But when I proposed a scheme in my comments above (see here and here and here), the objections here were not really mathematical, but rather focused on the human factor, namely the possibility that the secret key would get leaked even if it was kept offline and only a few officials could have access to it (see this reply), along with one point about a technical limitation in possible key lengths built into some existing devices and software (which could be dealt with by making some legislation about allowing for longer key lengths in future releases). This suggests that claiming the idea is “mathematically impossible” is not really true at all, and that the main objections are in the fuzzier realm of predicting human behavior.
