XChaCha20-Poly1305 support

[rfjakob]

gocryptfs has added XChaCha20-Poly1305 for file content encryption. It's already in master and I want to release it as gocryptfs v2.2.

It would be nice to have an independent implementation before I release this to the unsuspecting public :)

• The feature flag is called XChaCha20Poly1305
• HKDF context is here https://github.com/rfjakob/gocryptfs/blob/master/internal/cryptocore/hkdf.go#L16
• Nonce is 24 bytes instead of 16, doc is here: https://github.com/rfjakob/gocryptfs/blob/master/Documentation/file-format.md
• Example filesystem is here: https://github.com/rfjakob/gocryptfs/tree/master/tests/example_filesystems/v2.2-xchacha

Everything else is the same as for AES-GCM and AES-SIV.

[slackner]

Hi Jakob,

Good job, very exciting to see support for some additional encryption algorithms. :+1: :tada:

I just implemented XChaCha suport in gocryptfs-inspect, and everything looks pretty good so far: https://github.com/slackner/gocryptfs-inspect/commit/39e6c69d757bc9b94350e7012829f68982cf8803

The code still needs a bit of cleanup before merging, but all tests pass, so no reason to delay the release of your new gocryptfs version :smile:

Best regards, Sebastian

[rfjakob]

Great, thank you!!