anchor.diff:  
   prop_box_correct() ->
       ?FORALL({Msg, Nonce, {PK1, SK1}, {PK2, SK2}},
  -            {g_iodata(),
  +            {fault_rate(1, 40, g_iodata()),
                fault_rate(1, 40, nonce()),
                fault_rate(1, 40, keypair()),
                fault_rate(1, 40, keypair())},
  
positive.code: 
  prop_stream_xor_correct() ->
      ?FORALL({Msg, Nonce, Key},
              {g_iodata(),
               fault_rate(1, 40, nonce()),
               fault_rate(1, 40, secret_key())},
          case v_iodata(Msg) andalso nonce_valid(Nonce) andalso secret_key_valid(Key) of
  
negative.code: 
  ot_authenticator_good(Msg, Key) when is_binary(Key) ->
      Sz = enacl:secretbox_key_size(),
      case v_iodata(Msg) andalso byte_size(Key) == Sz of
        true ->
          frequency([{1, ?LAZY({invalid, binary(enacl:onetime_auth_size())})},
                     {3, return({valid, enacl:onetime_auth(Msg, Key)})}]);
  