Fedora to disallow CC0-licensed code

You're not going to be able to trace provenance back further. Jean-Philippe Aumasson and DJB came up with SipHash in 2012, the CC0 code is their reference implementation. Obviously Aumasson and DJB aren't going to have patented this, but the nature of patents means that's not necessarily enough.

On the other hand, it's an ARX algorithm, this is not rocket surgery, it seems to me that if you insist on having a C implementation you could just write one, fulfilling the same API as the reference implementation, and acknowledge the algorithm's inventors then write BSD-0 or whatever at the top.

I think this meets the common good requirement (like the Ogg Vorbis and Ogg Opus codecs) so that BSD-0 is appropriate even for someone like me who thinks the GPL is generally better.