hpke-rb

Hybrid Public Key Encryption (HPKE; RFC 9180) in Ruby

This is still in very early development, so:

• APIs are subject to change
  • Especially the instantation interface of KEM and HPKE suite
• This is tested against test vectors supplied by the authors of the RFC, but is not formally audited for security. Please be aware of this when using in production.

Supports all modes, KEMs, AEAD functions in RFC 9180.

• HPKE Modes
  • Base
  • PSK
  • Auth
  • AuthPSK
• Key Encapsulation Mechanisms (KEMs)
  • DHKEM(P-256, HKDF-SHA256)
  • DHKEM(P-384, HKDF-SHA384)
  • DHKEM(P-521, HKDF-SHA512)
  • DHKEM(X25519, HKDF-SHA256)
  • DHKEM(X448, HKDF-SHA512)
• Key Derivation Functions (KDFs)
  • HKDF-SHA256
  • HKDF-SHA384
  • HKDF-SHA512
• AEAD Functions
  • AES-128-GCM
  • AES-256-GCM
  • ChaCha20-Poly1305
  • Export Only

• OpenSSL 3.0 or higher
  • This is due to the changes in instantiation of public/private key pairs from OpenSSL 1.1 series to OpenSSL 3.0 series
• Ruby 3.1 or higher
  • Ruby 3.1 comes with OpenSSL 3.0 support

Install the gem and add to the application's Gemfile by executing:

$ bundle add hpke

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install hpke

(example shows Base mode)

# instantiate HPKE suite
# first 2 parameters specify the curve and hash to be used in the KEM,
# third parameter specifies the hash to be used in the KDF (of HPKE suite),
# fourth parameter specifies the AEAD function

# we will generate a different instance just for demonstration to show that nothing secret is stored in the HPKE suite instance
hpke_s = HPKE.new(:x25519, :sha256, :sha256, :aes_128_gcm)
hpke_r = HPKE.new(:x25519, :sha256, :sha256, :aes_128_gcm)

# get a OpenSSL::PKey::PKey instance by either generating a key or loading a key from a PEM
# see https://ruby-doc.org/3.2.2/exts/openssl/OpenSSL/PKey/PKey.html
# on the sender's end
sender_key_pair = OpenSSL::PKey.generate_key('X25519')
receiver_key_pair = OpenSSL::PKey.generate_key('X25519')

# Sender setup
# Sender knows the receiver's public key (in PEM format, in most cases), so load that into a PKey
receiver_public_key = OpenSSL::PKey.read(receiver_key_pair.public_to_pem)
encap_result = hpke_s.setup_base_s(receiver_public_key, 'info')
# This returns a hash where :enc key contains the key encapsulation,
# and :context_s contains a HPKE::ContextS instance, which is used for encryption later on.
context_s = encap_result[:context_s]
# Note that :enc contains raw bytes, so when passing to the receiver, it is advised to pass the encapsulation using Base64-encoded values
enc_base64 = Base64.encode64(encap_result[:enc])

# Then on the receiver's end
# decode the encapsulated value
enc = Base64.decode64(enc_base64)
# then use that value to generate a HPKE::ContextR instance to use for decryption
context_r = hpke_r.setup_base_r(enc, receiver_key_pair, 'info')

# sender encrypts a message
# note that the "sequence number" is incremented each time `seal` and `open` is used
ciphertext = context_s.seal('authentication_associated_data', 'plaintext')
# this is also in raw bytes, so when sending, encoding with Base64 is advised

# then receiver decrypts the ciphertext
context_r.open('authentication_associated_data', ciphertext)

• Curve names (parameter 1)
  • :p_256, :p_384, :p_521, :x25519, :x448
    • Note: :p_256 corresponds to prime256v1, :p_384 corresponds to secp384r1, and :p_521 corresponds to secp521r1 in OpenSSL
• Hash names (parameter 2 and 3)
  • :sha256, :sha384, :sha512
• AEAD function names (parameter 4)
  • :aes_128_gcm, :aes_256_gcm, :chacha20_poly1305, :export_only

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/sylph01/hpke-rb.

The gem is available as open source under the terms of the MIT License.