fucking hell 
aradis# pacman -Syyu
error: obcore: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: obcommunity: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: observice: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
:: Synchronising package databases...
 obcore                 26.9 KiB  1345 KiB/s 00:00 [# #####################] 100%
 obcore.sig            310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: obcore: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update obcore (invalid or corrupted database (PGP signature))
 obextra                82.3 KiB  2.01 MiB/s 00:00 [# #####################] 100%
 obextra.sig           310.0   B  0.00   B/s 00:00 [# #####################] 100%
 obcommunity            18.5 KiB  0.00   B/s 00:00 [# #####################] 100%
 obcommunity.sig       310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: obcommunity: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update obcommunity (invalid or corrupted database (PGP signature))
 obmultilib              3.1 KiB  0.00   B/s 00:00 [# #####################] 100%
 obmultilib.sig        310.0   B  0.00   B/s 00:00 [# #####################] 100%
 observice              23.2 KiB  0.00   B/s 00:00 [# #####################] 100%
 observice.sig         310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: observice: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update observice (invalid or corrupted database (PGP signature))
 core                  133.0 KiB  1662 KiB/s 00:00 [# #####################] 100%
 extra                1651.0 KiB  4.24 MiB/s 00:00 [# #####################] 100%
 community               5.3 MiB  5.52 MiB/s 00:01 [# #####################] 100%
 multilib              152.5 KiB  4.96 MiB/s 00:00 [# #####################] 100%
error: failed to synchronize all databases
Please provide the output of the following command
date
and watch your vocabulary
I have it all mixed up because i had to take that yellow battery from the laptop... 
Wed 20 Jan 19:40:30 GMT 2021
I thought you may have the date turned back to 2020 or something else, that would invalidate the certificates.
There is no problem on the mirror side, everything is working fine. How did you do this installation? Is obarun-keyring installed? If not edit pacman.conf switch SigLevel = Required to Never, install the keyring, then switch back
Still the same 
paradis# nano /etc/pacman.conf
paradis# pacman -Sy obarun-keyring
:: Synchronising package databases...
 obcore is up to date
 obextra is up to date
 obcommunity is up to date
 obmultilib is up to date
 observice is up to date
 core is up to date
 extra is up to date
 community is up to date
 multilib is up to date
warning: obarun-keyring-20200709-1 is up to date -- reinstalling
resolving dependencies...
looking for conflicting packages...

Packages (1) obarun-keyring-20200709-1

Total Download Size:   0.01 MiB
Total Installed Size:  0.00 MiB
Net Upgrade Size:      0.00 MiB

:: Proceed with installation? [Y/n] y
:: Retrieving packages...
 obarun-keyring-2...     5.8 KiB  0.00   B/s 00:00 [# #####################] 100%
(1/1) checking keys in keyring                     [# #####################] 100%
(1/1) checking package integrity                   [# #####################] 100%
(1/1) loading package files                        [# #####################] 100%
(1/1) checking for file conflicts                  [# #####################] 100%
(1/1) checking available disk space                [# #####################] 100%
:: Processing package changes...
(1/1) reinstalling obarun-keyring                  [# #####################] 100%
==> Appending keys from obarun.gpg...
==> Locally signing trusted keys in keyring...
  -> Locally signing key B0653E62982DBDAF1BCB82AF3D57B0F2754E2034...
  -> Locally signing key 1E389882EFEABB1AE7723A014B9100E679075EDF...
==> Importing owner trust values...
==> Disabling revoked keys in keyring...
  -> Disabling key 5FF0C09152A95D743BFD60A402FD193357C6A9B6...
  -> Disabling key 6DD4217456569BA711566AC7F06E8FDE7B45DAAC...
  -> Disabling key EE62628C5670B472C1529563D4CA511F0375F9B2...
==> Updating trust database...
gpg: no need for a trustdb check
paradis# nano /etc/pacman.conf
paradis# pacman -Syyu
error: obcore: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: obcommunity: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: observice: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
:: Synchronising package databases...
 obcore                 26.9 KiB  1345 KiB/s 00:00 [# #####################] 100%
 obcore.sig            310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: obcore: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update obcore (invalid or corrupted database (PGP signature))
 obextra                82.3 KiB  2.01 MiB/s 00:00 [# #####################] 100%
 obextra.sig           310.0   B  0.00   B/s 00:00 [# #####################] 100%
 obcommunity            18.5 KiB  0.00   B/s 00:00 [# #####################] 100%
 obcommunity.sig       310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: obcommunity: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update obcommunity (invalid or corrupted database (PGP signature))
 obmultilib              3.1 KiB  0.00   B/s 00:00 [# #####################] 100%
 obmultilib.sig        310.0   B  0.00   B/s 00:00 [# #####################] 100%
 observice              23.2 KiB  0.00   B/s 00:00 [# #####################] 100%
 observice.sig         310.0   B  0.00   B/s 00:00 [# #####################] 100%
error: observice: signature from "Eric Vidal <eric@ obarun.org>" is unknown trust
error: failed to update observice (invalid or corrupted database (PGP signature))
 core                  133.0 KiB  1662 KiB/s 00:00 [# #####################] 100%
 extra                1651.0 KiB  4.36 MiB/s 00:00 [# #####################] 100%
 community               5.3 MiB  5.96 MiB/s 00:01 [# #####################] 100%
 multilib              152.5 KiB  4.96 MiB/s 00:00 [# #####################] 100%
error: failed to synchronize all databases
I spilled some coffee on my keyboard few days ago so laptop stopped running... So i had to take keyboard out to dry up and that small battery inside that laptop... Now when i boot obarun the dates are like february 2117 or 2127...
So first time i booted into obarun i tried to update system but i haven't noticed that date was wrong...
maybe i should just update sigrequired to never....
This is funny, obextra obmultilib are not having a problem ..
# pacman-key --populate obarun archlinux
# pacman-db-upgrade
# pacman -Syy

The signatures are kept in:
% lsd /var/lib/pacman/sync/ob*.db.sig

-rw-r--r-- 1 root root 310 Dec 21 09:10 /var/lib/pacman/sync/obcommunity.db.sig
-rw-r--r-- 1 root root 310 Dec 22 09:49 /var/lib/pacman/sync/obcore.db.sig
-rw-r--r-- 1 root root 310 Jan 12 08:38 /var/lib/pacman/sync/observice.db.sig
-rw-r--r-- 1 root root 310 Jan 17 16:08 /var/lib/pacman/sync/obextra.db.sig
-rw-r--r-- 1 root root 310 Jan 17 20:37 /var/lib/pacman/sync/obmultilib.db.sig

if you don't have those three that means it asked you at some point to download the signatures and you responded "no"

so you have the .db files of each repository and a signature that validates the .db

All I can tell you is delete all the .db and .db.sig files in the directory and pacman -Syy and get fresh and also say Y to downloading signature files.
# rm -rf /etc/pacman.d/gnupg
# pacman-key --init
# pacman-key --populate archlinux obarun
# pacman -Syy

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