It could bring you into more problems than you started with.
https://en.wikipedia.org/wiki/Trusted_timestamping
EDIT: There's also newer ones that pull the site for you like a MITM to do what we're saying. Startups come and go, though, so I recommend scripted or manual scraping combined with long-running notary who will have evidence when trial happens. :)
I'm thinking in purely technical terms here, and that I can easily argue that such evidence is inadmissible, unless there's a certain number of independent, trusted snapshot services that would archive each link too, and allow one to compare the decrypted archive. To achieve that, one would probably want to use an indirection for linking so that such archives do not have to archive everything that exists, but just those that go through said indirection.
Then, the last question is how many independents you need to put trust in the verification, considering that motivated attackers could circumvent, say, the 3 most used archiving services. Or you could bind the archival of a link in a federated number snapshot services to a consensus algorithm. Then you'd ask yourself how many networks (which consist of multiple services) you'd trust.
2. The notary could make their archive public, so that any interested party could go through and verify that it is legit.
3. By using many different notaries the chance of any one of them being bad would be reduced.
http://www.surety.com/digital-copyright-protection/prove-own...
You publish the hash chains with signature in places you can't retract. They use New York Times for instance. Far as their sigs, they can use one or more HSM's. One or more atomic clocks plus high-quality NTP for timing. Open-source client checks all of it right after it happens, maybe keeping local copy. Every other aspect is just standard INFOSEC.
I dont have time to answer the last question right now. Off to work. :(
It's not what was at the sender though, surely, it's what gets sent to the client. Each client receives different content (at some level).
If I paste a 'forbidden' link to my blog that I've never followed, and no-one ever views the page, surely that's not a crime??
Exactly, and now imagine how easy it is for someone motivated and with the right resources to meddle with that.
Similarly, it's hard to prove a machine was used by its user to consciously navigate to an illegal link. There's too much automatism on the web and on networked machines, plus if we consider link shorteners, there are too many explanations against that would not allow admitting evidence like machine-x-owned-by-mike-miller-accessed-mp3forfree-artist-album-2016.pdf.
It's the equivalent of me walking in a street where I didn't know drugs or weapons or humans were sold, and being arrested for just walking through there. In real life you have some clues where not to go, especially if you're from the town, but on the internet it's too easy to have your machine load a random illegal link or search alarming terms on Google without your consent.
Next you'll be wanting trials instead of summary rulings.