nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ ls -l
total 1181296
-rw-r--r-- 1 nirvana nirvana 1209116672 Jul 13 14:39 tails-amd64-3.0.1.iso
-rw-r--r-- 1 nirvana nirvana        833 Jul 13 14:36 tails-amd64-3.0.1.iso.sig
-rw-rw-r-- 1 nirvana nirvana     459593 Jul 21 15:20 tails-signing.key
nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ gpg --import < tails-signing.key
gpg: key 58ACD84F: "Tails developers (offline long-term identity key) <tails@boum.org>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1
nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ sudo aptitude install debian-keyring
debian-keyring is already installed at the requested version (2016.01.20)
debian-keyring is already installed at the requested version (2016.01.20)
No packages will be installed, upgraded, or removed.
0 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B of archives. After unpacking 0 B will be used.

nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ gpg --keyring=/usr/share/keyrings/debian-keyring.gpg --export zack@upsilon.cc | gpg --import
gpg: key 6D866396: "Stefano Zacchiroli <zack@upsilon.cc>" not changed
gpg: key 6D866396: "Stefano Zacchiroli <zack@upsilon.cc>" not changed
gpg: Total number processed: 2
gpg:              unchanged: 2
nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ gpg --keyid-format 0xlong --check-sigs A490D0F4D311A4153E2BB7CADBB802B258ACD84F
pub   4096R/0xDBB802B258ACD84F 2015-01-18 [expires: 2018-01-11]
uid                            Tails developers (offline long-term identity key) <tails@boum.org>
sig!3        0xDBB802B258ACD84F 2015-01-18  Tails developers (offline long-term identity key) <tails@boum.org>
sig!         0x9C31503C6D866396 2015-02-03  Stefano Zacchiroli <zack@upsilon.cc>
sig!3        0xDBB802B258ACD84F 2015-09-27  Tails developers (offline long-term identity key) <tails@boum.org>
sig!3        0xDBB802B258ACD84F 2016-08-30  Tails developers (offline long-term identity key) <tails@boum.org>
uid                            Tails developers <tails@boum.org>
sig!3        0xDBB802B258ACD84F 2015-09-27  Tails developers (offline long-term identity key) <tails@boum.org>
sig!3        0xDBB802B258ACD84F 2016-08-30  Tails developers (offline long-term identity key) <tails@boum.org>
sub   4096R/0x98FEC6BC752A3DB6 2015-01-18 [expires: 2018-01-11]
sig!         0xDBB802B258ACD84F 2016-08-30  Tails developers (offline long-term identity key) <tails@boum.org>
sub   4096R/0x3C83DCB52F699C56 2015-01-18 [expires: 2018-01-11]
sig!         0xDBB802B258ACD84F 2016-08-30  Tails developers (offline long-term identity key) <tails@boum.org>
sub   4096R/0xAF292B44A0EDAA41 2016-08-30 [expires: 2018-01-11]
sig!         0xDBB802B258ACD84F 2016-08-30  Tails developers (offline long-term identity key) <tails@boum.org>

727 signatures not checked due to missing keys
nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $ gpg --keyid-format 0xlong --verify tails-amd64-3.0.1.iso.sig tails-amd64-3.0.1.iso
gpg: Signature made Tue 04 Jul 2017 11:41:53 PM +09
gpg:                using RSA key 0x98FEC6BC752A3DB6
gpg: Good signature from "Tails developers (offline long-term identity key) <tails@boum.org>"
gpg:                 aka "Tails developers <tails@boum.org>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: A490 D0F4 D311 A415 3E2B  B7CA DBB8 02B2 58AC D84F
     Subkey fingerprint: BA2C 222F 44AC 00ED 9899  3893 98FE C6BC 752A 3DB6
nirvana@nirvana-HP-250-G2-Notebook-PC ~/Downloads/tails-amd64-3.0.1 $