You have probably seen them when downloading linux distributions or on official Vendor download sites. Hash’s. A Hash (informally called a checksum) is a signature for a file. This signature verifies integrity of said file. If you change the file in any manner, it’s checksum changes. Not many people use checksums for various reasons. You should use them when applicable. Let’s walk through checking a file downloaded from an official VMware site.
I will download VMware Horizon view 7.8. In the lower right corner of the download page is a list of checksums for the file. There are three different strengths. MD5, SHA1 and SHA256. There are several more but these are the most common. Getting into the details of each algorithm is beyond this article. You would get bored very quickly. Suffice to say you should use the highest algorithm provided. In this case it’s SHA256.
This is a closer look at the checksums.
Windows PowerShell 4.0 and higher contains a cmdlet that reads the checksum of a file. I downloaded the file Horizon 7.8 View Connection Server (64-bit) and ran this command against it.
The Get-Filehash command defaults to SHA256. The checksum is identical. This only took seconds to verify and now I’m sure there were no bits dropped during the download. I could also verify the file I have on hand from a local source is valid.
From the Website: 4eb12fc88c6cc95a85e93d03f62109549704f01b2d2cc64c76210bb30db28917
Output of the PowerShell command.
This method works on any file. If you created a very tightly controlled version of Windows Server 2016, run the Get-filehash command and record the checksum. When you want to use the ISO for an installation 2 weeks later, simply check the Hash. No matter if someone changed the name of another ISO to the same name and the file size is the same, the checksums will not match. Go forth and HASH.