This is fixed by avoiding https and using the insecure http instead. Running this worked for me.
gem source -a http://rubygems.org/
rvm osx-ssl-certs update all
did the trick for me, ruby 2.0.0
Try using http://rubygems.org/ (without SSL) as a source — that fixed the error for me.
gem source -r https://rubygems.org/gem source -a http://rubygems.org/gem install cocoapods