If you download a file from the web on a public WiFi and want to run on your machine you might want to check if the file has not been tampered with by a man-in-the-middle-attack or if the file host has been breached.
The easiest way to do this is to check the publised md5 or sha-1 hash for that file (you can do that via your phone if you want to be extra secure). Not every package publishes that but if they do it will be on their website usually next to the download link.
To verify the file you will need to hash the file you downloaded using openssl. For example:
$ openssl sha1 Kali-Linux-2016.1-vm-amd64.7z SHA1(Kali-Linux-2016.1-vm-amd64.7z)= 2b49bf1e77c11ecb5618249ca69a46f23a6f5d2d
Which matches the site’s published sha-1 hash:
If you want to check md5, simply replace
sha1 in the command with