Ask HN: What did Sony do wrong with PS3 signing?

Background info: https://arstechnica.com/gaming/2010/12/ps3-hacked-through-poor-implementation-of-cryptography/

From the article:

> But when fail0verflow worked backwards from generated keys, they found out that a parameter that should have been randomized for each key generation wasn't being randomized at all. Instead, the PS3 was using the same number for that variable, every single time, making it easy to work out acceptable keys.

Which parameter are they talking about? Seed?