step 1 : sudo pacman-key --lsign-key "Levon 'noptrix' Kayan (BlackArch Developer) <[email protected]>"

step 2 : sudo pacman-key --keyserver keyserver.ubuntu.com --recv-keys 4345771566D76038C7FEB43863EC0ADBEA87E4E3

sudo pacman-key --lsign-key 4345771566D76038C7FEB43863EC0ADBEA87E4E3

step 3 : sudo nano /etc/pacman.d/blackarch-mirrorlist

Step 4 : reboot

step 5 : sudo pacman -Syyu