This is an implementation of XAES-256-GCM as proposed by Filippo Valsorda, for Ruby.

Resources:

• Original post by Filippo: https://words.filippo.io/dispatches/xaes-256-gcm/
• The XAES-256-GCM specification: https://github.com/C2SP/C2SP/blob/main/XAES-256-GCM.md
• Reference implementations for Go and OpenSSL: https://github.com/C2SP/C2SP/tree/main/XAES-256-GCM

Get from rubygems.org: https://rubygems.org/gems/xaes_256_gcm

require "xaes_256_gcm"

key = # assign to some key.
plaintext = "Hello XAES-256-GCM from Ruby"

xaes = Xaes256Gcm::Xaes256GcmCipher.new(key)

# Seal, or encrypt
ciphertext = xaes.seal(plaintext)

# Open, or decrypt
decrypted = xaes.open(ciphertext)

Optionally, AAD (additional authenticated data) can be passed as a 2nd argument to seal and open.

This implementation of XAES-256-GCM will generate secure nonce for you automatically when using seal and open. If low-level control over the nonce is required, encrypt and decrypt accept a nonce independently. It is recommended that the high-level seal and open that create a nonce for you is used unless strict control over the nonce is required.

The "simple" nonce managed APIs are not formally specified in by C2SP. Here we define them simply as

Encryption:

N = CSPRNG_bytes(24)
ciphertext = encrypt(N, plaintext, aad)
sealed = N || ciphertext

Decryption:

N = sealed[:24]
ciphertext = sealed[24:]
plaintext = decrypt(N, ciphertext, add)

Tests can be run with bin/bundle exec rspec