What you say is true. But security through obscurity doesn't work, because people are very good at reverse engineering and decompiling. So your choices are ei

What you say is true. But security through obscurity doesn't work, because people are very good at reverse engineering and decompiling. So your choices are either: open source your crypto code and suffer some embarrassments which people will forget and forgive, or have closed source crypto code that either doesn't work or can be exploited in subtle ways. Pick your poison. :)