[baotrungtn]

You need gas to post your "Release" to Ethereum blockchain and gas costs money. How is it possible to be free?

[flixic]

It costs about 0.8 ETH per year to run, and I’ve personally funded it with 1 ETH. I do appreciate donations: https://cryptoproof.org/support

[crazydoggers]

I’m guessing they are subsidizing it. On the how it works page it says

“Any message, regardless of its original size, only generates a 32 byte content hash and costs about $0.03 to submit to the blockchain.”

Also

“CrypoProof is free to use because instead of sending each content hash as a separate transaction, CryptoProof combines all the hashes posted during the same hour into a Release. The release simply contains all the content hashes posted that hour.”