A hash function is a mathematical algorithm that takes an input of any size and produces an output of a fixed size. It is used to create digital signatures, store passwords, and check data integrity.
For example, when a user signs up for an online account, the website may use a hash function to securely store the user’s password. The website will take the user’s password, run it through the hash function, and store the output of the hash function instead of the user’s actual password. When the user tries to log in, the website will run the user’s input through the same hash function and compare the output of the hash function to what is stored in the database. If they match, then the user is authenticated.