18F/identity-idp

# frozen_string_literal: true
 
class SessionEncryptor
  class SensitiveKeyError < StandardError; end
 
  class SensitiveValueError < StandardError; end
  CIPHERTEXT_HEADER = 'v3'
  MINIMUM_COMPRESS_LIMIT = 300
  SENSITIVE_KEYS = [
    'first_name', 'middle_name', 'last_name', 'address1', 'address2', 'city', 'state', 'zipcode',
    'zip_code', 'identity_doc_address1', 'identity_doc_address2', 'identity_doc_city',
    'identity_doc_zipcode', 'identity_doc_address_state', 'state_id_jurisdiction',
    'same_address_as_id', 'dob', 'phone_number', 'phone', 'ssn',
    'prev_address1', 'prev_address2', 'prev_city', 'prev_state', 'prev_zipcode', 'pii',
    'pii_from_doc', 'pii_from_user', 'password', 'personal_key', 'email', 'email_address',
    'unconfirmed_phone'
  ].to_set.freeze
  CIPHERTEXT_KEY = 't'
  COMPRESSED_KEY = 'c'
  VERSION_KEY = 'v'
 
  # 'idv/in_person' and 'idv' are used during the proofing process and can contain PII
  # personal keys are generated and stored in the session between requests, but are used
  # to decrypt PII bundles, so we treat them similarly to the PII itself.
  SENSITIVE_PATHS = [
    ['warden.user.user.session', 'idv/in_person'],
    ['warden.user.user.session', 'idv'],
    ['warden.user.user.session', 'personal_key'],
    ['warden.user.user.session', 'unconfirmed_phone'],
    ['flash', 'flashes', 'personal_key'],
    ['flash', 'flashes', 'email'],
    ['email'],
  ].freeze
 
  SENSITIVE_DEFAULT_FIELDS = Idp::Constants::MOCK_IDV_APPLICANT.slice(
    :last_name,
    :address1,
    :city,
    :dob,
    :state_id_expiration,
  ).values.freeze
  SENSITIVE_REGEX = %r{#{SENSITIVE_DEFAULT_FIELDS.join('|')}}i
 
  def load(value)
    payload = MessagePack.unpack(value)
    ciphertext = payload[CIPHERTEXT_KEY]
    compressed = payload[COMPRESSED_KEY]
    decrypted = outer_decrypt(ciphertext)
    decrypted = if compressed == 1
                  Zlib.gunzip(decrypted)
    else
      decrypted
    end
 
    session = JSON.parse(decrypted).with_indifferent_access
    kms_decrypt_sensitive_paths!(session)
 
    session
  end
 
  def dump(value)
    value.deep_stringify_keys!
 
    kms_encrypt_sensitive_paths!(value, SENSITIVE_PATHS)
    alert_or_raise_if_contains_sensitive_keys!(value)
    plain = JSON.generate(value)
    alert_or_raise_if_contains_sensitive_value!(plain, value)
 
    if should_compress?(plain)
      {
        VERSION_KEY => CIPHERTEXT_HEADER,
        CIPHERTEXT_KEY => outer_encrypt(Zlib.gzip(plain)),
        COMPRESSED_KEY => 1,
      }.to_msgpack
    else
      {
        VERSION_KEY => CIPHERTEXT_HEADER,
        CIPHERTEXT_KEY => outer_encrypt(plain),
        COMPRESSED_KEY => 0,
      }.to_msgpack
    end
  end
 
  def kms_encrypt(text)
    Base64.encode64(kms_client.encrypt(text, 'context' => 'session-encryption'))
  end
 
  def kms_decrypt(text)
    kms_client.decrypt(Base64.decode64(text), 'context' => 'session-encryption')
  end
 
  def kms_client
    Encryption::KmsClient.new(kms_key_id: IdentityConfig.store.aws_kms_session_key_id)
  end
 
  def outer_encrypt(plaintext)
    Encryption::Encryptors::AesEncryptorV2.new.encrypt(plaintext, session_encryption_key)
  end
 
  def outer_decrypt(ciphertext)
    Encryption::Encryptors::AesEncryptorV2.new.decrypt(ciphertext, session_encryption_key)
  end
 
  private
 
  # This method extracts all of the sensitive paths that exist into a
  # separate hash.  This separate hash is then encrypted and placed in the session.
  # We use #reduce to build the nested empty hash if needed. If Hash#bury
  # (https://bugs.ruby-lang.org/issues/11747) existed, we could use that instead.
  def kms_encrypt_sensitive_paths!(session, sensitive_paths)
    sensitive_data = {}
 
    sensitive_paths.each do |path|
      all_but_last_key = path[0..-2]
      last_key = path.last
 
      if all_but_last_key.blank?
        value = session.delete(last_key)
      else
        value = session.dig(*all_but_last_key)&.delete(last_key)
      end
 
      if value
        all_but_last_key.reduce(sensitive_data) do |hash, key|
          hash[key] ||= {}
 
          hash[key]
        end
 
        if all_but_last_key.blank?
          sensitive_data[last_key] = value
        else
          sensitive_data.dig(*all_but_last_key).store(last_key, value)
        end
      end
    end
 
    raise "invalid session, 'sensitive_data' is reserved key" if session['sensitive_data'].present?
    return if sensitive_data.blank?
    session['sensitive_data'] = kms_encrypt(JSON.generate(sensitive_data))
  end
 
  # This method reverses the steps taken in #kms_encrypt_sensitive_paths!
  # The encrypted hash is decrypted and then deep merged into the session hash.
  # The merge must be a deep merge to avoid collisions with existing hashes in the
  # session.
  def kms_decrypt_sensitive_paths!(session)
    sensitive_data = session.delete('sensitive_data')
    return if sensitive_data.blank?
 
    sensitive_data = JSON.parse(
      kms_decrypt(sensitive_data),
    )
 
    session.deep_merge!(sensitive_data)
  end
 
  def alert_or_raise_if_contains_sensitive_value!(string, hash)
    if SENSITIVE_REGEX.match?(string)
      exception = SensitiveValueError.new
      if IdentityConfig.store.session_encryptor_alert_enabled
        NewRelic::Agent.notice_error(
          exception, custom_params: {
            session_structure: hash.deep_transform_values { |_v| nil },
          }
        )
      else
        raise exception
      end
    end
  end
 
  def alert_or_raise_if_contains_sensitive_keys!(hash)
    hash.deep_transform_keys do |key|
      if SENSITIVE_KEYS.include?(key.to_s)
        exception = SensitiveKeyError.new("#{key} unexpectedly appeared in session")
        if IdentityConfig.store.session_encryptor_alert_enabled
          NewRelic::Agent.notice_error(
            exception, custom_params: {
              session_structure: hash.deep_transform_values { |_v| '' },
            }
          )
        else
          raise exception
        end
      end
    end
  end
 
  def should_compress?(value)
    value.bytesize >= MINIMUM_COMPRESS_LIMIT
  end
 
  def session_encryption_key
    IdentityConfig.store.session_encryption_key
  end
end