There's actually quite a bit of information about the development of the F-117, as well as the science and math that made it possible: https://www.f117sfa.org/f117-development
The base of the research was deemed to be of no significant military or economic value by the USSR so it was published internationally.
https://en.wikipedia.org/wiki/Petr_Ufimtsev#The_father_of_st...
Sure, 40 years later its all out in the open, but that's because there's no longer a reason to keep it secret.