rencfs

[!WARNING]
This crate hasn’t been audited, it’s using ring crate which is a well-known audited library, so in principle at least the primitives should offer similar level of security.
This is still under development. Please do not use it with sensitive data for now, please wait for a stable release.
It’s mostly ideal for experimental and learning projects.

An encrypted file system written in Rust that is mounted with FUSE on Linux. It can be used to create encrypted directories.

You can then safely backup the encrypted directory to 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.

You can use it as CLI or as a library to build your custom FUSE implementation or other apps that works with encrypted data.

Key features

• Security using well-known audited AEAD cryptography primitives
• Data integrity, data is written with WAL to ensure integrity even on crash or power loss
• All metadata and content are encrypted
• Safe manage of credentials in memory with mlock(2), mprotect, zeroize and expiry
• Encryption key generated based on password
• Password saved in OS’s keyring
• Change password without re-encrypting all data
• Fast seek on both reads and writes
• Writes in parallel
• Exposed with FUSE
• Fully concurrent for all operations

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.
• The 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.
• Files are encrypted in chunks of 256KB, so when making a change, we just re-encrypt those chunks.
• Fast seek on read and write, so if you’re watching a movie, you can seek to any position, and that would be rapid. This is because we can seek to particular chunk.
• Encryption key is zeroized in mem on idle. Also, it’s mlocked while used to prevent being moved to swap. It’s also mprotected while not read.

In progress:

• ensure file integrity by saving each change to WAL, so on crash or power loss on next start we apply the pending changes. This makes the write operations atomic.
• multiple writes in parallel to the same file, ideal for torrent like applications

Stack

• it’s fully async built upon tokio and fuse3
• ring for encryption and argon2 for key derivation function (creating key used to encrypt the 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 in memory
• blake3 for hashing
• password saved in OS keyring using keyring
• tracing for logs

Usage

Give it a quick try with 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 --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

As a library

For the 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 the 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 passwd --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 ...

Use it in Rust

You can see more here

Build from source

Browser

You can compile it, run it, and give it a quick try in browser. After you start it from above

sudo apt-get update && sudo apt-get install fuse3
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
mkdir mnt && mkdir data
cargo run --release -- mount -m mnt -d data

Open another terminal

cd mnt
mkdir a && cd a
echo "test" > test.txt
cat test.txt

Locally

For now the FUSE (fuse3 crate) only works on Linux, so to start the project you will need to be on Linux. Instead, you can Develop inside a Container, which will start a local Linux container, the IDE will connect to it, you can build and start the app in there and also use terminal to test it.

Getting the sources

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

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.

Project is setup to use nightly toolchain in rust-toolchain.toml, on first build you will see it fetch the nightly.

cargo install cargo-aur
cargo install cargo-generate-rpm

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

Fedora

sudo dnf update && sudo dnf install fuse3 && dnf install @development-tools

Build for debug

cargo build

Build release

cargo build --release

Run

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

Dev settings

If you don’t want to be prompted for password, you can set this env var and run like this:

RENCFS_PASSWORD=PASS cargo run --release -- mount --mount-point MOUNT_POINT --data-dir DATA_DIR

For dev mode is recommended to run with DEBUG log level:

cargo run --release -- --log-level DEBUG mount --mount-point MOUNT_POINT --data-dir DATA_DIR

Build local RPM for Fedora

This is using cargo-generate-rpm

cargo install cargo-generate-rpm
cargo build --release
cargo generate-rpm

The generated RPM will be located here: target/generate-rpm.

Install and run local RPM

cd target/generate-rpm/
sudo dnf localinstall rencfs-xxx.x86_64.rpm

Developing inside a Container

See here how to configure for RustRover and for VsCode.

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

Minimum Supported Rust Version (MSRV)

The minimum supported version is 1.75.

Future

• Plan is to implement it also on macOS and Windows
• Systemd service is being worked on rencfs-daemon
• GUI is being worked on rencfs-desktop and rencfs-kotlin
• Mobile apps for Android and iOS are being worked on rencfs-kotlin

Performance

Aes256Gcm is slightly faster than ChaCha20Poly1305 by a factor of 1.28 on average. This is because of the hardware acceleration of AES on most CPUs via AES-NI. But where hardware acceleration is not available ChaCha20Poly1305 is faster. Also ChaChaPoly1305 is better at SIMD.

Cipher comparison

AES-GCM vs. ChaCha20-Poly1305

• If you have hardware acceleration (e.g. AES-NI), then AES-GCM provides better performance. On my benchmarks, it was faster by a factor of 1.28 on average.
  If you do not have a hardware acceleration, AES-GCM is either slower than ChaCha20-Poly1305, or it leaks your encryption keys in cache timing.
• AES-GCM can target multiple security levels (128-bit, 192-bit, 256-bit), whereas ChaCha20-Poly1305 is only defined at the 256-bit security level.
• Nonce size:
  • AES-GCM: Varies, but the standard is 96 bits (12 bytes). If you supply a longer nonce, this gets hashed down to 16 bytes.
  • ChaCha20-Poly1305: The standardized version uses 96-bit nonce (12 bytes), but the original used 64-bit nonce (8 bytes).
• Wear-out of a single (key, nonce) pair:
  • AES-GCM: Messages must be less than 2^32 – 2 blocks (a.k.a. 2^36 – 32 bytes, a.k.a. 2^39 – 256 bits), that’s roughly 64GB. This also makes the security analysis of AES-GCM with long nonces complicated, since the hashed nonce doesn’t start with the lower 4 bytes set to 00 00 00 02.
  • ChaCha20-Poly1305: ChaCha has an internal counter (32 bits in the standardized IETF variant, 64 bits in the original design). Max message length is 2^39 - 256 bits, about 256GB
• Neither algorithm is nonce misuse-resistant.
• ChaChaPoly1305 is better at SIMD

Conclusion

Both are good options. AES-GCM can be faster with hardware support, but pure-software implementations of ChaCha20-Poly1305 are almost always fast and constant-time.

Security

• Phantom reads: reading older content from a file, this is not possible. Data is written with WAL and periodically flushed to file. This ensures data integrity and maintains change order. 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. However, the content of the file could be bigger, and we read until the old size offset, so 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 possibly 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. However, we can’t identify that actual directory name, we can just see its 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 corresponds 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
• To reduce the risk of encryption key from being exposed from memory, it’s recommended to disable memory dumps on the OS level. Please see here how to do it on Linux
• Cold boot attacks: 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 this project was 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 back up 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 bulletproof solutions, then maybe this is not the ideal one for you. But is trying to offer a simple use of an encryption 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, correcly use secure and robust primitives 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

Contribute

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.

How to contribute

Please see CONTRIBUTING.md.