RencFs

⚠️ Warning This is early in development. Please do not use it with sensitive data just yet. Please wait for a stable release. It's mostly ideal for experimental and learning projects.

An encrypted file system that mounts with FUSE on Linux. It can be used to create encrypted directories.

You can then safely backup the encrypted folder on an untrusted server without worrying about the data being exposed.
You can also store it in any cloud storage like Google Drive, Dropbox, etc. and have it synced across multiple devices.

Functionality

It keeps all encrypted data and master encryption key in a dedicated directory with files structured on inodes (with meta info), files for binary content and directories with files/directories entries. All data, metadata and also filenames are encrypted. For new files it generates inode number randomly in u64 space so it reduces the chance of conflicts when used offline and synced later.

Password is collected from CLI and it's saved in OS keyring while app is running. This is because of safety reasons we clear the password from memory on inactivity and we reload it again from keyring just when needed.

Master encryption key is also encrypted with another key derived from the password. This gives the ability to change the password without re-encrypting all data, we just re-encrypt the master key.

Stack

• it's fully async built upon tokio and fuse3
• ring for encryption and argon2 for key derivation function (creating key used to encrypt master encryption key from password)
• rand_chacha for random generators
• secrecy for keeping pass and encryption keys safe in memory and zeroing them when not used. It keeps encryption keys in memory only while being used and when not active it will release and zeroing them from memory
• password can be saved in OS keyring using keyring
• tracing for logs

Usage

You can use it as a command line tool to mount an encrypted file system, or directly using the library to build your own binary (for library, you can follow the documentation).

Command Line Tool

Dependencies

To use the encrypted file system, you need to have FUSE installed on your system. You can install it by running the following command (or based on your distribution).

Arch

sudo pacman -Syu && sudo pacman -S fuse3

Ubuntu

sudo apt-get update && sudo apt-get -y install fuse3

Install from AUR

You can install the encrypted file system binary using the following command

yay -Syu && yay -S rencfs

Install with cargo

You can install the encrypted file system binary using the following command

cargo install rencfs

A basic example of how to use the encrypted file system is shown below

rencfs mount --mount-point MOUNT_POINT --data-dir DATA_DIR

• MOUNT_POINT act as a client, and mount FUSE at given path
• DATA_DIR where to store the encrypted data with the sync provider. But it needs to be on the same filesystem as the data-dir

It will prompt you to enter a password to encrypt/decrypt the data.

Change Password

The master encryption key is stored in a file and encrypted with a key derived from the password. This offers the possibility to change the password without needing to re-encrypt the whole data. This is done by decrypting the master key with the old password and re-encrypting it with the new password.

To change the password, you can run the following command

rencfs change-password --data-dir DATA_DIR 

DATA_DIR where the encrypted data is stored

It will prompt you to enter the old password and then the new password.

Encryption info

You can specify the encryption algorithm adding this argument to the command line

--cipher CIPHER ...

Where CIPHER is the encryption algorithm. You can check the available ciphers with rencfs --help.
Default value is ChaCha20Poly1305.

Log level

You can specify the log level adding the --log-level argument to the command line. Possible values: TRACE, DEBUG, INFO (default), WARN, ERROR.

rencfs --log-level LEVEL ...

Start it in docker

Get the image

docker pull xorio42/rencfs

Start a container to set up mount in it

docker run -it --device /dev/fuse --cap-add SYS_ADMIN --security-opt apparmor:unconfined xorio42/rencfs:latest /bin/sh

In the container create mount and data directories

mkdir fsmnt && mkdir fsdata

Start rencfs

rencfs --mount-point fsmnt --data-dir fsdata

Enter a password for encryption.

Get the container ID

docker ps

In another terminal attach to running container with the above ID

docker exec -it <ID> /bin/sh

From here you can play with it by creating files in fsmnt directory

cd fsmnt
mkdir 1
ls
echo "test" > 1/test
cat 1/test

Building from source

Getting the sources

git clone git@github.com:radumarias/rencfs.git

Dependencies

Rust

To build from source, you need to have Rust installed, you can see more details on how to install it here.

