#encryption #ftp #directory #local #serve #scrypt #data

app x79d8

Serve encrypted files via local FTP

1 unstable release

0.2.0 Dec 14, 2020

#1236 in Filesystem

GPL-2.0-only

74KB
2K SLoC

x79d8

build

Portable directory encryption.

Encrypted files are stored on the host OS filesystem. Decrypted files are served via a local FTP service.

Features

  • Portable. Use FTP. Most systems support FTP.
  • Dynamic sized. Space usage grows or shrinks based on usage.
  • Industry encryption. AES256 for data encryption. scrypt for key derivation.

Installation

cargo install x79d8

Note: Follow instructions from the aesni crate to enable hardware acceleration. In short, you might need to set RUSTFLAGS to -C target-feature=+aes during installation.

Usage

Initializing a new directory

Initialize x79d8 configs in an empty directory:

x79d8 init

Serve the directory. This will prompt for a new password:

x79d8 serve

Upload files to ftp://127.0.0.2:2121. Press Ctrl+C to store the encrypted files on disk.

Serving an existing directory

Serve the directory. This will prompt for the password and will only serve the right content if the password is correct:

x79d8 serve

Encryption

x79d8 uses AES256-CFB to encrypt blocks. A block has an integer block_id, which is the file name on the host OS filesystem. The header of a block has a random 128-bit integer count. The IV used for encrypting that block is blake2s(key, count, block_id). The count will be changed whenever the block is written. If a block is deleted and re-added, its count will be re-initialized by the OS rng. The OS RNG must be secure to eliminate IV reuse in that case.

By default, a block is 1MB. Smaller files will be grouped into one block. Larger files are will span across multiple blocks. This behavior can be changed by the --block-size-kb option during init.

x79d8 uses scrypt to calculate the key from password. Its strength can be changed by the --scrypt-log-n option during init.

x79d8 assumes it's a local service and there are no untrusted traffic. For example, it does not use AEAD (authenticated encryption with associated data). Do not expose x79d8 features to untrusted network! Do not allow untrusted users to edit the encrypted files (in particular, they can replace a block to its previous version to trick an IV-reuse case, if the OS RNG is also insecure)!

Durability

x79d8 starts to write changes to disk after 5 seconds. It uses WAL to ensure data consistency.

Background

I've been looking for TrueCrypt alternatives since its discontinuation. I'd like the alternative to have dynamic space usage, is trustworthy (open-source, audited or simple enough to audit), and cross-platform. Unfortunately, it's not easy to find a good alternative. The RustCrypto libraries seem serious enough to DIY a solution, and libunftp simplifies the "cross-platform" part a lot.

x79d8 is only about 2k lines. The main encryption logic (enc.rs) is only about 160 lines.

Dependencies

~26–39MB
~715K SLoC