# File lib/net/ntlm_http.rb, line 215
      def lmv2_response(arg, opt = {})
        key = arg[:ntlmv2_hash]
        chal = arg[:challenge]
        
        chal = NTLM::pack_int64le(chal) if chal.is_a?(Integer)

        if opt[:client_challenge]
          cc  = opt[:client_challenge]
        else
          cc = rand(MAX64)
        end
        cc = NTLM::pack_int64le(cc) if cc.is_a?(Integer)

        OpenSSL::HMAC.digest(OpenSSL::Digest::MD5.new, key, chal + cc) + cc
      end