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Accordingly, it is customary for Rust developers to include this directory in their PATH environment variable. During installation rustup will attempt to configure the PATH. Because of differences between platforms, command shells, and bugs in rustup, the modifications to PATH may not take effect until the console is restarted, or the user is logged out, or it may not succeed at all.

If, after installation, running rustc --version in the console fails, this is the most likely reason. In that case please add it to the PATH manually.

Other dependencies

Also, these deps are required (or based on your distribution):

Arch

sudo pacman -Syu && sudo pacman -S fuse3 base-devel

Ubuntu

sudo apt-get update && sudo apt-get install fuse3 build-essential

Build for debug

cargo build

Build release

cargo build --release

Run

cargo run -- --mount-point MOUNT_POINT --data-dir DATA_DIR

Developing inside a Container

See here how to configure for VsCode
And here for RustRover

You can use the .devcontainer directory from the project to start a container with all the necessary tools to build and run the app.

Future

• Plan is to implement it also on macOS and Windows
• A systemd service is being worked on rencfs-daemon
• A GUI is on the way rencfs_desktop
• Mobile apps for Android and iOS are on the way

Contribution

Feel free to fork it, change and use it in any way that you want. If you build something interesting and feel like sharing pull requests are always appreciated.

Limitations

• Aes256Gcm cipher can save files up to 64GB. This is because of the 32-bit counter used in the GCM mode. For more details see here and here
• ChaCha20Poly1305 cipher can save files up to 256GB, it uses a 64-bit counter. See more details here

Security

• Safety on process kill (or crash): all writes to encrypted content is done in a tmp file and then using mv to move to destination. the mv operation is atomic as it's using rename() which is atomic as per specs, see here That specification requires that the action of the function be atomic.
• Phantom reads: reading older content from a file, this is not possible. While writing, data is kept in a buffer and tmp file and on releasing the file handle we write the new content to the file (as per above the tmp file is moved into place with mv). After that we reset all opened readers so any reads after that will pick up the new content
  One problem that may occur is if we do a truncate we change the content of the file but the process is killed before we write the metadata with the new filesize. In this case next time we mount the system we are still seeing the old filesize but the content of the file could be bigger, and we read until the old size offset, se we would not pick up the new zeros bytes written on truncating by increasing the size. If content is smaller the read would stop and end-of-file of the actual content so this would not be such a big issue
• What kind of metadata does it leak: close to none. The filename, actual file size and other file attrs (times, permissions, other flags) are kept encrypted. What it could possible leak is the following
  • If a directory has children we keep those children in a directory with name as inode number with encrypted names of children as files in it. So we could see how many children a directory has, but we can't identify that actual directory name, we can just see it's inode number (internal representation like an id for each file) and we cannot see the actual filenames of directory or children. Also we cannot identify which file content correspond to a directory child
  • Each file content is saved in a separate file so we could see the size of the encrypted content, but not the actual filesize
  • We can also see the last time the file was accessed
• It's always recommended to use encrypted disks for at least your sensitive data, this project is not a replacement for that
• In order to reduce the risk of encryption key to be exposed from memory it's recommended to disable mem dumps on the OS level. Please see here how to do it on Linux
• Cold boot attacks: in order to reduce the risk of this we keep the encryption key in memory just as long as we really need it to encrypt/decrypt data and we are zeroing it after that. We also remove it from memory after a period of inactivity
• Please note that this project is not audited by any security expert. It's built with security in mind and tries to follow all the best practices, but it's not guaranteed to be secure
• **Also please backup your data, the project is still in development and there might be bugs that can lead to data loss **

Considerations

• Please note, this project doesn't try to reinvent the wheel or be better than already proven implementations
• This project doesn't want to be a replacement in any way of already proven file encryption solutions. If you really want close to bullet proof solutions than maybe this is not the ideal one for you. But is trying to offer a simple use of an ecryption solution that should be used taking into consideration all the security concerns from above
• It started as a learning project of Rust programming language and I feel like keep building more on it
• It's a fairly simple and standard implementation that tries to respect all security standards, use safe libs and ciphers in the implementation so that it can be extended from this. Indeed it doesn't have the maturity yet to "fight" other well known implementations but it can be a project from which others can learn or build upon or why not for some to actually use it keeping in mind all the above