A hash is a way of taking a bunch of data and returning a unique (or mostly-unique) signature. The nice thing is that if you change the data by just a little bit, the hash is then completely different.
The important feature is that it’s easy to compute the hash given the data but very difficult to recover the data given the hash, even though hashes are mostly unique. And the point, in this context:
You can use hashes to register advance predictions without revealing them. If you want to be able to publicly claim that a week ago you predicted that it would rain today, but without having revealed that fact until now, you can do it by publicly posting a hash of the text of such a prediction (e.g. “I, [your name], predicted on [last week’s date] that it will rain on [today’s date]”) a week ago, then today revealing the text. Anyone can now check that the text hashes to the hash you posted a week ago.
A hash is a way of taking a bunch of data and returning a unique (or mostly-unique) signature. The nice thing is that if you change the data by just a little bit, the hash is then completely different.
The important feature is that it’s easy to compute the hash given the data but very difficult to recover the data given the hash, even though hashes are mostly unique. And the point, in this context:
You can use hashes to register advance predictions without revealing them. If you want to be able to publicly claim that a week ago you predicted that it would rain today, but without having revealed that fact until now, you can do it by publicly posting a hash of the text of such a prediction (e.g. “I, [your name], predicted on [last week’s date] that it will rain on [today’s date]”) a week ago, then today revealing the text. Anyone can now check that the text hashes to the hash you posted a week ago.