TIL - how to make a public claim ahead of time

To make a claim now that you only want to reveal later, you can shasum the message.

Then keep the original message somewhere private, and post the sha to a public network.

Later, you can post the original message to prove the sha matches.

Example

# This is a message plus a nonce (+12h87s) - change the nonce.
# The nonce just adds complexity to reversing the hash.
echo -n "<Thing X> will happen on <date> +12h87s" | shasum -a 256
# a594484322572f90160bddbf8e98c33ed7ab5665159389838f6f52454b88c30b

So you post a594484322572f90160bddbf8e98c33ed7ab5665159389838f6f52454b88c30b to your Twitter page. No one can use that alone to reverse what you said, but by putting it on your profile you’ve publicly timestamped when you said the thing.

Later, when you are free to publicly disclose the original message, just post the thing you used to generate the sha, which is very strong proof you originally wrote it.

echo -n "<Thing X> will happen on <date> +12h87s" | shasum -a 256