Is there any chance to get SHA256 running in v10.3.?

… as my question says clearly.

I'm running an old iBook G4 with 10.3.9 (actually it belongs to a friend) and 256 MB RAM.

My online provider just changed certificates to SHA256 encryption which seems to be incompatible to Panther in general.

As far as I learned from the net, the minimum OS for SHA256 compatability is 10.5 ...

Well, even if I'm quite experienced with Macs, I'm not familiar with terminal or unix commands.

Therefore I would need advice suitable for a dummy. :-)

Thanks for any suggestions!

Sven