extract_encoded

# File activesupport/lib/active_support/message_verifier.rb, line 314
      def extract_encoded(signed)
        if signed.nil? || !signed.valid_encoding?
          throw :invalid_message_format, "invalid message string"
        end

        if separator_index = separator_index_for(signed)
          encoded = signed[0, separator_index]
          digest = signed[separator_index + SEPARATOR_LENGTH, digest_length_in_hex]
        end

        unless digest_matches_data?(digest, encoded)
          throw :invalid_message_format, "mismatched digest"
        end

        encoded
      end