Class: TTTLS13::Ech

Inherits:
Object
  • Object
show all
Defined in:
lib/tttls1.3/ech.rb

Overview

rubocop: disable Metrics/ClassLength

Class Method Summary collapse

Class Method Details

.aead_id2overhead_len(aead_id) ⇒ Object 



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# File 'lib/tttls1.3/ech.rb', line 332

def self.aead_id2overhead_len(aead_id)
  case aead_id
  when HPKE::AES_128_GCM, HPKE::CHACHA20_POLY1305
    16
  when HPKE::AES_256_GCM
    32
  end
end

.encode_ch_inner(inner, maximum_name_length, replaced) ⇒ String

Returns EncodedClientHelloInner.

Parameters:

Returns:

  • (String) —

    EncodedClientHelloInner



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# File 'lib/tttls1.3/ech.rb', line 158

def self.encode_ch_inner(inner, maximum_name_length, replaced)
  encoded = Message::ClientHello.new(
    legacy_version: inner.legacy_version,
    random: inner.random,
    legacy_session_id: '',
    cipher_suites: inner.cipher_suites,
    legacy_compression_methods: inner.legacy_compression_methods,
    extensions: replaced
  )
  server_name_length = \
    replaced[Message::ExtensionType::SERVER_NAME].server_name.length

  padding_encoded_ch_inner(
    # which does not include the Handshake structure's four byte header.
    encoded.serialize[4..],
    server_name_length,
    maximum_name_length
  )
end

.encrypted_ech_config(ech_config, hpke_cipher_suite_selector) ⇒ TTTLS13::EchState or nil, String or nil

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Parameters:

  • ech_config (ECHConfig)
  • hpke_cipher_suite_selector (Method)

Returns:



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# File 'lib/tttls1.3/ech.rb', line 77

def self.encrypted_ech_config(ech_config, hpke_cipher_suite_selector)
  public_name = ech_config.echconfig_contents.public_name
  key_config = ech_config.echconfig_contents.key_config
  public_key = key_config.public_key.opaque
  kem_id = key_config&.kem_id&.uint16
  config_id = key_config.config_id
  cipher_suite = hpke_cipher_suite_selector.call(key_config)
  aead_cipher = cipher_suite&.aead_id&.uint16
  return [nil, nil, nil] \
    if [kem_id, aead_cipher].any?(&:nil?)

  kem_curve, hash = kem_id2dhkem(kem_id)
  pkr = kem_curve&.new(hash)&.deserialize_public_key(public_key)
  return [nil, nil, nil] if pkr.nil?

  hpke = HPKE.new(kem_id, hash, aead_cipher)
  base_s = hpke.setup_base_s(pkr, "tls ech\x00" + ech_config.encode)
  enc = base_s[:enc]
  ctx = base_s[:context_s]
  ech_secret = base_s[:shared_secret]
  mnl = ech_config.echconfig_contents.maximum_name_length
  ech_state = EchState.new(
    mnl,
    config_id,
    cipher_suite,
    public_name,
    ctx
  )

  [ech_state, enc, ech_secret]
end

.kem_id2dhkem(kem_id) ⇒ Object 



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# File 'lib/tttls1.3/ech.rb', line 317

def self.kem_id2dhkem(kem_id)
  case kem_id
  when HPKE::DHKEM_P256_HKDF_SHA256
    [HPKE::DHKEM::EC::P_256, HPKE::HKDF_SHA256]
  when HPKE::DHKEM_P384_HKDF_SHA384
    [HPKE::DHKEM::EC::P_384, HPKE::HKDF_SHA384]
  when HPKE::DHKEM_P521_HKDF_SHA512
    [HPKE::DHKEM::EC::P_521, HPKE::HKDF_SHA512]
  when HPKE::DHKEM_X25519_HKDF_SHA256
    [HPKE::DHKEM::X25519, HPKE::HKDF_SHA256]
  when HPKE::DHKEM_X448_HKDF_SHA512
    [HPKE::DHKEM::X448, HPKE::HKDF_SHA512]
  end
end

.new_ch_outer(aad, cipher_suite, config_id, enc, payload) ⇒ TTTLS13::Message::ClientHello

