DroidFS

DroidFS is an alternative way to use encrypted overlay filesystems on Android that uses its own internal file explorer instead of mounting virtual volumes. It currently supports gocryptfs and CryFS (alpha).

Disclaimer

DroidFS is provided "as is", without any warranty of any kind. It shouldn't be considered as an absolute safe way to store files. DroidFS cannot protect you from screen recording apps, keyloggers, apk backdooring, compromised root accesses, memory dumps etc. Do not use this app with volumes containing sensitive data unless you know exactly what you are doing.

Unsafe features

DroidFS allows you to enable/disable unsafe features to fit your needs between security and comfort. It is strongly recommended to read the documentation of a feature before enabling it.

• Allow screenshots:

  Disable the secure flag of DroidFS activities. This will allow you to take screenshots from the app, but will also allow other apps to record the screen while using DroidFS. Note: apps with root access don't care about this flag: they can take screenshots or record the screen of any app without any permissions.

• Allow opening files with other applications *:

  Decrypt and open file using external apps. These apps could save and send the files thus opened.

• Allow exporting files:

  Decrypt and write file to disk (external storage). Any app with storage permissions could access exported files.

• Allow sharing files via the android share menu *:

  Decrypt and share file with other apps. These apps could save and send the files thus shared.

• Keep volume open when the app goes in background:

  Don't close the volume when you leave the app but keep running it in the background. Anyone going back to the activity could have access to the volume.

• Allow saving password hash using fingerprint:

  Generate an AES-256 GCM key in the Android Keystore (protected by fingerprint authentication), then use it to encrypt the volume password hash and store it to the DroidFS internal storage. This require Android v6.0+. If your device is not encrypted, extracting the encryption key with physical access may be possible.

* Features requiring temporary writing of the plain file to disk (DroidFS internal storage). This file could be read by apps with root access or by physical access if your device is not encrypted.

Download

You can download DroidFS from F-Droid or from the "Releases" section in this repository.

APKs available here are signed with my PGP key available on keyservers:

gpg --keyserver hkps://keyserver.ubuntu.com --recv-keys AFE384344A45E13A
Fingerprint: B64E FE86 CEE1 D054 F082 1711 AFE3 8434 4A45 E13A
Email: Hardcore Sushi <hardcore.sushi@disroot.org>

To verify APKs, save the PGP-signed message to a file and run gpg --verify <the file>. Don't install any APK if the verification fails !

If the signature is valid, you can compare the SHA256 checksums with:

sha256sum <APK file>

Don't install the APK if the checksums don't match!

F-Droid APKs should be signed with the F-Droid key. More details here.

Permissions

DroidFS need some permissions to work properly. Here is why:

• Read & write access to shared storage:

  Required for creating, opening and modifying volumes and for importing/exporting files to/from volumes.

• Biometric/Fingerprint hardware:

  Required to encrypt/decrypt password hashes using a fingerprint protected key.

• Camera:

  Needed to take photos & videos directly encrypted inside DroidFS. You can deny this permission if you don't want to use it.

• Record audio:

  Required if you want sound on video recorded with DroidFS.

Limitations

DroidFS works as a wrapper around modified versions of the original encrypted container implementations (libgocryptfs and libcryfs). These programs were designed to run on standard x86 Linux systems: they access the underlying file system with file paths and syscalls. However, on Android, you can't access files from other applications using file paths. Instead, one has to use the ContentProvider API. Obviously, neither Gocryptfs nor CryFS support this API. As a result, DroidFS cannot open volumes provided by other applications (such as cloud storage clients), nor can it allow other applications to access encrypted volumes once opened.

Due to Android's storage restrictions, encrypted volumes located on SD cards must be placed under /Android/data/sushi.hardcore.droidfs/ if you want DroidFS to be able to modify them.

Building from source

You can follow the instructions in BUILD.md to build DroidFS from source.

Third party code

Thanks to these open source projects that DroidFS uses:

Modified code:

• Encrypted filesystems (to protect your data):
  • libgocryptfs (forked from gocryptfs)
  • libcryfs (forked from CryFS)
• libpdfviewer (forked from PdfViewer) to open PDF files
• DoubleTapPlayerView to add double-click controls to the video player

Borrowed code:

• MaterialFiles for Kotlin natural sorting implementation

Libraries:

• Glide to display pictures
• ExoPlayer to play media files