Make sure you download from an official Kali Linux mirror.
For more information see the documentation.
The latest hashes can be found here: http://cdimage.kali.org/current/.
These are all SHA-1 hashes.
Kali Linux Rolling 2018.2
Code:
e7cdca1f84674df2fc2ad57f781d55e1fc53d46e kali-linux-2018.2-amd64.iso
304565cca360479b6ade801aed2e672fced42e7b kali-linux-2018.2-i386.iso
34d40e4afe26ed23fa9d37ee84e4d3f3ecff5ec0 kali-linux-light-2018.2-amd64.iso
e9bf41df47e1e09658c27a006d4d4cb03f96bcd9 kali-linux-light-2018.2-i386.iso
5998f694833eb984682cdb5d7767440f31e0e9ef kali-linux-e17-2018.2-amd64.iso
63bd3eb798e0beebaabfe1b4415dcdd7e672237f kali-linux-kde-2018.2-amd64.iso
5aa34bda89529c529be81089d93d58c7dd2fb62f kali-linux-lxde-2018.2-amd64.iso
28a4e16695f72f2f128ef16ddd8ce68f76533ead kali-linux-mate-2018.2-amd64.iso
5594fc1f6de542c6b892063c7f8321a30c74d232 kali-linux-xfce-2018.2-amd64.iso
0bdd03a63dbbfccc8dd822ac2683371c5801ea8b kali-linux-light-2018.2-armhf.img.xz