W: There are no public key available for the following key IDs

If you just ran apt-get update and you got:

There are no public key available for the following key IDs:
A70DAF536070D3A1

then type:

sudo gpg --recv-key --keyserver wwwkeys.eu.pgp.net A70DAF536070D3A1
sudo gpg --export A70DAF536070D3A1 | apt-key add -

and all will be well.