[arch-general] broken package stops pacstrap

[mick howe]

Trying to install arch i686 on my IBM x345 using 2015 07 install media (yes
I know its 2 years old). Get as far as running pacstrap and it comes to a
crashing halt on checking package integrity

error: krb5 : signature from "Levente Polyak (anthraxx)
levente at leventepolyak.net> " is unknown trust
:: File /mnt/var/cache/pacman/pkg/krb5-1.15.1-1-i686.pkg.tar.xz is
corrupted (invalid or corrupted package PGP signature)).

How can I get past this crash

mick in glen innes