Question

If I have both the initial key and the hash that was created, is there any way to determine what hashing algorithm was used?

For example:

• Key: higher
• Hash: df072c8afcf2385b8d34aab3362020d0
• Algorithm: ?

Answer 1

Well, given that there are a finite number of popular hash algorithms, maybe what you propose is not so ridiculous.

But suppose I asked you this:

If I have an input and an output, can
I determine the function?

Generally speaking, no, you cannot determine the inner-workings of any function simply from knowing one input and one output, without any additional information.

// very, very basic illustration
if (unknownFunction(2) == 4) {
    // what does unknownFunction do?
    // return x + 2?
    // or return x * 2?
    // or return Math.Pow(x, 2)?
    // or return Math.Pow(x, 3) - 4?
    // etc.
}