[codetrotter]

Make a PDF or whatever kind of document containing the things you want to reveal.

Make a hash sum of the file.

Publish the hash of the document somewhere. Like on your Mastodon timeline or on Reddit, or on HN, or as an ad in a national printed newspaper.

Make sure the text is pretty long though. If you write something super short someone could guess the hash for it.

Write a short comment along with the hash. Something like:

“My prediction will be revealed on Dec 31 2025. Sha256 a9774a1a6ebf564cc408cfd86b5f2c06c13d830e143989714d958d34f325db13.”

When time comes, publish the document.

[codetrotter]

Another alternative is to encrypt the document with a very strong pass key, and publish only the encrypted document now along with an announcement that the key to decrypt it will be published on such and such date.

If you are on a platform that doesn’t support posting attachments you can use IPFS or similar to host the encrypted file.

[gus_massa]

Bonus points if it's a platform where you can't delete the posts. Or you number the posts like

> My prediction 683 will be revealed on Dec 31 2025. Sha256 a9774a1a6ebf564cc408cfd86b5f2c06c13d830e143989714d958d34f325db13.

> My prediction 684 will be revealed on Nov 7 2025. Sha256 17147091grhef7wy89908409849rwiruriwu87w980241989171n109288021982.

It would even be better to add it to a blockchain to ensure there is no backdating.

[pvg]

If you write something super short someone could guess the hash for it.

You can skip the pdf and unless the thing is so short/predictable you can guess it outright, nobody is going to 'guess' the hash. E.g. 'I made up a random 64 byte sequence, here's its cryptographic hash, guess the sequence' - that doesn't happen.

[codetrotter]

If the sentence is too short it might be possible to guess.

It’s not going to consist of random bytes.

Imagine for example that a high profile celebrity accused of murder has successfully defended himself in court and on that day he tweets:

I have something to reveal, but I won’t be telling you until the year 2135. Sha256 73fa194342af6b6e355e129fafd9b19d2a63589b1e3c6e2b5d94a7ca1b3e25f6

If this happens to be a short sentence related to recent events, don’t you think someone will figure out what he wrote pretty soon?

[pvg]

You can just pad or HMAC the short sentence.

[codetrotter]

Absolutely. Padding it falls under making sure the text is not too short.