How can I prove that I have added a folder to IPFS no later than a certain date?

Question

I would like to be able to prove that a certain set of files was available through IPFS at a certain date.

How can I achieve that without resorting to centralized solutions or third party authorities?

Thanks!

Answer 1

You could use a solution like opentimestamps to create a timestamp of your document using the Bitcoin network.

Answer 2

You can create an Ethereum smart contract which takes in an IPFS hash and ties it with the current block timestamp.

Anyone will then be able to look up an IPFS hash and see if it's in the smart contract and the timestamp, as well the public address who submitted the transaction.

If you don't want to use Ethereum you can use any reliable blockchain such as Bitcoin.