Parameters:

Returns:



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# File 'lib/tttls1.3/ech.rb', line 239

def self.new_ch_outer(aad, cipher_suite, config_id, enc, payload)
  outer_ech = Message::Extension::ECHClientHello.new_outer(
    cipher_suite:,
    config_id:,
    enc:,
    payload:
  )
  Message::ClientHello.new(
    legacy_version: aad.legacy_version,
    random: aad.random,
    legacy_session_id: aad.legacy_session_id,
    cipher_suites: aad.cipher_suites,
    legacy_compression_methods: aad.legacy_compression_methods,
    extensions: aad.extensions.merge(
      Message::ExtensionType::ENCRYPTED_CLIENT_HELLO => outer_ech
    )
  )
end

.new_ch_outer_aad(inner, cipher_suite, config_id, enc, payload_len, server_name) ⇒ TTTLS13::Message::ClientHello

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Parameters:

Returns:



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# File 'lib/tttls1.3/ech.rb', line 206

def self.new_ch_outer_aad(inner,
                          cipher_suite,
                          config_id,
                          enc,
                          payload_len,
                          server_name)
  aad_ech = Message::Extension::ECHClientHello.new_outer(
    cipher_suite:,
    config_id:,
    enc:,
    payload: payload_len.zeros
  )
  Message::ClientHello.new(
    legacy_version: inner.legacy_version,
    legacy_session_id: inner.legacy_session_id,
    cipher_suites: inner.cipher_suites,
    legacy_compression_methods: inner.legacy_compression_methods,
    extensions: inner.extensions.merge(
      Message::ExtensionType::ENCRYPTED_CLIENT_HELLO => aad_ech,
      Message::ExtensionType::SERVER_NAME => \
        Message::Extension::ServerName.new(server_name)
    )
  )
end

.new_grease_ech ⇒ Message::Extension::ECHClientHello

Returns:



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# File 'lib/tttls1.3/ech.rb', line 259

def self.new_grease_ech
  # https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-17#name-compliance-requirements
  cipher_suite = HpkeSymmetricCipherSuite.new(
    HpkeSymmetricCipherSuite::HpkeKdfId.new(
      HPKE::HKDF_SHA256
    ),
    HpkeSymmetricCipherSuite::HpkeAeadId.new(
      HPKE::AES_128_GCM
    )
  )
  # Set the enc field to a randomly-generated valid encapsulated public key
  # output by the HPKE KEM.
  #
  # https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-17#section-6.2-2.3.1
  public_key = OpenSSL::PKey.read(
    OpenSSL::PKey.generate_key('X25519').public_to_pem
  )
  hpke = HPKE.new(HPKE::DHKEM_X25519_HKDF_SHA256, HPKE::HKDF_SHA256, HPKE::AES_128_GCM)
  enc = hpke.setup_base_s(public_key, '')[:enc]
  # Set the payload field to a randomly-generated string of L+C bytes, where
  # C is the ciphertext expansion of the selected AEAD scheme and L is the
  # size of the EncodedClientHelloInner the client would compute when
  # offering ECH, padded according to Section 6.1.3.
  #
  # https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-17#section-6.2-2.4.1
  payload_len = placeholder_encoded_ch_inner_len \
                + aead_id2overhead_len(HPKE::AES_128_GCM)

  Message::Extension::ECHClientHello.new_outer(
    cipher_suite:,
    config_id: Convert.bin2i(OpenSSL::Random.random_bytes(1)),
    enc:,
    payload: OpenSSL::Random.random_bytes(payload_len)
  )
end

.new_greased_ch(inner, ech) ⇒ TTTLS13::Message::ClientHello

Parameters:

Returns:



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# File 'lib/tttls1.3/ech.rb', line 304

def self.new_greased_ch(inner, ech)
  Message::ClientHello.new(
    legacy_version: inner.legacy_version,
    random: inner.random,
    legacy_session_id: inner.legacy_session_id,
    cipher_suites: inner.cipher_suites,
    legacy_compression_methods: inner.legacy_compression_methods,
    extensions: inner.extensions.merge(
      Message::ExtensionType::ENCRYPTED_CLIENT_HELLO => ech
    )
  )
end

