Hash functions explained in a simple way

Understanding how hash functions work

First, what is a hash function?

Simply speaking, a hash function is a mathematical function that takes any input size and convert it to a fixed output size. Consider this simple hash function H(X) = Last digit of (X)

• H(1234) = 4.
• H(12567) = 7.
• H(127) = 7.
• H(1111111111) = 1.
• H(24)=4.
• H(24)=4.

So no matter what is the input and its size, we’re returning a one digit output. Another important property is that the same input will always give you the same output. H(24) will always be 4.

In summary:

• A hash function generates a fixed size output (called digest or hash)
• For any input size or length, we get always the same fixed output size
• Totally deterministic: for the same input we get always the same output
• It’s not a complicated operation to get the hash of any input (very easy)
• Several inputs can have the same hash (like here 127 and 12567 both have 7 as hash). That’s called a hash collision. It’s natural since the output has a fixed size, and…