In the quantum energy flux that comprises our existence, there is always another way round or through any locked door ;)

At a conceptual, high level, this is why trying to tie IP addresses, mac addresses, individual data packets, to a certified individual cannot ever be 100% reliable... just as it is impossible, as Sam says, to prevent any license protection system from eventually being cracked or circumvented.

Perhaps in a police state, a government sponsored corporation, or a corporately sponsored government, could exert the necessary control over every single internet access point, needed to make identification over the internet watertight?

But perhaps the irony there is that, in a police state, circumstantial evidence, propaganda and heresay, is usually good enough?

Whether you try and lock things down at a microcosmic, or a macrocosmic level, it seems there will always be a hole, a gap, a missing chunk... then you've got a leak, a flaw in your cosmic containment system, that you've so carefully modelled... and entropy kicks back in :)

Balancing on probabilities is perhaps the only reasonable / practical way to proceed...