Leaked encryption keys for example come to mind, but I'm sure there's other examples.
E: I realise after digging it back up it's what you said with encryption keys but maybe someone else wants to look at the link too or whatever
https://en.wikipedia.org/wiki/AACS_encryption_key_controvers...
They tried to censor the blu-ray key, but that survived 3 years before bitcoin was invented
Leaked encryption keys for example come to mind, but I'm sure there's other examples.