An (interesting, but impractical) solution to this problem would be to use astronomy to deduce the current date first, which should be good enough to validate t

An (interesting, but impractical) solution to this problem would be to use astronomy to deduce the current date first, which should be good enough to validate the certificate. See this QA on Astronomy StackExchange: https://astronomy.stackexchange.com/questions/12886/get-date-and-time-by-position-of-the-sun-and-the-observer-position https://astronomy.stackexchange.com/questions/12886/get-date...