Can’t the steps be reversed one by one to get back the original?
In: Mathematics
SHA is a hashing function. It has multiple inverse. But your question still hold, why can’t we easily find one inverse?
And it’s hard because it’s like a puzzle that you build from the solution. For example: take a password, give a unique number to each symbol, then you compute the sum of all those numbers and the product of all those numbers. Your hash is this sum and product.
Now inversing this means you need to find a list of numbers of which the sum and products are a match. It’s suddenly harder. There are many solutions, but they are tricky to find, you need to solve the puzzle, while building the puzzle from the solution was easy. And if somebody give you a valid solution, it’s easy to check it’s valid.
SHA256 has 256 puzzles to solve all at the same time (sum and product is only 2), and they are carefully chosen so that it’s hard to correlate each of them to each others.
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