# File lib/net/ntlm/client/session.rb, line 60
      def sign_message(message)
        seq = sequence
        sig = OpenSSL::HMAC.digest(OpenSSL::Digest::MD5.new, client_sign_key, "#{seq}#{message}")[0..7]
        if negotiate_key_exchange?
          sig = client_cipher.update sig
          sig << client_cipher.final
        end
        "#{VERSION_MAGIC}#{sig}#{seq}"
      end