If you are using Kali and have issues downloading packages or even doing an update && upgrade then there is a solution.
This is normally an issue if you run Kali Linux in Virtual box on Windows at the same time as Hyper-V or Docker.
To fix the issue run the following commands in Kali
$ sudo bash # mkdir /etc/gcrypt # echo all > /etc/gcrypt/hwf.deny
Now run sudo apt-get update && upgrade again. Everything should now be working