Proof-of-Existence requires you to pay to get a timestamp verifiable back to the Bitcoin blockchain, because it's a highly inefficient one Bitcoin transaction-p

Proof-of-Existence requires you to pay to get a timestamp verifiable back to the Bitcoin blockchain, because it's a highly inefficient one Bitcoin transaction-per-timestamp system. The price is also quite a bit higher than the actual transaction cost - a fixed 5mBTC or $11 per timestamp. I'd suggest using the in-browser implementation of OpenTimestamps on https://opentimestamps.org https://opentimestamps.org if you want maximal ease of use. I personally use it all the time on my smartphone. OpenTimestamps uses a efficient system of merkle trees to aggregate timestamps, which allows us to timestamp an infinite number of documents with a single Bitcoin transaction. In the case of the Internet Archive effort, about half a billion documents with one transaction. Because this is so efficient, we're able to offer the service as a public good. The actual cost per timestamp is simply bandwidth, which even at the relatively high pricing of the VPS services myself and the other calendar operators are paying, works out to be about a millionth of a dollar per timestamp. I'm sure we'll be able to cover those operating costs indefinitely via donations. Frankly, my only concern is being able to get enough donations to pay myself a reasonable wage for my time, which so far I've had initial success in doing for the core protocol development (I'm doing the Internet Archive work explicitly pro-bono). You may find my detailed writeup on the architecture interesting: https://petertodd.org/2016/opentimestamps-announcement https://petertodd.org/2016/opentimestamps-announcement