invalid or corrupted package (PGP signature) on archlinux

Answer is originally from this page:

https://bbs.archlinux.org/viewtopic.php?id=68497

List master key

 pacman-key --list-sigs Master

Found system build is [unknown]

[root@alarm pacman.d]# pacman-key --list-sigs 
/etc/pacman.d/gnupg/pubring.gpg
-------------------------------
pub   rsa2048 2018-07-03 [SC]
      FD785384A109FD5D1EE05C5991C14EDA20BECC7D
uid           [ultimate] Pacman Keyring Master Key 
sig 3        91C14EDA20BECC7D 2018-07-03  Pacman Keyring Master Key 

pub   rsa4096 2014-01-18 [SC]
      68B3537F39A313B3E574D06777193F152BDBE6A6
uid           [ unknown] Arch Linux ARM Build System 
sig          1BB89C0602367449 2018-01-16  [User ID not found]
sig          BF7EEF7A9C6B5765 2014-01-18  [User ID not found]
sig          BC704E86B823CD25 2014-01-18  [User ID not found]
sig          B55C5315DCD9EE1A 2014-01-18  [User ID not found]
sig 2        AB4311039017FB32 2017-09-25  [User ID not found]
sig 3        77193F152BDBE6A6 2014-01-18  Arch Linux ARM Build System 
sub   rsa4096 2014-01-18 [E]
sig          1BB89C0602367449 2018-01-16  [User ID not found]
 

Fixed by running :

pacman-key --lsign-key 68B3537F39A313B3E574D06777193F152BDBE6A6 

root@alarm pacman.d]# pacman-key --lsign-key 68B3537F39A313B3E574D06777193F152BDBE6A6
  -> Locally signing key 68B3537F39A313B3E574D06777193F152BDBE6A6...
==> Updating trust database...
gpg: marginals needed: 3  completes needed: 1  trust model: pgp
gpg: depth: 0  valid:   1  signed:   1  trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: depth: 1  valid:   1  signed:   0  trust: 1-, 0q, 0n, 0m, 0f, 0u