.offer_ech(inner, ech_config, hpke_cipher_suite_selector) ⇒ TTTLS13::Message::ClientHello, ...

rubocop: disable Metrics/AbcSize

Parameters:

Returns:



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# File 'lib/tttls1.3/ech.rb', line 26

def self.offer_ech(inner, ech_config, hpke_cipher_suite_selector)
  return [new_greased_ch(inner, new_grease_ech), nil, nil, nil] \
    if ech_config.nil? ||
       !SUPPORTED_ECHCONFIG_VERSIONS.include?(ech_config.version)

  # Encrypted ClientHello Configuration
  ech_state, enc, ech_secret = encrypted_ech_config(
    ech_config,
    hpke_cipher_suite_selector
  )
  return [new_greased_ch(inner, new_grease_ech), nil, nil, nil] \
    if ech_state.nil? || enc.nil?

  # for ech_outer_extensions
  replaced = \
    inner.extensions.remove_and_replace!(DEFAULT_ECH_OUTER_EXTENSIONS)

  # Encoding the ClientHelloInner
  encoded = encode_ch_inner(inner, ech_state.maximum_name_length, replaced)
  overhead_len = aead_id2overhead_len(ech_state.cipher_suite.aead_id.uint16)

  # Authenticating the ClientHelloOuter
  aad = new_ch_outer_aad(
    inner,
    ech_state.cipher_suite,
    ech_state.config_id,
    enc,
    encoded.length + overhead_len,
    ech_state.public_name
  )

  outer = new_ch_outer(
    aad,
    ech_state.cipher_suite,
    ech_state.config_id,
    enc,
    # which does not include the Handshake structure's four byte header.
    ech_state.ctx.seal(aad.serialize[4..], encoded)
  )

  [outer, inner, ech_state, ech_secret]
end

.offer_new_ech(inner, ech_state) ⇒ TTTLS13::Message::ClientHello

Parameters:

Returns:



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# File 'lib/tttls1.3/ech.rb', line 115

def self.offer_new_ech(inner, ech_state)
  # for ech_outer_extensions
  replaced = \
    inner.extensions.remove_and_replace!(DEFAULT_ECH_OUTER_EXTENSIONS)

  # Encoding the ClientHelloInner
  encoded = encode_ch_inner(inner, ech_state.maximum_name_length, replaced)
  overhead_len = \
    aead_id2overhead_len(ech_state.cipher_suite.aead_id.uint16)

  # It encrypts EncodedClientHelloInner as described in Section 6.1.1, using
  # the second partial ClientHelloOuterAAD, to obtain a second
  # ClientHelloOuter. It reuses the original HPKE encryption context
  # computed in Section 6.1 and uses the empty string for enc.
  #
  # https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni-17#section-6.1.5-4.4.1
  aad = new_ch_outer_aad(
    inner,
    ech_state.cipher_suite,
    ech_state.config_id,
    '',
    encoded.length + overhead_len,
    ech_state.public_name
  )

  # Authenticating the ClientHelloOuter
  outer = new_ch_outer(
    aad,
    ech_state.cipher_suite,
    ech_state.config_id,
    '',
    # which does not include the Handshake structure's four byte header.
    ech_state.ctx.seal(aad.serialize[4..], encoded)
  )

  [outer, inner]
end

.padding_encoded_ch_inner(s, server_name_length, maximum_name_length) ⇒ String

Parameters:

  • s (String)
  • server_name_length (Integer)
  • maximum_name_length (Integer)

Returns:

  • (String) 


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# File 'lib/tttls1.3/ech.rb', line 183

def self.padding_encoded_ch_inner(s,
                                  server_name_length,
                                  maximum_name_length)
  padding_len =
    if server_name_length.positive?
      [maximum_name_length - server_name_length, 0].max
    else
      9 + maximum_name_length
    end

  padding_len = 31 - ((s.length + padding_len - 1) % 32)
  s + padding_len.zeros
end

.placeholder_encoded_ch_inner_len ⇒ Integer

Returns:

  • (Integer) 


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# File 'lib/tttls1.3/ech.rb', line 296

def self.placeholder_encoded_ch_inner_len
  480
end