Yes indeed, that chain of exploits was all software and not hardware. Developed after the Hotz exploit and Sony subsequently shuttering OtherOS.

It didn't directly give access to anything however. IIRC they heavily relied on other complex exploits they developed themselves, as well as relying on earlier exploits they could access by rolling back the firmware by indeed abusing the ECDSA implementation. At least, that turned out to be the path of least resistance. Without earlier exploits, there would be less known about the system to work with.

Their presentation [1] [2] is still a very interesting watch.

[1] https://www.youtube.com/watch?v=5E0DkoQjCmI

[2] https://fahrplan.events.ccc.de/congress/2010/Fahrplan/attach...