Giulio via Sigsum-general sigsum-general@lists.sigsum.org writes:
Summarizing: is there a way to use the Sigsum log server and the witnesses to attest that an inclusion happened at a specific timestamp?
The witness timestamps say that everything up to the witnessed tree size was included at that time. One could alwaye get fresh timestamps on a newer treehead. As you say, if one is willing to make assumptions on how tree size grows with time, you could turn the (tree size - leaf index) difference into an estimated submission time, but that does sound a bit brittle.
What you can do is to also get a cosigned treehead *prior* to submit, then you know that any items with higher leaf index was *not* included at that time. Should give you sufficient granularity to prove, e.g., that an item was submitted during office hours.
If that is useful for your case, I don't know. You only get a bound for the submission time for this log; the data could have existed, and maybe logged elsewhere, much earlier. And we also make rather weak promises regarding duplicate log entries.
Regards, /Niels