anchor.diff:  
   %% Generator for binaries of a given size with different properties and fault injection:
   g_binary(Sz) ->
  -    fault(g_binary_bad(Sz), g_binary_good(Sz)).
  +    z_fault(g_binary_bad(Sz), g_binary_good(Sz)).
   
   g_binary_good(Sz) when Sz =< 32 -> binary(Sz);
   g_binary_good(Sz) -> eqc_gen:largebinary(Sz).
  
positive.code: 	       ?SUCHTHAT(B, binary(), byte_size(B) /= enacl:secretbox_key_size())]).
  
  secret_key() ->
  	fault(secret_key_bad(), secret_key_good()).
  
  secret_key_valid(SK) when is_binary(SK) ->
  	Sz = enacl:secretbox_key_size(),
  
negative.code: 
  prop_afternm_correct() ->
      ?FORALL([Msg, Nonce, Key],
          [z_fault_rate(1, 40, g_iodata()),
           z_fault_rate(1, 40, nonce()),
           z_fault_rate(1, 40, beforenm_key())],
        begin
            case v_iodata(Msg) andalso nonce_valid(Nonce) andalso v_key(Key) of
                true ->
  