Kali Linux / Parrot Security OS (updated Mar, 2018)

If you are getting the following error:

Invalid signature for Kali Linux repositories : “The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository”

 There are 2 possibilities:

gpg --keyserver hkp://keys.gnupg.net --recv-key 7D8D0BF6

gpg --fingerprint 7D8D0BF6

gpg -a --export 7D8D0BF6 | apt-key add - 

apt update  

update :  03 Mar , 2018.
Answer from the official documentation :

Note that if you haven’t updated your Kali installation in some time (tsk2), you will like receive a GPG error about the repository key being expired (ED444FF07D8D0BF6). Fortunately, this issue is quickly resolved by running the following as root:

wget -q -O - https://archive.kali.org/archive-key.asc | apt-key add

KALI Linux on Windows APP!

Win Shell: 

Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux

apt-get update  
apt-get dist-upgrade

apt-get update
apt-get install metasploit-framework