I installed the Citrix receiver (receiver.citrix.com) .deb file successfully on my newly installed 12.04.2LTS x64 laptop. Unfortunately the POC for citrix had a self-signed certificate.

I was receiving Error 61 that the certificate was untrusted and I had to quit the application.

Ended up copying the root certificate over to /usr/local/share/ca-certificates, changing the name, and running the cert update. This did not fix my issue, but it’s good to know anyway:

SSH as root, or add sudo before all commands
cp YOURCERTFILE.cer /usr/local/share/ca-certificates/
cd /usr/local/share/ca-certificates
mv YOURCERTFILE.cer YOURCERTFILE.crt
update-ca-certificates

Since that did not work, now I went on looking for the certificate store on the Citrix side:
cp YOURCERTFILE.crt /opt/Citrix/ICAClient/keystore/cacerts/

Try your xendesktop or xenapp now. Magic bananas.