of directories be global instead of per-user

may seem unintuitive, but it is actually the only logical way.  The encryption

is done by the filesystem, so in reality the filesystem either has the key or it

doesn't.  And once it has the key, any additional checks of whether particular

users "have" the key would be OS-level access control checks (not cryptography)

that are redundant with existing OS-level access control mechanisms.



Similarly, any attempt of the filesystem encryption feature to prevent `root`

from accessing unlocked encrypted files would be pointless.  On Linux systems,

`root` is usually all-powerful and can always get access to files in ways that

cannot be prevented, e.g. `setuid()` and `ptrace()`.  The only reliable way to

limit what `root` can do is via a mandatory access control system, e.g. SELinux.



The original design of Linux native filesystem encryption actually did put the

keys into per-user keyrings.  However, this caused a [massive number of

problems](#some-processes-cant-access-unlocked-encrypted-files), as it's

actually very common that encrypted files need to be accessed by processes

running under different user IDs -- even if it may not be immediately apparent.



#### Getting "Required key not available" when backing up locked encrypted files



Encrypted files can't be backed up while locked; you need to unlock them first.

For details, see [Backup, restore, and recovery](#backup-restore-and-recovery).



#### The reported size of encrypted symlinks is wrong



Originally, filesystems didn't conform to POSIX when reporting the size of

encrypted symlinks, as they gave the size of the ciphertext symlink target

rather than the size of the plaintext target.  This would make the reported size

of symlinks appear to be slightly too large when queried using ``lstat()`` or

similar system calls.  Most programs don't care about this, but in rare cases

programs can depend on the filesystem reporting symlink sizes correctly.



This bug was fixed in version 5.15 of the mainline Linux kernel, as well as in

versions 4.19 and later of the LTS (Long Term Support) branches of the Linux

kernel; specifically v5.10.63, v5.4.145, and v4.19.207.



If the kernel can't be upgraded, the only workaround for this bug is to update

any affected programs to not depend on symlink sizes being reported correctly.



## Legal



Copyright 2017 Google Inc. under the

[Apache 2.0 License](https://www.apache.org/licenses/LICENSE-2.0); see the

`LICENSE` file for more information.



Author: Joe Richey 



This is not an official Google product.