I was trying to verify the iso image after dowloading the Discreete Linux.
I carefully followed the instructions from Discreete website: https://www.discreete-linux.org/howto.html#use_pre
That means that I dowloaded Discreete Linux 2016.01_Beta1 signature of the ISO image and Discreete Linux signing key (2016) as well as the .iso itself, and I left it all in the Dowloads folder. While executing the command I got the following mistake:
user@user-PC:~/Downloads$ gpg --keyid-format 0xlong --verify
Discreete_Linux_2016.1_beta1.hybrid.iso.asc
Discreete_Linux_2016.1_beta1.hybrid.iso
gpg: Signature made Чт 08 дек 2016 09:27:53 GMT
gpg: using RSA key 0xBA146BB0759613AC
gpg: Can't check signature: public key not found