I cannot verify a gpg signature for your Focal image. It could be my error, of course. But for Buster, all works perfectly by the same methods.

 

Something about the Focal download is different and undocumented, or something is just plain wrong. (Buster and Focal are zipped with different programs. What's up with that?)

 

Yesterday, attempting to verify the Focal image from the main download by similar steps led to a runaway output (symbols, code) in terminal. That scared me. I shut down the virtual machine, then deleted it.

 

Tried again today (below). All done in a fresh virtual machine. Files for checking (.asc, .img) downloaded by wget from links at base of Downloads page.

 

Public key downloaded according to your webpage https://docs.armbian.com/User-Guide_Getting-Started/#how-to-check-download-authenticity.

 

1. Download from Denmark mirror:

[user@d-nanopi-m4-v2 focal]$ wget http://mirrors.dotsrc.org/armbian-dl/nanopim4v2/archive/Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.xz
--2020-06-02 15:30:38--  http://mirrors.dotsrc.org/armbian-dl/nanopim4v2/archive/Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.xz
Resolving mirrors.dotsrc.org (mirrors.dotsrc.org)... 130.225.254.116, 2001:878:346::116
Connecting to mirrors.dotsrc.org (mirrors.dotsrc.org)|130.225.254.116|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 771774000 (736M) [application/octet-stream]
Saving to: ‘Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.xz’

Armbian_20.05.1_Nan 100%[===================>] 736.02M  3.94MB/s    in 3m 14s  

2020-06-02 15:33:53 (3.80 MB/s) - ‘Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.xz’ saved [771774000/771774000]

2. Unzip (as per instructions) and list folder contents

[user@d-nanopi-m4-v2 focal]$ xz -d Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.xz

[user@d-nanopi-m4-v2 focal]$ ls
Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img
Focal_current_desktop.asc
Focal_current_desktop.sha

3. Fail gpg verify

[user@d-nanopi-m4-v2 focal]$ gpg --verify Focal_current_desktop.asc Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img
gpg: Signature made Sun May 31 06:59:23 2020 AEST
gpg:                using RSA key DF00FAF1C577104B50BF1D0093D6889F9F0E78D5
gpg: BAD signature from "Igor Pecovnik <igor@armbian.com>" [unknown]

4. Trying to test .asc file - fail

[user@d-nanopi-m4-v2 focal]$ gpg --keyid-format long --list-options show-keyring Focal_current_desktop.asc
gpg: WARNING: no command supplied.  Trying to guess what you mean ...
Detached signature.
Please enter name of data file: Focal_current_desktop.asc
gpg: Signature made Sun May 31 06:59:23 2020 AEST
gpg:                using RSA key DF00FAF1C577104B50BF1D0093D6889F9F0E78D5
gpg: BAD signature from "Igor Pecovnik <igor@armbian.com>" [unknown]

5. Change name and try to verify again - fail. x2
 

[user@d-nanopi-m4-v2 focal]$ cp Focal_current_desktop.asc Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.asc

[user@d-nanopi-m4-v2 focal]$ gpg --verify Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.asc Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img
gpg: Signature made Sun May 31 06:59:23 2020 AEST
gpg:                using RSA key DF00FAF1C577104B50BF1D0093D6889F9F0E78D5
gpg: BAD signature from "Igor Pecovnik <igor@armbian.com>" [unknown]

[user@d-nanopi-m4-v2 focal]$ gpg --verify Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img.asc
gpg: assuming signed data in 'Armbian_20.05.1_Nanopim4v2_focal_current_5.4.43_desktop.img'
gpg: Signature made Sun May 31 06:59:23 2020 AEST
gpg:                using RSA key DF00FAF1C577104B50BF1D0093D6889F9F0E78D5
gpg: BAD signature from "Igor Pecovnik <igor@armbian.com>" [unknown]

 

2 hours ago, bad_img said:

Something about the Focal download is different and undocumented, or something is just plain wrong

We are changing docs about that ... not finished yet, but you can find some clues. Also Focal images - you should not fail to see the warning - are corrupted.

https://github.com/armbian/documentation/pull/74

 

2 hours ago, bad_img said:

Something about the Focal download is different and undocumented, or something is just plain wrong. (Buster and Focal are zipped with different programs. What's up with that?)

You can find explanation here https://www.armbian.com/newsflash/armbian-20-05-kagu/