I do and get# http://stackoverflow.com/a/10260634/54964root@masi:/home/masi/Documents# gpg --keyserver subkeys.pgp.net --recv-key  06F90DE5381BA480gpg: directory `/root/.gnupg' createdgpg: new configuration file `/root/.gnupg/gpg.conf' createdgpg: WARNING: options in `/root/.gnupg/gpg.conf' are not yet active during this rungpg: keyring `/root/.gnupg/secring.gpg' createdgpg: keyring `/root/.gnupg/pubring.gpg' createdgpg: requesting key 381BA480 from hkp server subkeys.pgp.net?: subkeys.pgp.net: Network is unreachablegpgkeys: HTTP fetch error 7: couldn't connect: Network is unreachablegpg: no valid OpenPGP data found.gpg: Total number processed: 0I am trying to change to R backports because I need R 3.3.2, so I did already the addition of the following line in /etc/apt/sources.listdeb http://cran.wu.ac.at/bin/linux/debian jessie-cran3/Iterating rcs' proposalroot@masi:/home/masi/Documents# gpg --keyserver keys.gnupg.net --recv-key 06F90DE5381BA480gpg: requesting key 381BA480 from hkp server keys.gnupg.netgpg: /root/.gnupg/trustdb.gpg: trustdb createdgpg: key 381BA480: public key Johannes Ranke (CRAN Debian archive) <jranke@uni-bremen.de> importedgpg: no ultimately trusted keys foundgpg: Total number processed: 1gpg:               imported: 1root@masi:/home/masi/Documents# apt-get update...Fetched 116 kB in 3s (32.1 kB/s)         Reading package lists... DoneW: GPG error: http://cran.wu.ac.at jessie-cran3/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 06F90DE5381BA480OS: Debian 8.5     
Why failing to get CRAN key for R backports?
debian;software installation;key authentication;r
See the installation instructions for Debian packages on CRAN, section Secure apt:The Debian backports archives on CRAN are signed with the key of  Johannes Ranke (CRAN Debian archive) with key  fingerprint 6212 B7B7 931C 4BB1 6280  BA13 06F9 0DE5 381B A480. You  can fetch and import this withapt-key adv --keyserver keys.gnupg.net --recv-key 6212B7B7931C4BB16280BA1306F90DE5381BA480