gpg --keyid-format 0xlong --verify tails-amd64-3.6.iso.sig tails-amd64-3.6.iso

gpg: Signature made Tue 13 Mar 2018 11:41:20 AEDT
gpg:                using RSA key 0x3020A7A9C2B72733
gpg: Good signature from "Tails developers <tails@boum.org>"
gpg:                 aka "Tails developers (offline long-term identity key) <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: 2FAF 9BA0 D65B B371 F0BC  2D46 3020 A7A9 C2B7 2733

gpg --keyid-format 0xlong --verify tails-amd64-3.6.1.iso.sig tails-amd64-3.6.1.iso

gpg: Signature made Sat 17 Mar 2018 11:08:42 AEDT
gpg:                using ? key 0x90B2B4BD7AED235F
gpg: Can't check signature: unknown pubkey algorithm