Replace your /etc/apt/sources.list
with:
deb http://http.debian.net/debian/ jessie main
deb http://http.debian.net/debian/ jessie-backports main
deb http://security.debian.org/ jessie/updates main
Then I'd also run:
sudo apt-key update -y
sudo apt-get update -y
sudo apt-get upgrade -y
That should do the trick.
@source: https://www.lowendtalk.com/discussion/62567/apt-get-hash-sum-mismatch-debian-jessie