The function of hashing tools

In your initial post, describe the function of hashing tools you can use to verify that two files are identical. For example, you can compare the hash value of a file on a website with the hash value of that file after you download it. If the hash values match, you downloaded the unmodified version of the website file.
Make sure to discuss the different elements that prove authenticity, and make sure to address how to determine whether the user attempting to access data is genuine or authentic.