If you build a tool _for explicit illegal purposes_, ... well that's not really the same as building tools that can be used for illegal purposes, is it?
Once again, depends on who you ask.
By international laws (Universal Declaration of Human Rights) it has been illegal starting 19481[1].
USA, however, still struggled with racial segregation until the 1960s and until then wasn't really illegal in the States. In South Africa, it probably wasn't illegal either as the government made the law themselves.