Can't install graph_tool authentication key error

Hello, i can't install graph_tool on Ubuntu even though i added the

deb http://downloads.skewed.de/apt/bionic bionic universe
deb-src http://downloads.skewed.de/apt/bionic bionic universe

When running

apt-key adv --keyserver pgp.skewed.de --recv-key 612DEFB798507F25 to add the key,

I get:

Executing: /tmp/apt-key-gpghome.ublSytc17X/gpg.1.sh --keyserver pgp.skewed.de --recv-key 612DEFB798507F25 gpg: keyserver receive failed: Connection timed out

And when i try to run

apt-get install python3-graph-tool

Of course i get this message:

Reading state information... Done E: Unable to locate package python3-graph-tool