Just a quick post – If you want to download a file using wget from a server that has an invalid SSL certificate (expired, not from a trusted issuer etc) then you can use the  --no-check-certificate flag to make wget ignore such errors.

It’s worth noting that you shouldn’t blindly ignore certificate errors. If you’re downloading from what is normally a trusted source and have no reason to expect to be presented with an invalid cert, then further investigation is due.