What kind of Republic-era institutions would the ISB have been built upon?

In a lot of Star Wars media, particularly Andor, the ISB is depicted as a very large, complex institution with a very large pool of resources and support/leadership from very high-ranking members of the Imperial bureaucracy, i.e. Krennic and Yularen, among others. But where did the institution actually come from? Was it built upon Republic intelligence agencies set up by Palpatine or was it a completely new structure created post-war?