You can do this already by yourself or use a service which you need not even trust. Every x seconds, collect all the pieces of data that need to be notarized a

You can do this already by yourself or use a service which you need not even trust. Every x seconds, collect all the pieces of data that need to be notarized as existing in the world prior to some time t. It can be an arbitrary amount of data. Construct a Merkle Tree[1] of all the hashes (or HMACs) of all the data to be notarized. Compute the Merkle Root. Make sure that everyone gets their Merkle Proof (path from leaf to root) or publish the Merkle Tree publicly. Embed the Merkle Root into a one or more cryptocurrency blockchains to exploit their immutability guarantees. By either including it as "additional data" to some transaction or just straight up as a fictional cryptocurrency address. Every piece of data processed in this way will have a Merkle Proof (cryptographic path from hash of the data to the Merkle Root) that proves it existed prior to the creation of the Merkle Root. The Merkle Root will have its creation time bounded by the proof of work conducted on the cryptocurrency blockchain. [1] <https://en.wikipedia.org/wiki/Merkle_tree https://en.wikipedia.org/wiki/Merkle_tree>