[j_s]

I would be interested in an attestation service that can provide court-admissable evidence that a particular piece of content was publically accessible on the web at a particular point in time via a particular url.

I believe the only way to incentivise participation in such a system is by paying for timestamp'ed signatures, eg. "some subset of downloaded [content] from [url] at [time] hashed to [hash]" all tucked into a Bitcoin transaction or something. There are services that will do this with user-provided content[1]; I am looking for something that will pull a url and timestamp the content.

This would also be a way to detect when different users are being served different content at the same url, thus the need for a global network of validators.

[1] https://proofofexistence.com/

[rjeli]

Interesting - it is trivial to prove something was done today rather than yesterday, by hashing with the most recent bitcoin block or some new info.

Is it possible to prove something was done in the past? All I can think of is some sort of scheme involving destroyed information.

[j_s]

trivial to prove something was done today

My focus is on the something much more so than the when. I can do my own doctoring of any data, or use some service to make something that looks real[1]. Getting some proof that this fake data existed is not what I'm after.

Instead, I want multiple, completely separate (and ideally as independent and diverse as possible) attestations that something was out there online, as proof that some person or organization intended for it to be seen by everyone as their content. Being able to prove that irrefutably seems nearly impossible today even for the present time, particularly against insider threats.

Your question regarding proving something in the past is going far beyond what I'm hoping for; it will take me quite a while to come up with anything that might be helpful for such a situation. I assume most would hit up the various archive sites, but my gut feeling is that it winds up being a probability based on how well forensics holds up / are not falsifiable.

[1] simitator.com - not linking because ads felt a bit extra-sketch!

[naiveattack]

This is interesting.

The only way to do it should be to sync your observation to other observers as soon as the observation is made. The other observers can confirm the time then by knowing when they received the information.

Block chain with comments.

[an27]

Isn't it the other way around?

I can prove I had today's papers today, but once I've seen it I can prove it any day. So you can say "this information existed at day X or earlier".

There's also the issue of proving the content you hashed actually came from the place you say it came from. To me it seems that would require proofs of authenticity, by the source itself; not something that's easy to come by.