Can’t the steps be reversed one by one to get back the original?
In: Mathematics
There is one very obvious way to answer your question.
You can take the sha256 of any size of data. That means you can take the sha256 of a huge video file that’s many gigabytes. The result is a hash that is only a few hundred bits.
It should be obvious that you can’t take a few hundred bits of data and somehow “reverse” it into a file that’s many gigabytes in size. This is because any general-purpose hash algorithm that takes arbitrary input *must* lose information along the way.
Many mathematical operations lose information. For example, the remainder function (called “modulus” by us nerds). If I asked you, “I divided a number by 7 and the remainder is 3, what was the original number?” Could you answer? You might get lucky, but there are infinite possible numbers I might have used. Even knowing the answer and knowing exactly what mathematical operation I performed, you can’t reverse it and get the original number.
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