Dear Tiago, I am on Ubuntu 16.04 and while updating I got the following error. Err:16 http://downloads.skewed.de/apt/xenial xenial Release.gpg The following signatures were invalid: BADSIG 7A80C8ED4FCCBE09 Tiago de Paula Peixoto <tiago@skewed.de> So as per the instructions page, I tried: sudo apt-key adv --keyserver pgp.skewed.de --recv-key 612DEFB798507F25 However, this returns the following: Executing: /tmp/tmp.UgWxLPVkr2/gpg.1.sh --keyserver pgp.skewed.de --recv-key 612DEFB798507F25 gpg: requesting key 98507F25 from hkp server pgp.skewed.de gpgkeys: key 612DEFB798507F25 can't be retrieved gpg: no valid OpenPGP data found. gpg: Total number processed: 0 gpg: keyserver communications error: keyserver helper general error gpg: keyserver communications error: unknown pubkey algorithm gpg: keyserver receive failed: unknown pubkey algorithm What can be done? Thank you -- Snehal M. Shekatkar Pune India