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Comment by datameta | Hacker News Reader

This might be completely naive but can a reversible time component be incorporated into distinguishing two hash calculations? Meaning when unpacked/extrapolated it is a unique signifier but when decomposed it folds back into the standard calculation - is this feasible?

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Some hashes do have verification bits, that are used not just to verify intact hash, but one "identical" hash from another. However, they do tend to be slower hashes.

Do you have an example? That just sounds like a hash that is a few bits longer.

Mostly use of GCM (Galois/Counter Mode). Usually you tag the key, but you can also tag the value to check verification of collisions instead.

But as I said, slow.

hashes by definition are not reversible. you could store a timestamp together with a hash, and/or you could include a timestamp in the digested content, but the timestamp can’t be part of the hash.

> hashes by definition are not reversible.

Sure they are. You could generate every possible input, compute hash & compare with a given one.

Ok it might take infinite amount of compute (time/energy). But that's just a technicality, right?

Sure they are. You could generate every possible input

Depends entirely on what you mean by reversible. For every hash value, there are an infinite number of inputs that give that value. So while it is certainly possible to find some input that hashes to a given value, you cannot know which input I originally hashed to get that that value.

Oh, of course, the timestamp could instead be metadata!

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