User gets URL via webmail on Chrome, Chrome pre-fetches the URL. User closes Chrome because Starbucks is closing. When she finally visits the URL for the "first time" it's nuked.
Etc. etc.
Unexpected behavior is unexpected.
Therefore, the secret shouldn't be obtained from a GET, but rather a POST. A button or jQuery.post on the 'shared' page, for example, that fetches and causes the deletion.
I like this idea though.
We're considering changing the basic UX to require a click to display the secret (the click will send a POST to retreive the contents). That will include a much more visible disclaimer that it's only available one time.
• loading starts a countdown timer, visible on screen: after that long, the message is destroyed. (In the meantime, an iPad re-download succeeds.)
• the reader sees a big button on the page which must be pressed to complete deletion (or to speed deletion, if the above timer is counting down).
* on initial load, the browser is given a unique cookie (or even decryption key); from then on, even if the message has an additional countdown 'grace period' (of seconds, days, or longer), only that one browser can reload (or decrypt) it.
(That 'problem' wasn't even mentioned in the parent to which I was responding.)
Unexpected behavior doesn't happen every time.
As an optimization, if you have a self hosted service of this sort that gives proper logs, you can probably verify that the link wasn't intercepted by looking at the source IP and comparing to what the user reports (if they're able to do that, if not, you fall back to assuming it was compromised), and if so, skip the revocation/regeneration procedure.
I don't know if it prefetches links in webmail, however, and that would be about the only situation I can think of where this might happen.
Edit: of course, now that I posted this, I can't seem to make it work. I promise it does happen.
Your demo link seems broken, it prefetches a new page every time you mouseover, not just once. Also, there's autoplaying audio ads, something that I can only regard as a bug.
I'm sure there are other issues. GETs are kind of unreliable. Better to do this stuff via POST.