libgocryptfs/README.md

An encrypted overlay filesystem written in Go.

gocryptfs is built on top the excellent go-fuse FUSE library and its LoopbackFileSystem API.

This project was inspired by EncFS and strives to fix its security issues while providing good performance. For details on the security of gocryptfs see the SECURITY.md design document.

Current Status

Beta. You are advised to keep a backup of your data outside of gocryptfs, in addition to storing the master key in a safe place (the master key is printed when mounting).

Only Linux is supported at the moment. Help wanted for a Mac OS X port.

Testing

gocryptfs comes with is own test suite that is constantly expanded as features are added. Run it using ./test.bash. It takes about 30 seconds and requires FUSE as it mounts several test filesystems.

In addition, I have ported xfstests to FUSE, the result is the fuse-xfstests project. gocryptfs passes the "generic" tests with one exception, results: XFSTESTS.md

A lot of work has gone into this. The testing has found bugs in gocryptfs as well as in go-fuse.

The one exception is generic/035, see go-fuse issue 55 for details. While this is a POSIX violation, I do not see any real-world impact.

Install

$ go get github.com/rfjakob/gocryptfs

Use

Quickstart:

$ mkdir cipher plain
$ $GOPATH/bin/gocryptfs --init cipher
  [...]
$ $GOPATH/bin/gocryptfs cipher plain
  [...]
$ echo test > plain/test.txt
$ ls -l cipher
  total 8
  -rw-rw-r--. 1 user  user   33  7. Okt 23:23 0ao8Hyyf1A-A88sfNvkUxA==
  -rw-rw-r--. 1 user  user  233  7. Okt 23:23 gocryptfs.conf
$ fusermount -u plain

See MANPAGE.md for a description of available options. If you already have gocryptfs installed, run ./MANPAGE-render.bash to bring up the rendered manpage in the pager (requires pandoc).

Storage Overhead

• Empty files take 0 bytes on disk
• 18 byte file header for non-empty files (2 bytes version, 16 bytes random file id)
• 28 bytes of storage overhead per 4kB block (12 byte nonce, 16 bytes auth tag)

Performance

gocryptfs uses openssl through spacemonkeygo/openssl for a 3x speedup compared to Go's builtin AES-GCM implementation (see go-vs-openssl.md for details).

Run ./benchmark.bash to run the benchmarks.

The output should look like this:

./benchmark.bash
gocryptfs v0.3.1-30-gd69e0df-dirty; on-disk format 2
PASS
BenchmarkStreamWrite-2	     100	  12246070 ns/op	  85.63 MB/s
BenchmarkStreamRead-2 	     200	   9125990 ns/op	 114.90 MB/s
BenchmarkCreate0B-2   	   10000	    101284 ns/op
BenchmarkCreate1B-2   	   10000	    178356 ns/op	   0.01 MB/s
BenchmarkCreate100B-2 	    5000	    361014 ns/op	   0.28 MB/s
BenchmarkCreate4kB-2  	    5000	    375035 ns/op	  10.92 MB/s
BenchmarkCreate10kB-2 	    3000	    491071 ns/op	  20.85 MB/s
ok  	github.com/rfjakob/gocryptfs/integration_tests	17.216s

Changelog

v0.7

• Extend GCM IV size to 128 bit from Go's default of 96 bit
• This pushes back the birthday bound to make IV collisions virtually impossible
• This is a forwards-compatible change. gocryptfs v0.7 can mount filesystems created by earlier versions but not the other way round.
• New command-line option:
• -gcmiv128: Use 128-bit GCM IVs (default true)

v0.6

• Wide-block filename encryption using EME + DirIV
• EME (ECB-Mix-ECB) provides even better security than CBC as it fixes the prefix leak. The used Go EME implementation is https://github.com/rfjakob/eme which is, as far as I know, the first implementation of EME in Go.
• This is a forwards-compatible change. gocryptfs v0.6 can mount filesystems created by earlier versions but not the other way round.
• New command-line option:
• -emenames: Enable EME filename encryption (default true)

v0.5

• Stronger filename encryption: DirIV
• Each directory gets a random 128 bit file name IV on creation, stored in gocryptfs.diriv
• This makes it impossible to identify identically-named files across directories
• A single-entry IV cache brings the performance cost of DirIV close to zero for common operations (see performance.txt)
• This is a forwards-compatible change. gocryptfs v0.5 can mount filesystems created by earlier versions but not the other way round.
• New command-line option:
• -diriv: Use the new per-directory IV file name encryption (default true)
• -scryptn: allows to set the scrypt cost parameter N. This option can be used for faster mounting at the cost of lower brute-force resistance. It was mainly added to speed up the automated tests.

v0.4

• New command-line options:
• -plaintextnames: disables filename encryption, added on user request
• -extpass: calls an external program for prompting for the password
• -config: allows to specify a custom gocryptfs.conf path
• Add FeatureFlags gocryptfs.conf paramter
• This is a config format change, hence the on-disk format is incremented
• Used for ext4-style filesystem feature flags. This should help avoid future format changes. The first user is -plaintextnames.
• On-disk format 2

v0.3

• Add a random 128 bit file header to authenticate file->block ownership
• This is an on-disk-format change
• On-disk format 1

v0.2

• Replace bash daemonization wrapper with native Go implementation
• Better user feedback on mount failures

v0.1

• First release
• On-disk format 0

See https://github.com/rfjakob/gocryptfs/tags for the release dates and associated git tags.