securefs

securefs is a filesystem in userspace (FUSE) with transparent encryption (when writing) and decryption (when reading).

securefs mounts a regular directory onto a mount point. The mount point appears as a regular filesystem, where one can read/write/create files, directories and symbolic links. The underlying directory will be automatically updated to contain the encrypted and authenticated contents.

Motivation

From sensitive financial records to personal diaries and collection of guilty pleasures, we all have something to keep private from prying eyes. Especially when we store our files in the cloud, the company and the NSA may well get their hands upon it. The best protection we can afford ourselves is cryptography, the discipline developed by mathematicians and military originally to keep the national secrets.

Security, however, is often at odds with convenience, and people easily grow tired of the hassle and revert to no protection at all. Consider the case of protecting our files either locally or in the cloud: we have to encrypt the files before committing to the cloud and decrypt it every time we need to read and write. Worse still, such actions leave unencrypted traces on our hard drive. If we store data in the cloud, another issue arise: manual encryption and decryption prevent files from being synced efficiently.

securefs is intended to make the experience as smooth as possible so that the security and convenience do not conflict. After mounting the virtual filesystem, everything just works™.

Comparison

There are already many encrypting filesystem in widespread use. Some notable ones are TrueCrypt, FileVault, BitLocker, eCryptFS, encfs, cryfs, rclone and gocryptfs. securefs differs from them in that it is the only one with all of the following features:

• Authenticated encryption (hence secure against chosen ciphertext attacks)
• Probabilistic encryption (hence provides semantical security)
• Supported on all major platforms (Mac, Linux, BSDs and Windows)
• Efficient cloud synchronization (not a single preallocated file as container)
• Full 255 bytes long file name components.
• (Optional) File size obfuscation by random padding.
• (Optional) Case insensitive and case preserving filesystem (matching the default behavior of NTFS).
• (Optional) Unicode normalization agnostic filesystem (matching the default behavior of APFS/HFS+)

Install

Dependencies

On Windows, we need to separately install WinFsp and VC++ redistributable.

On Linux, we need to install libfuse-dev/fuse-devel package.

On FreeBSD, we need to run pkg install fusefs-libs.

On macOS, we need to install MacFUSE.

Binary packages

Download from the Release page.

Build from source

First you need to install vcpkg. Then run python3 build.py --enable_unit_test.

Package managers

macOS

Use homebrew.

brew install netheril96/fuse/securefs-mac

Basic usage

It is recommended to disable or encrypt the swap and hibernation file. Otherwise plaintext and keys stored in the main memory may be written to disk by the OS at any time.

Examples:

# Help commands
securefs --help
securefs m --help
securefs c --help
# Creation
securefs create ~/Secret # Default parameters
securefs create ~/Secret --keyfile ./mykey # Use keyfile instead of password
securefs c ~/Secret --max-padding 65535 # Randomly pad each file with at most 65535 bytes to obfuscate its size
securefs c ~/Secret --format full # Full mode. See below for the meaning.
securefs c ~/Secret --format full --case insensitive # Like NTFS
securefs c ~/Secret --format full --uninorm insensitive # Like APFS
# Mounting
securefs mount ~/Secret ~/Mount # press Ctrl-C to unmount
securefs mount ~/Secret ~/Mount --keyfile ./mykey # press Ctrl-C to unmount
# Mount in the background (no-op on Windows). Use `umount` to unmount.
securefs m -b ~/Secret ~/Mount --log ~/securefs.thismaycontainsensitiveinformation.log
securefs m --plain-text-names ~/Secret ~/Mount # Do not encrypt the filenames
securefs m ~/Secret Z: # Windows only
# Change password
securefs chpass ~/Secret

See the full command line options.

GUI

SiriKali is a GUI frontend for securefs (and several other filesystems).

Note: this is informational only. The author of securefs has never tried SiriKali or vetted its code.

Lite and full mode

There are two categories of filesystem format.

The lite format simply encrypts filenames and file contents separately, similar to how encfs operates, although with more security.

The full format maps files, directory and symlinks in the virtual filesystem all to regular files in the underlying filesystem. The directory structure is flattened and recorded as B-trees in files.

The lite format is the default as it is much faster and features easier conflict resolution, especially when used with DropBox, Google Drive, etc. The full format, however, leaks fewer information about the filesystem hierarchy, runs relatively independent of the features of the underlying filesystem, and is in general more secure.

To request full format, which is no longer the default, run securefs create --format full.

Design and algorithms

See here.

Caveat

If you store securefs encrypted files on iCloud Drive, it might cause Spotlight Search on iOS to stop working. It is a bug in iOS, not in securefs.

To work around that bug, you can disable the indexing of Files app in Settings -> Siri & Suggestions.

Crash resistance

If securefs exits abnormally, or if the computer suddenly powers down, we have only the following guarantees (assuming the underlying filesystem isn't corrupted)

1. Files not being written will never be corrupted.
2. In lite format, the directory structure and file names will not be corrupted, unless the file name is a long name.
3. In full format, the directory structure and file names may be corrupted, but the files themselves can be recovered even in this case.